JP7576966B2 - Reinforced platinum alloy, method for producing the reinforced platinum alloy, and glass production apparatus - Google Patents

Description

The present invention relates to a strengthened platinum alloy suitable as a component material for manufacturing equipment for various glass materials. In particular, the present invention relates to a strengthened platinum alloy of a particle dispersion type in which Zr is an essential additive element and oxide particles of the additive element are finely dispersed.

Oxide particle-dispersed reinforced platinum alloys have been used as a component material for manufacturing equipment for various glass materials such as optical glass and glass fiber. In the manufacture of glass materials, molten glass melted at a high temperature of 1000°C or higher is refined and stirred, and then molded and spun. In towers and tanks (melting tanks, etc.), stirring media (stirrs), spinning bushings, etc. that handle such high-temperature materials, good high-temperature strength and high-temperature creep resistance are required to avoid damage such as deformation and cracking at high temperatures. Reinforced platinum alloys are alloy materials in which oxides of additive elements such as Zr, Y, and Ce are finely dispersed in a matrix made of platinum or platinum alloys (PtRh alloys, etc.). Platinum and its alloys, which are the matrix, are high-melting point metals and also have excellent chemical stability. Reinforced platinum alloys, which have increased strength due to particle dispersion strengthening with oxide particles, have higher high-temperature strength and high-temperature creep resistance than platinum, etc. This reduces deformation and damage during operation of the glass manufacturing equipment, and also reduces the risk of contaminating the molten glass.

A known method for producing a strengthened platinum alloy is the powder metallurgy method, which uses a platinum alloy powder in which oxide particles are dispersed, as a precursor, which has been oxidized and cast. In the powder metallurgy method, a platinum alloy consisting of platinum and additive elements is first produced by melt casting, which is then atomized to produce a platinum alloy powder (atomized powder). The platinum alloy powder is then oxidized to turn the additive elements into oxide particles, and the platinum alloy powder is compressed and molded, and then appropriately forged or rolled to produce a strengthened platinum alloy. The applicant of the present application has conducted extensive research into strengthened platinum alloys, both in terms of the material composition, such as the type and composition range of additive elements, and the manufacturing process (Patent Documents 1 to 6). Based on the knowledge gained from these research, the applicant has also succeeded in commercializing an effective strengthened platinum alloy for glass manufacturing equipment (for example, the nanoplat (registered trademark) series is an example of a strengthened platinum alloy product by the applicant of the present application).

Japanese Patent Application Publication No. 06-336631 Japanese Patent Application Publication No. 08-134511 JP 2000-160268 A JP 2006-057164 A International Publication No. WO2002/083961

In all of the above-mentioned conventional technologies, the aim is to increase the high-temperature strength of the strengthened platinum alloy and improve its high-temperature creep resistance, while adjusting the material composition and improving the manufacturing process. The conventional strengthened platinum alloys completed in this way are applied to the various glass manufacturing devices mentioned above.

The glass manufacturing equipment described above, which uses conventional reinforced platinum alloys, operates stably in most cases without deformation, cracks, or other damage. However, it has been confirmed that cracks occur at unexpected times in some glass manufacturing equipment. It has also been confirmed that this particular problem tends to occur at the bottom of the molten glass melting tank. When cracks occur in the melting tank, it is possible to continue using the equipment by repairing it, but this is only temporary and requires the equipment to be replaced, which raises concerns about its shortened lifespan.

The cause of the cracking of the reinforced platinum alloys seen in some of these glass manufacturing equipment is not necessarily clear. This is because there is no clear difference in the composition of the materials in which the cracks occurred compared to the materials used in other glass manufacturing equipment in which cracks do not occur. In terms of operating conditions, there is also no significant difference in the operating temperature or atmosphere of the various components of the glass manufacturing equipment. Furthermore, the dimensions of each component, such as the shape and thickness, are designed to suit each application, so it is difficult to imagine that the operating conditions are a factor.

The present invention was made against the background described above, and aims to clarify the causes of damage such as cracks that can occur when oxide dispersion strengthened platinum alloys are applied to glass manufacturing equipment, and to provide a method for effectively avoiding such damage. It also aims to provide a glass manufacturing equipment that uses this strengthened platinum alloy.

In order to solve the above problem, the inventors first studied the causes of breakage observed in some glass manufacturing equipment. As a result, they concluded that conventional reinforced platinum alloys are prone to cracking due to their excessive strength depending on the glass manufacturing equipment to which they are applied. According to the inventors, it has been confirmed that the cracking problem of reinforced platinum alloys occurs mainly at the bottom of the melting tank, especially at the bottom outer periphery. Melting tanks made of reinforced platinum alloys are often manufactured by drawing a plate material. The bottom outer periphery of the melting tank has an R-shaped cross section, and this part is particularly highly processed. Due to the dispersion effect of oxides, reinforced platinum alloys have higher strength than melting materials without dispersed particles. However, because of their high strength, they have high processing resistance, and it can be said that they are in a state where lattice defects such as distortion and dislocations are easily accumulated due to the increase in the degree of processing. Therefore, it can be said that the bottom outer periphery of the melting tank tends to be a starting point for cracks.

The cracks occur and grow due to the load caused by the temperature change during the operation of the glass manufacturing plant. The melting tank of the glass manufacturing plant is a device for melting glass raw materials to produce molten glass and sending it to the next process, and raw materials may be added to the molten glass during melting. When raw materials are added, the temperature of the molten glass drops. In addition, the type of glass produced in the glass manufacturing plant is not always the same and is changed according to demand. Therefore, the type of glass melted in the melting tank changes, and such a change in the type of glass also causes a temperature change. Furthermore, the cycle of operation and stop of the equipment also causes a temperature change. The temperature change in the glass manufacturing equipment due to the above various factors causes thermal stress. The occurrence of such thermal stress is not limited to the melting tank. However, as described above, the bottom outer periphery of the melting tank, which includes the starting point of the crack, is easily affected by thermal stress and is thought to be prone to cracks.

As described above, the inventors have concluded that the cause of cracks occurring in glass manufacturing equipment (melting tanks) is the excessively high strength of the strengthened platinum alloy, which is the material from which they are made. In this regard, it can be said that the main focus in the development of strengthened platinum alloys in the past has tended to be on improving high-temperature creep properties. However, based on the above considerations, it is difficult to say that simply increasing high-temperature strength is effective. It is believed that, as a means of preventing cracks, priority should be given to imparting flexibility, and excessive high-temperature strength and high-temperature creep resistance should be suppressed.

One method of suppressing the high-temperature strength and high-temperature creep resistance of a strengthened platinum alloy is to reduce the content of added elements and the amount of dispersed particles. However, even if suppressing high-temperature strength and high-temperature creep resistance is necessary to impart flexibility, it is difficult to say that it is desirable to reduce them excessively. In particular, in platinum alloys with too low high-temperature creep resistance, the deformation mode at high temperatures becomes a simple high-temperature deformation, and there is a risk that the load alone will cause deformation or damage to the device. In the example of the molten glass melting tank mentioned above, this could cause deformation in parts other than the bottom.

Therefore, the inventors of the present invention have started by reconsidering the manufacturing process in order to develop a strengthened platinum alloy that has flexibility that is less susceptible to the accumulation of distortion due to the above-mentioned processing while ensuring sufficient high-temperature creep resistance by minimizing the content of additive elements. As a result of extensive investigation, they have found that the above-mentioned problems can be solved by limiting the upper limit of the content of additive elements and by providing a strengthened platinum alloy that has the specified properties at high temperatures and room temperature, and have come up with the present invention.

The present invention, which solves the above problems, is a strengthened platinum alloy in which dispersed particles of oxides of additive elements are dispersed in a matrix of Pt or PtRh alloy, the strengthened platinum alloy essentially containing 0.04% by mass or more and 0.25% by mass or less of Zr as the additive element, with the remainder consisting of the constituent metals of the matrix, oxygen, and unavoidable impurities, and characterized in that the creep rupture time in a high-temperature creep test at 1400°C and a stress of 10 MPa is 100 hours or more, and the rupture elongation in a room-temperature tensile test is 35% or more.

As described above, the strengthened platinum alloy of the present invention has relatively high high-temperature strength (high-temperature creep resistance) while limiting the content of Zr, which is an essential additive element, to 0.25 mass%. On the other hand, the strengthened platinum alloy of the present invention is a platinum material with large tensile elongation (breaking strain) at room temperature and flexibility. The structure and characteristics of the strengthened platinum alloy of the present invention are described below.

(I) Structure of the strengthened platinum alloy according to the present invention (I-1) Constituent elements and composition of the strengthened platinum alloy according to the present invention The constituent elements of the strengthened platinum alloy according to the present invention are additional elements with Zr being an essential additional element, Pt or Pt and Rh which are constituent elements of the matrix, oxygen, and unavoidable impurities.
(1) Additive elements The additive elements exist in the form of oxides in the strengthened platinum alloy and contribute to strengthening the alloy as dispersed particles. Zr is an essential additive element because Zr oxide (ZrO ₂ ) has a thermal expansion coefficient relatively close to that of Pt. In addition, Zr oxide is less likely to have adverse effects such as coloring on molten glass. Furthermore, Zr has a lower oxide formation free energy than Pt, so it is easy to form dispersed particles. As described later, in the present invention, it is required to highly oxidize the additive elements contained in trace amounts in the alloy to form ultrafine oxides. In order to meet the above characteristics and requirements, Zr is an essential additive element.

Zr is an element for strengthening platinum alloys, but it is also a useful additive element from the viewpoint of ensuring tensile elongation (breaking strain) at room temperature, which is related to flexibility. In the present invention, both high-temperature creep properties and room-temperature tensile elongation are set to a certain level or higher, and Zr is an essential additive element for obtaining a platinum alloy with such an excellent balance. In this respect, Y and other additive elements, which have traditionally been known as additive elements for strengthening platinum, do not have the same effect as Zr. Even if only Y or other elements are added instead of Zr, improvements in high-temperature creep properties are observed, but the effect of improving room-temperature tensile elongation is poor. As described below, in the present invention, the addition of Y and other elements is permitted only as an auxiliary addition together with Zr.

The content of Zr, which is an essential additive element, is 0.04 mass% or more and 0.25 mass% or less based on the mass of the entire strengthened platinum alloy. If the content of the additive element is less than 0.04 mass%, the strengthening effect of the additive element and its oxide is poor, and high-temperature strength is low. Considering the objective of the present invention, which is to ensure sufficient high-temperature strength, the Zr content must be 0.04 mass% or more.

Although the high-temperature strength of the strengthened platinum alloy increases with an increase in the Zr content, the addition of a certain amount of Zr reduces the high-temperature strength. In addition, as the content of Zr and other additive elements described below increases, there is concern that the weldability may deteriorate. Deterioration of weldability refers to the generation of slag (slag) due to oxides in the weld metal (bead) during welding, the decrease in stability of the molten metal due to oxides, and the generation of oxide aggregation. As described above, since the objective of the present invention is to ensure sufficient high-temperature strength, it can be said that there is no need to add Zr until a tendency for high-temperature strength to decrease or weldability to deteriorate occurs. Therefore, in the present invention, the upper limit of the Zr content is set to 0.25 mass%.

The Zr content in the present invention is within the above range, but the strengthened platinum alloy of the present invention is further characterized by the Zr content within this range. This will be described in detail in the explanation of creep strain rate below.

In addition, in the present invention, at least one of Y, Ce, Sc, and Hf can be added as an additional element other than Zr. This is because, based on the applicant's previous findings, oxide particles of these elements can also act as a strengthening factor for strengthened platinum alloys and improve high-temperature creep properties. The amount of these other additional elements added, in total with Zr, is 0.04 mass% or more and 0.25 mass% or less. However, the addition of these other additional elements is not essential. In the present invention, the strengthened platinum alloy may be one to which only Zr is added as an additional element.

(2) Matrix constituent elements (Pt, Rh)
The strengthened platinum alloy according to the present invention is a dispersion strengthened alloy with a matrix of Pt or a PtRh alloy. Therefore, Pt or Pt and Rh are the main constituent elements in the present invention. The PtRh alloy is used as the matrix in addition to Pt in order to improve the strength of the matrix. When the matrix is a PtRh alloy, the content of Rh is preferably 5% by mass or more and 40% by mass or less, more preferably 5% by mass or more and 20% by mass or less.

(3) Oxygen Oxygen exists in the form of oxide together with the additive elements such as Zr in the strengthened platinum alloy. Therefore, oxygen can be said to be an essential element. The oxygen content of the strengthened platinum alloy varies depending on the content of the additive elements, the conditions of the oxidation treatment in the alloy manufacturing process, the content of inevitable impurities in the platinum alloy before the oxidation treatment, etc. The oxygen content of the strengthened platinum alloy according to the present invention is preferably 1.0 to 2.0 times the theoretical oxygen content caused by the oxides of the additive elements such as Zr. The theoretical oxygen content is the oxygen atomic concentration in the alloy when it is assumed that all the additive elements in the strengthened platinum alloy have produced oxides. The theoretical oxygen content is calculated based on the content of each additive element, assuming that the oxide of each additive element is an oxide of stoichiometric composition (ZrO ₂ , Y ₂ O ₃ , CeO ₂ , etc.).

In the present invention, the content of the additive elements is limited to ensure the necessary and sufficient high-temperature strength and to prevent the strength of the strengthened platinum alloy from becoming excessively high. However, it is also undesirable for the strength to become too low. For this reason, it is necessary to ensure the appropriate strength by making the limited amount of additive elements as oxides as much as possible. In the present invention, if the oxygen content of the strengthened platinum alloy is less than 1.0 times the theoretical oxygen content, there is a high probability that unoxidized additive elements are present. On the other hand, based on the above definition of the theoretical oxygen content, there is a limit to the amount of oxygen that the strengthened platinum alloy can contain. In addition, the presence of oxygen due to the oxidation of unavoidable impurities should also be taken into consideration. For this reason, the upper limit of the ratio to the theoretical oxygen content is set to 2.0 times.

Due to the influence of inevitable impurities, the difference (deviation) between the oxygen content of the strengthened platinum alloy and the theoretical oxygen content tends to increase as the content of added elements such as Zr decreases. This is because, if the raw materials and manufacturing method are the same, it should be considered that the type and content of the inevitable impurities are not affected by the amount of the added elements. For example, suppose there is a strengthened platinum alloy with a Zr content of 0.04 mass% (400 ppm) and 400 ppm of inevitable impurities. If it is assumed that all of the Zr and inevitable impurities in this strengthened platinum alloy are oxidized, the oxygen content can be 2.0 times the theoretical oxygen content. When a strengthened platinum alloy with a Zr content of 0.08 mass% (800 ppm) is manufactured using the same raw materials and manufacturing process as this strengthened platinum alloy, the content of inevitable impurities will be the same, and if it is assumed that all of the Zr and inevitable impurities are oxidized as described above, the oxygen content can be 1.5 times the theoretical oxygen content. As shown in this example, the total oxygen content of a strengthened platinum alloy is affected by inevitable impurities when the amount of added elements is low. However, the ratio to the theoretical oxygen content shown in the above example is merely an example. In reality, the ratio to the theoretical oxygen content can show various values within the range of 1.0 to 2.0 times, depending on the type of inevitable impurities and the presence or absence and type of added elements other than Zr.

The oxygen and nitrogen analysis method is currently known as a relatively accurate analytical method for the oxygen content of strengthened platinum alloys, and can be applied to the present invention. Note that the oxygen content of the strengthened platinum alloy of the present invention has some effect on the strength of the alloy, but the oxygen content alone does not explain the characteristics of the present invention. This point will be described in detail later.

(4) Inevitable impurities Examples of the inevitable impurities in the strengthened platinum alloy according to the present invention include Al, Fe, Co, Ni, Si, W, etc. In addition, precious metals such as Pd, Au, Ag, Ir, and Ru can also be inevitable impurities. Furthermore, when the matrix is Pt (pure Pt), Rh can also be an inevitable impurity in addition to the above. These inevitable impurities originate from the impurities contained in each raw material metal (Pt, Rh) when manufacturing the master alloy, and may also be mixed in from processing equipment such as compression molding and forging. However, as described later, the strengthened platinum alloy according to the present invention can be manufactured by a relatively simple process that does not require wet grinding or degassing of platinum alloy powder, so that the inclusion of impurities during the manufacturing process is reduced. It is preferable that the content of these inevitable impurities unintentionally contained is 500 ppm or less in total.

(I-2) Material structure of the strengthened platinum alloy according to the present invention The strengthened platinum alloy has a material structure in which oxide particles are dispersed in a matrix (parent phase) of platinum or a platinum alloy. The strengthened platinum alloy according to the present invention is similar, and oxide particles of an additional element, Zr being an essential element, are dispersed in a matrix of a Pt or PtRh alloy.

In the present invention, the average particle size of oxide particles that can be measured by a normal observation method is preferably 1 μm or less. Dispersion strengthening by oxide particles works by highly dispersing fine particles. In addition, the lower limit of the average particle size of oxide particles is preferably 0.01 μm or more if oxide particles that can be measured by a normal observation method are the target. The normal observation method is an observation method using an electron microscope such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The particle size can be measured by a biaxial average or a circle equivalent diameter. Since the oxide particles in the strengthened platinum alloy often have a shape close to a sphere, there is no need to limit the method of measuring the particle size.

However, according to the inventors' estimation, the strengthened platinum alloy according to the present invention is believed to have oxide particles that are difficult to detect by the above-mentioned normal observation method. In the present invention, the content of the additive element is set to a very small amount, and it is believed that the additive element in the mother alloy before oxidation is in a solid solution in a fine state at the atomic level. Such additive elements can also generate oxide particles by appropriate oxidation treatment, but it is difficult to clearly observe them, and it is difficult to measure their particle size. It is unclear to what extent such ultrafine oxide particles exist compared to oxide particles that can be observed by normal methods. However, the inventors consider that these ultrafine oxide particles act to improve the material structure of the strengthened platinum alloy and to obtain the flexibility of the material in the room temperature range. The reason why the strengthened platinum alloy has excellent high-temperature strength is not only the dispersion strengthening by the oxide particles, but also the material structure of the matrix. The matrix of the strengthened platinum alloy exhibits a material structure in which leaf-shaped crystal grains with a large aspect ratio are alternately stacked. In the present invention, it is estimated that the above-mentioned ultrafine oxide particles efficiently improve the matrix to such a suitable material structure. It is believed that the effect of these ultrafine oxide particles is exerted simultaneously with the effect of normal oxide particles (dispersion strengthening), or is exerted separately. And because these ultrafine oxide particles are difficult to observe, their composition cannot be identified.

(II) Physical Properties of the Strengthened Platinum Alloy of the Present Invention As described above, the strengthened platinum alloy of the present invention is specified by specifying both the creep properties (creep rupture time) in a high-temperature creep test and the tensile properties (rupture elongation) in a room-temperature tensile test.

(II-1) High-Temperature Creep Properties The strengthened platinum alloy according to the present invention is required to have a creep rupture time of 100 hours or more in a high-temperature creep test at 1400°C and a stress of 10 MPa. The strengthened platinum alloy according to the present invention is an invention made from the discovery that excessively high high-temperature strength was a cause of problems in conventional strengthened platinum alloys. However, it is not preferable to reduce the high-temperature strength excessively. In the present invention, the creep rupture time in the creep test described above is specified as the necessary and optimal high-temperature strength. The creep test conditions of a temperature of 1400°C and a stress of 10 MPa are set in order to impose a load larger than the operating temperature and applied stress of a melting bath, etc.

The high-temperature creep properties of the strengthened platinum alloy according to the present invention described above do not clearly exceed those of conventional strengthened platinum alloys, but are almost comparable to them, with the difference being slight. Since one of the objectives of the present invention is to ensure sufficient high-temperature strength, it is not necessary for the alloy to exhibit high-temperature creep properties that are clearly superior to those of conventional techniques.

Regarding the measurement and evaluation of the above creep properties, a general high-temperature creep test can be applied. For example, the test method specified in the Japanese Industrial Standard JIS Z 2271 "Method of creep and creep rupture test for metallic materials" can be applied for the high-temperature creep test. The rupture time at a specified stress can be measured from the creep curve (stress-rupture time) obtained by the high-temperature creep test. The rupture time at the above-mentioned stress of 10 MPa can also be obtained based on the created creep curve. Note that when specifying the rupture time at a stress of 10 MPa, the actual measured value at that stress may be applied, but the rupture time at that stress may also be obtained by extrapolating or interpolating based on the above-mentioned creep curve.

(II-2) Room temperature tensile properties In addition to the high temperature creep properties, the strengthened platinum alloy according to the present invention is required to have a breaking elongation of 35% or more in a room temperature tensile test. This breaking elongation property is a property that suggests the flexibility and softness of the material at room temperature. The strengthened platinum alloy according to the present invention can suppress the accumulation of strain and lattice defects introduced by processing by acquiring flexibility at room temperature. Glass manufacturing equipment such as melting tanks are usually manufactured by processing at room temperature. As described above, melting tanks are often manufactured by drawing, and the degree of processing of the bottom outer periphery is high. According to the present invention, it is possible to manufacture melting tanks and the like with less accumulation of damage due to processing, and cracking and breakage during their operation can be suppressed.

In the above conventional strengthened platinum alloys with dispersed oxide particles, it is difficult to achieve a breaking elongation of 35% or more in a room temperature tensile test while increasing the high temperature strength. This breaking elongation is equal to or greater than that of a molten Pt (pure Pt) material without dispersed particles. In the present invention, the breaking elongation in a room temperature tensile test is more preferably 40% or more. However flexible it is, there is a limit to the breaking elongation, so the upper limit of the breaking elongation is assumed to be 60% or less.

As with high-temperature creep properties, general methods are used to measure and evaluate room-temperature tensile properties. For example, the Japanese Industrial Standards stipulate JIS Z 2241 "Method of tensile testing of metallic materials." The fracture strain can be measured from the stress-strain curve obtained by room-temperature tensile testing.

(II-3) Technical significance of achieving both high-temperature creep properties and room-temperature tensile properties As described above, the strengthened platinum alloy according to the present invention is a platinum alloy that has creep strength in the high-temperature range as a conventional platinum alloy strengthened by dispersed particles, while having flexibility in the room-temperature range. Generally, strength and flexibility are contradictory properties, and the present invention is a platinum-based material that has a good balance of physical property values relating to both.

It is believed that these characteristics are the result of the organic interaction of multiple factors, including the dispersion of extremely fine oxides mentioned above, which improves the aspect ratio, and the state of the atomized powder produced by the suitable oxidation treatment described below. Some of these factors may be difficult to identify. Based on these considerations, the present invention applies both high-temperature creep properties and room-temperature tensile properties as the optimal method for identifying the strengthened platinum alloy of the present invention.

(II-4) Changes in physical properties based on Zr content As described above, the strengthened platinum alloy according to the present invention has a Zr content of 0.04% by mass or more and 0.25% by mass or less. By adjusting the Zr content within this range, the strengthened platinum alloy according to the present invention can obtain other physical properties or further improve the high-temperature creep properties while maintaining the above-mentioned high-temperature creep properties and room-temperature tensile elongation.

A strengthened platinum alloy with a Zr content of 0.04% by mass or more and 0.12% by mass or less can obtain flexibility at high temperatures in addition to flexibility at room temperature. Specifically, flexibility at high temperatures refers to an increase in creep strain rate. Creep strain rate is the rate of deformation (strain) over time (dε/dt) when a material undergoes creep deformation. Creep strain rate is related to the ability to absorb thermal stress and convert it into deformation, and is an index that can also be called the stress relaxation rate. By using a material with a high creep strain rate and easy stress relaxation, cracking and breakage due to thermal stress can be suppressed.

In the strengthened platinum alloy according to the present invention, when the Zr content is 0.04% by mass or more and 0.12% by mass or less, the creep strain rate in a high-temperature creep test at 1400°C and a stress of 20 MPa is preferably 1×10 ⁻⁵ %/sec or more. More preferably, it is 3×10 ⁻⁵ %/sec or more. In this way, by increasing the creep strain rate, a strengthened platinum alloy can be obtained in which cracking and fracture are further suppressed against thermal stress in the high temperature range. In particular, this creep strain rate regulation is useful in cases where repeated thermal stress is applied, and it is expected to improve resistance to thermal fatigue. It is preferable to set the upper limit of this creep strain rate to 1×10 ⁻³ %/sec or less. If the creep strain rate is too high, it may exceed the absorption of thermal stress, and high-temperature deformation may occur instead of normal creep deformation.

On the other hand, in the present invention, a strengthened platinum alloy with a Zr content of more than 0.12 mass% and not more than 0.25 mass% can have higher high-temperature creep strength. In the present invention, it is assumed that the creep rupture time in a high-temperature creep test at 1400°C and a stress of 10 MPa is 100 hours or more, but by increasing the Zr content to more than 0.12 mass%, the creep rupture time is increased beyond this prerequisite. Specifically, a rupture time of 500 hours or more can be obtained under a load of 10 MPa.

However, for the strengthened platinum alloy of the present invention having a Zr content of more than 0.12% by mass and not more than 0.25% by mass, it is preferable to set the load (stress) as the criterion for the high-temperature creep properties (creep rupture time) to 20 MPa. This is because when calculating the rupture time of a strengthened platinum alloy with high high-temperature creep properties based on a creep curve, if the stress is set to 10 MPa, the value may become too large and accurate judgment may not be possible. The high-temperature creep properties of the strengthened platinum alloy of the present invention having a Zr content of more than 0.12% by mass and not more than 0.25% by mass are preferably such that the creep rupture time in a high-temperature creep test at 1400°C and a stress of 20 MPa is 20 hours or more. In this way, the strengthened platinum alloy with an increased Zr content in the present invention has flexibility and is particularly excellent in high-temperature creep properties. This strengthened platinum alloy is useful in glass manufacturing equipment and components in which strain accumulation due to processing is not considered very much and in equipment and components in which high-temperature creep strength is prioritized.

As described above, the physical properties of the strengthened platinum alloys according to the present invention differ depending on the Zr content, but all of them maintain the prerequisite high-temperature creep properties and flexibility. That is, all of the strengthened platinum alloys have a creep rupture time of 100 hours or more in a high-temperature creep test at 1400°C and a stress of 10 MPa, and a rupture elongation of 35% or more in a room-temperature tensile test. The more suitable creep rupture time in each Zr content range is 200 hours or more at a stress of 10 MPa for strengthened platinum alloys with a Zr content of 0.04% by mass or more and 0.12% by mass or less, with an upper limit of 2000 hours or less. The creep rupture time of strengthened platinum alloys with a Zr content of more than 0.12% by mass and 0.25% by mass or less is preferably 30 hours or more at a stress of 20 MPa, with an upper limit of 200 hours or less.

(III) Manufacturing method of strengthened platinum alloy according to the present invention Next, the manufacturing method of the strengthened platinum alloy according to the present invention will be described. The manufacturing method of the strengthened platinum alloy according to the present invention basically follows the powder metallurgy method, which is a conventional technology. In the powder metallurgy method, first, platinum alloy powder is manufactured from a platinum alloy that becomes a mother alloy. Then, the platinum alloy powder is oxidized to manufacture an alloy powder in which oxides are dispersed, and then, after undergoing molding and appropriate processing steps, annealing, a strengthened platinum alloy with the desired shape and physical properties (high temperature creep properties, room temperature tensile properties) is manufactured. In the conventional manufacturing process, improvements have been made, such as adding wet grinding (ball mill grinding) and subsequent degassing treatment before the oxidation treatment of the platinum alloy powder (Patent Documents 4 and 5).

As described above, in the case of conventional reinforced platinum alloys, the improvement of high-temperature creep strength is the top priority, and in the present invention, the improvement of flexibility rather than strength is the issue. From this perspective, the method of manufacturing the reinforced platinum alloy has been reviewed, and the oxidation treatment has been improved. That is, the method of manufacturing the reinforced platinum alloy according to the present invention includes the steps of manufacturing a platinum alloy powder of a platinum alloy that essentially contains 0.04 mass% to 0.25 mass% Zr as an additive element, with the balance being Pt or Pt and Rh and unavoidable impurities, heating the platinum alloy powder at 800°C to 1400°C to perform an oxidation treatment, molding the platinum alloy powder after the oxidation treatment, and annealing the molded platinum alloy ingot, and the oxidation treatment is a process of heating the platinum alloy powder in a treatment atmosphere with an oxygen content of 50% to 100% in a naturally placed state.

(III-1) Production of platinum alloy powder In the present invention, first, a platinum alloy to be a master alloy is obtained. The master alloy is a platinum alloy that essentially contains 0.04 mass% to 0.25 mass% Zr as an additive element, with the balance being Pt or Pt and Rh and unavoidable impurities. When the strengthened platinum alloy contains additive elements other than Zr (Y, Ce, etc.), the master alloy contains these other additive elements. This platinum alloy is produced by a general melt casting method for precious metals.

The method for producing platinum alloy powder from the master alloy can be a known metal powder production process such as atomization or rotating electrode method. There are no particular limitations on the method for producing platinum alloy powder by atomization, and known atomization methods such as gas atomization and water atomization can be used. The average particle size of the platinum alloy powder produced here is preferably 20 μm or more and 300 μm or less. This is to promote the oxidation of the added elements in the alloy in the oxidation treatment described below.

(III-2) Oxidation treatment of platinum alloy powder The oxidation treatment is a process for oxidizing the additive elements (Zr, etc.) in the platinum alloy powder made of platinum alloy to generate oxide particles, and is an essential process. In the present invention, the following points should be noted regarding this oxidation treatment process.

(1) Treatment state of platinum alloy powder In the present invention, the platinum alloy powder needs to be heated and oxidized in a naturally placed state in the oxidation treatment. In the present invention, the naturally placed state means a state in which platinum alloy powder in an individually independent state is placed in an oxidation treatment atmosphere without load. For example, in the degassing treatment (Patent Document 5) performed before the oxidation treatment in the above-mentioned conventional technology, the platinum alloy powder is filled into a mold and heated and sintered. In this degassing treatment, gas components adsorbed in the platinum alloy powder are desorbed, and at the same time, the platinum alloy powder is slowly sintered and solidified. The powder mass of the platinum alloy powder produced by this sintering has a low density, but the internal stress due to sintering remains. In addition, the platinum alloy powder is in a state of being bonded to each other.

The inventors' investigations have shown that when oxidizing platinum alloy powder with limited added element content as in the present invention, the above-mentioned platinum alloy powder lump cannot be oxidized to a suitable state, and a strengthened platinum alloy with the specified physical properties cannot be produced. This is because it is difficult for the processing gas (oxygen) to reach each individual powder in the platinum alloy powder lump, but it is also believed that the load due to internal stress in the platinum alloy powder is also a factor.

Therefore, in the present invention, the platinum alloy powder is oxidized in a naturally placed state. Operations that disturb the naturally placed state of the platinum alloy powder include firing accompanied by sintering as described above, and also packing the platinum alloy powder into a mold while applying pressure during the oxidation process. However, the weight of the platinum alloy powder itself does not fall under the load referred to here. A specific method of processing in a naturally placed state in the present invention involves loading the platinum alloy powder into a tray or container without applying pressure, and placing it in a heating furnace as is to perform the heat treatment.

By performing the oxidation treatment in a natural state, the gas (oxygen-containing gas) in the heat treatment device is evenly distributed throughout the platinum alloy powder, promoting the oxidation of the added elements. This causes even trace amounts of added elements in the platinum alloy to be oxidized, producing alloy powder that serves as a precursor to the strengthened platinum alloy having the unique physical properties of the present invention described above. It is also presumed that the heat treatment in a natural, unloaded state also relaxes the distortion and lattice defects contained in the platinum alloy powder. The inventors believe that this also plays a role in producing a suitable strengthened platinum alloy.

(2) Adjustment of the Oxidation Treatment Atmosphere In the production of the strengthened platinum alloy according to the present invention, it is essential that the atmosphere in the oxidation treatment has an oxygen content (oxygen partial pressure) of 50% or more. In the production of conventional strengthened platinum alloys, the heat treatment atmosphere is often an air atmosphere. In the present invention, since it is necessary to effectively oxidize the additive elements whose contents are limited, the oxygen content of the oxidation treatment atmosphere is strictly controlled. According to the investigations of the present inventors, when the oxidation treatment atmosphere is an air atmosphere in the production method of the present invention, there is a tendency for oxide particles to become coarse. The oxygen content of the oxidation treatment atmosphere is preferably 80% or more, more preferably 99% or more.

Such control of the oxidation treatment atmosphere leads to stabilization of the oxidation state of the added elements in the platinum alloy powder after treatment, and ultimately to stabilization of the properties of the strengthened platinum alloy. In particular, the strengthened platinum alloy of the present invention requires specific values for both physical properties at high temperatures and room temperature. Control of the oxidation treatment atmosphere is effective in suppressing variation in physical properties and producing a strengthened platinum alloy that can be used stably.

In the present invention, oxidation treatment is performed based on the above two characteristics. The temperature of the oxidation treatment is set to 800°C or higher and 1400°C or lower. If the temperature is lower than 800°C, oxidation of Zr and the like does not progress easily. In addition, while the oxidation of the added elements is promoted by increasing the treatment temperature, oxidation is not promoted even if the heat treatment is performed at a temperature higher than 1400°C, and there is a concern that the crystal grains of the oxide and the platinum alloy matrix will become coarse, so the upper limit is set to 1400°C. The treatment time is preferably set to 1 hour or higher and 24 hours or lower, depending on the amount of platinum alloy powder.

(3) Relationship with conventional manufacturing methods of strengthened platinum alloys In the conventional manufacturing methods of strengthened platinum alloys, some improvements have been proposed before and after the oxidation treatment of platinum alloy powder in order to improve the high-temperature creep properties. For example, additional processes such as a process of wet-milling platinum alloy powder (platinum alloy powder before and after oxidation treatment) in a solvent (water, organic solvent, or a mixed solvent of water and organic solvent) using a ball mill or the like (Patent Documents 2 and 4) and a degassing process of heating the platinum alloy powder after wet milling in a vacuum (Patent Document 5) are known. These additional processes are considered to be effective in preventing the state of the oxides of the added elements and the swelling and deformation of the material during use.

The manufacturing method of the strengthened platinum alloy according to the present invention may include these wet grinding and degassing steps, but this is not essential. In some cases, it is preferable not to carry out these additional processes. In other words, it is preferable to manufacture platinum alloy powder from the master alloy, oxidize this as it is in the natural state, and then immediately mold it. Even with such a simplified manufacturing method, it is possible to manufacture the strengthened platinum alloy according to the present invention by carrying out an appropriate oxidation treatment. Reducing the number of steps not only contributes to cost reduction by reducing the number of man-hours, but also leads to stabilization of the product characteristics.

(III-3) Molding step after oxidation treatment Then, the platinum alloy powder made of platinum alloy having oxide particles dispersed therein that has been subjected to oxidation treatment is molded to produce a platinum alloy ingot with high density. In addition, the molding step is performed to obtain a shape suitable for processing when a rolling step is subsequently performed. As a specific processing method in the molding step, hot forging can be applied. The platinum alloy powder is often turned into a powder lump by sintering due to heating caused by the above-mentioned oxidation treatment. In the hot processing, it is preferable to heat the platinum alloy powder lump to 1000°C or more and 1400°C or less for processing. It is preferable to perform hot forging a plurality of times, with heating and forging being one set.

As a specific processing method for the molding process, a hot pressing method in which compression processing and sintering are carried out simultaneously can also be applied. The conditions for hot pressing are preferably 1000°C to 1400°C and a pressure of 10 MPa or more.

The platinum alloy powder before the molding process may be preliminarily heated and pre-sintered after the oxidation treatment. However, pre-sintering is not essential because the platinum alloy powder can also be sintered by the oxidation treatment.

(III-4) Post-processing process (rolling process, etc.)
The strengthened platinum alloy after the forming process can be subjected to post-processing such as rolling as necessary to produce a strengthened platinum alloy plate material, etc. Furthermore, in order to form the alloy into a shape according to the application (the glass manufacturing device to which it is applied), further processing steps such as rolling, extrusion, and drawing can be added. These post-processing steps may involve repeating the same processing process multiple times, or may involve a combination of different processing processes. Furthermore, when processing is carried out multiple times, intermediate heat treatment may be carried out taking into account work hardening.

(III-5) Annealing process After the above forming process and after any appropriate post-processing process, the strengthened platinum alloy is heat-treated (annealed). This is to obtain a suitable material structure by developing a recrystallized structure by annealing. The conditions of the annealing process are preferably a heating temperature of 1000°C to 1500°C and a treatment time of 0.5 hours to 3 hours. The annealing process can be performed in the air, but may also be performed in a non-oxidizing atmosphere.

(IV) Uses of the strengthened platinum alloy according to the present invention The strengthened platinum alloy according to the present invention is suitable as a constituent material of various devices used in high-temperature environments. In particular, the present invention is useful as a constituent member of a glass manufacturing device for manufacturing various glass materials. As the glass manufacturing device according to the present invention, as towers and tanks capable of storing molten glass, there are melting tanks, fining tanks, stirring tanks, etc. In addition, stirrers (stirring rods) that stir molten glass in a stirring tank to perform homogenization processing are also targets. Furthermore, devices for forming molten glass and bushings (nozzles and base plates) for spinning are also targets. Particularly preferred are towers and tanks such as melting tanks that may be partially subjected to strong processing during manufacturing. However, regardless of the presence or absence of processing during manufacturing and the strength of the processing, the present invention can be widely used as a constituent material of various glass manufacturing devices. Therefore, the present invention is also applicable to trough-shaped flow paths, throats, connecting pipes, etc. through which molten glass flows.
In addition to applications other than glass manufacturing equipment, the strengthened platinum alloy according to the present invention is also useful as a constituent material for crucibles used in single crystal growth and the like.

The strengthened platinum alloy according to the present invention described above exhibits good values for both high-temperature creep properties in the high-temperature range and room-temperature tensile properties in the room-temperature range. Therefore, it has appropriate high-temperature strength and flexibility. According to the present invention, it is possible to suppress the occurrence and progression of cracks that were observed when conventional strengthened platinum alloys were used. Therefore, the present invention can contribute to the stable operation of glass manufacturing equipment, particularly molten glass melting tanks.

4 is a SEM photograph of the surface of platinum alloy powder after oxidation treatment in the first embodiment and the comparative example. 1 shows the results of observation of the cross-sectional structure of the strengthened platinum alloy of the first embodiment and the comparative example. FIG. 2 is a graph showing creep rupture curves at 1400° C. of the strengthened platinum alloy of the first embodiment (0.07% Zr) and the comparative example (0.3% Zr). FIG. 1 is a graph showing creep strain rates at 1400° C. of the strengthened platinum alloy of the first embodiment (0.07% Zr) and the comparative example (0.3% Zr). FIG. 1 shows stress-strain curves in room temperature tensile tests of the strengthened platinum alloys of the first embodiment (0.07% Zr) and the comparative example (0.3% Zr) after annealing at 1400° C. 4 is a cross-sectional photograph of the strengthened platinum alloy of the first embodiment and the strengthened platinum alloy of the comparative example after a thermal fatigue test in the first embodiment. 5 shows creep curves of various strengthened platinum alloys (Zr content: 0.01 to 0.3 mass%) according to the second embodiment. FIG. 13 is a diagram showing the measurement results of the oxygen content and the theoretical oxygen content of the strengthened platinum alloy (Zr content: 0.01% to 0.3%) according to the second embodiment. Creep curves of the strengthened platinum alloys (Pt-Zr-Y and Pt-Y) of the third embodiment

First embodiment : A preferred embodiment of the present invention will be described below. In this embodiment, a strengthened platinum alloy containing 0.07 mass% Zr as an additive element was manufactured, and its high temperature creep properties and room temperature tensile properties were evaluated. For comparison, a conventional strengthened platinum alloy (Zr content: 0.3 mass%) was manufactured and similar evaluations were performed.

[Production of platinum alloy powder (atomized powder)]
First, 50.0 g of a button-shaped Pt-12 mass% Zr alloy was prepared as a mother alloy by vacuum arc melting. This mother alloy and pure Pt were cast by vacuum melting to produce a platinum alloy rod (dimensions: φ44 mm × 260 mm) of Pt-0.07 mass% Zr. Then, an atomized powder of a platinum alloy (Pt-0.07 mass% Zr alloy) was produced by an electrode induction melting gas atomizing device using this rod as an electrode. The atomized powder of the platinum alloy produced at this time had a particle size of 300 μm or less, and all of the produced atomized powder was collected and used in the subsequent process.

[Oxidation treatment]
The produced atomized powder was put directly into a heat treatment vessel from the recovery vessel of the atomizing device without applying any particular pressure. Then, in this natural state, it was subjected to heat treatment for oxidation treatment. The oxidation treatment was performed by heating at 1300°C for 6 hours in a pure oxygen atmosphere to obtain an atomized powder made of Pt alloy with Zr oxide particles dispersed therein. The platinum alloy powder was sintered by the heating in this oxidation treatment to become a powder lump.

[Forming and rolling processes]
The platinum alloy powder lump obtained by the above oxidation treatment was taken out of the heat treatment vessel and subjected to molding by hot forging. In the hot forging process, the platinum alloy powder lump was heated to 1300°C and forged. Six sets of forging were performed. After the molding process, cold rolling was performed to produce a platinum alloy plate material with a thickness of 1 mm. During the cold rolling process, intermediate heat treatment (annealing treatment at 1250°C for 30 minutes in air) was performed and the plate material was obtained by rolling multiple times. After rolling, the platinum alloy plate material was annealed at 1400°C for 1 hour to produce a reinforced platinum alloy plate material.

Comparative Example : A button-shaped Pt-15 mass% Zr alloy (165 g) was prepared as a mother alloy by vacuum arc melting. This mother alloy and pure Pt were processed into a platinum alloy rod (dimensions: φ44 mm × 260 mm) of Pt-0.3 mass% Zr by vacuum melting. Then, atomized powder of the Pt-Zr alloy was produced in the same manner as in the first embodiment.

[Wet grinding and degassing]
In this comparative example, the atomized powder was subjected to wet pulverization and degassing treatment, followed by oxidation treatment. The atomized powder and Pt-ZrO2 alloy balls with a diameter of 5 mm were placed in an attritor pot (made of Pt-ZrO2 alloy), which is a wet pulverizer. After sealing the pot, an organic solvent (heptane) was introduced. Then, the pulverizer blade was rotated at a rotation speed of 215 rpm, and wet fine pulverization treatment was performed for about 5 hours. The platinum alloy fine powder after pulverization was dried at 120°C for 7 hours to remove the organic solvent.

The platinum alloy powder after wet milling was packed into an open carbon container (120 mm x 120 mm, depth 150 mm) and placed in a gas atmosphere furnace where it was heated and held at 1300°C for 3 hours in an argon atmosphere at atmospheric pressure for degassing treatment. As a result of the degassing treatment, the platinum alloy powder was in the form of powder lumps that did not easily crumble.

[Oxidation treatment and molding/rolling processing]
The platinum alloy powder lump solidified in the carbon container by the degassing process was subjected to an oxidation process. In this oxidation process, the platinum alloy powder lump was heated in an air atmosphere at 1300°C for 1 hour. Thereafter, the platinum alloy powder lump was subjected to hot forging and rolling in the same manner as in the first embodiment, and further subjected to an annealing process to produce a reinforced platinum alloy plate material.

Comparative observation and test [Microstructures of platinum alloy powder and reinforced platinum alloy after oxidation treatment]
FIG. 1 is an SEM photograph (magnification 10,000 times) of the surface of the platinum alloy powder (platinum alloy powder lump) after oxidation treatment in the manufacturing process of the strengthened platinum alloy of this embodiment and the comparative example. In the platinum alloy powder of the comparative example, it can be seen that rounded oxide particles (ZrO ₂ ) are connected. In the platinum alloy powder of this embodiment, fine oxide particles are dispersed in an isolated state. The difference in particle size and distribution state of the oxide particles is considered to be due to the fact that the Zr content (0.30 mass%) of the comparative example is higher than the Zr content (0.07 mass%) of this embodiment. However, these platinum alloy powders differ in the surface morphology of the platinum matrix. In the platinum alloy powder after oxidation treatment of this embodiment, steps due to surface undulations that are presumed to be the exposure of the sliding surface are seen. On the other hand, there is no such morphological change in the matrix of the platinum alloy powder after oxidation treatment of the comparative example. The inventors presume that this is due to the influence of strain and residual stress introduced during degassing treatment and wet grinding in the manufacturing process of the comparative example. It is not clear how this difference in matrix morphology affects the properties of the strengthened platinum alloy after molding and annealing. However, considering the cross-sectional structure of the strengthened platinum alloy and the results of high-temperature creep properties and room-temperature tensile properties described below, it is considered that the above differences in the platinum alloy powder after oxidation treatment have some effect.

Figure 2 shows the results of observing the cross-sectional structure of the strengthened platinum alloy of this embodiment and the comparative example. In both strengthened platinum alloys, the material structure is made up of alternating layers of leaf-shaped crystal grains with a large aspect ratio. There is no clear difference in the cross-sectional structure between the strengthened platinum alloy of this embodiment and the comparative example. The inventors believe that this cross-sectional structure of the strengthened platinum alloy of this embodiment contributes to ensuring high-temperature strength.

[High temperature creep test/room temperature tensile test]
A high-temperature creep test was performed on the strengthened platinum alloy of the first embodiment and the comparative example manufactured above. Test pieces (JIS 13B tensile test pieces) for creep tests and room temperature tensile tests were processed and collected from the plate material of the strengthened platinum alloy manufactured above. The test temperature was 1400°C, and a stress fracture (creep) test was performed at a constant load. In this embodiment, a plurality of loads (stresses) were set, and a high-temperature creep test was performed at each set load. For the strengthened platinum alloy of this embodiment, the rupture time was measured at each load of 8, 10, 12, 15, 20, and 25 MPa (n = 2). In addition, for the strengthened platinum alloy of the comparative example, a creep test was performed at 15, 20, and 25 MPa to measure the rupture time (n = 2). In addition, considering that the Zr content of the strengthened platinum alloy of the comparative example is relatively large, the load of the comparative example is set to be higher. The time to fracture at each load was plotted, and a creep curve was created by power approximation using spreadsheet software (Microsoft Excel 2010).

In addition, room temperature tensile tests (n=2) were conducted on the reinforced platinum alloys of the first embodiment and the comparative example. In the room temperature tensile tests, stress-strain curves were created and the fracture elongation was measured.

Figure 3 shows creep rupture curves (stress-rupture time) at 1400°C for the strengthened platinum alloys of the first embodiment and the comparative example. The creep rupture time at a stress of 10 MPa was 275 hours (average of actual measurements) for the first embodiment and 250 hours (average of actual measurements) for the comparative example. The strengthened platinum alloy of the first embodiment was confirmed to have sufficient high-temperature strength in terms of high-temperature creep properties (10 MPa), as the rupture time was slightly longer than that of the comparative example. Furthermore, when compared at a stress of 20 MPa, the comparative example had a higher high-temperature creep strength.

4 is a diagram showing the creep strain rate at 1400°C of the strengthened platinum alloys of the first embodiment and the comparative example. From Fig. 4, it can be seen that the creep strain rate of the strengthened platinum alloy of the first embodiment at a stress of 20 MPa was 6.83 x ^10-5 %/sec (average value), whereas the creep strain rate of the strengthened platinum alloy of the comparative example was 5.94 x ^10-6 %/sec (average value). It can be seen that the creep strain rate of the strengthened platinum alloy of the first embodiment is clearly higher than that of the comparative example.

Figure 5 shows the results (stress-strain curves) of room temperature tensile tests of the strengthened platinum alloys of the first embodiment and the comparative example. Figure 5 also shows the room temperature tensile properties (n=2) of pure platinum (99.9% Pt) melt-cast as a reference example under the same conditions. From Figure 5, the fracture elongation at the time of material fracture is 37.2% (average value) for the strengthened platinum alloy of this embodiment, 29.4% (average value) for the strengthened platinum alloy of the comparative example, and 37.8% (average value) for the pure platinum (99.9% Pt) melt material. The strengthened platinum alloy of this embodiment shows a fracture elongation equivalent to that of the melt material of the reference example. Therefore, it was confirmed that the strengthened platinum alloy of the present invention has the same flexibility as the pure platinum melt material, even though it is an alloy (oxide-dispersed alloy).

The results of the high-temperature creep test and room-temperature tensile test above confirmed that the reinforced platinum alloy of this embodiment has sufficient high-temperature creep strength comparable to that of the conventional reinforced platinum alloy (comparative example), and also has excellent elongation (flexibility) at room temperature. It was also confirmed that the reinforced platinum of this embodiment (Zr content 0.07% by mass) has a high creep strain rate at 1400°C under a stress of 20 MPa.

[Thermal fatigue test]
A thermal fatigue test was conducted on the strengthened platinum alloys of the present embodiment and the comparative example, simulating the use of a melting tank, which is a glass manufacturing apparatus. A plate material of 300 mm (L) x 100 mm (W) was cut out from the plate material produced above to prepare a test material. In the thermal fatigue test, first, electrodes for electrical heating are attached to both ends of the test material, and the test material is heated to a predetermined test temperature. Air is blown onto the center of the heated test material for a certain period of time to locally cool it. As a result, only the center portion of the test material that has expanded due to heating shrinks, generating thermal stress. Then, after the air blowing, air is blown again after a certain period of time has elapsed. This heating-cooling cycle is repeated, and the presence or absence of cracks is confirmed to evaluate the resistance to thermal fatigue. In the thermal fatigue test of the present embodiment, the test material was specifically conducted under the following conditions.
Test temperature: 1400°C
・Electricity conditions: 5V/1350A
Air blowing conditions: 6L/3 seconds Cycle conditions: 20 seconds/1 cycle

In the thermal fatigue test, under the above conditions, at the stage of 2000 or 5000 cycles, a penetrant test (PT test) was performed on the surface (air-blasted surface) of the test material, and both sides were observed to check for the presence or absence of through cracks.

As a result of the above thermal fatigue test, the strengthened platinum alloy of the comparative example had a through crack at the stage of 2000 cycles. On the other hand, the strengthened platinum of this embodiment had no through crack even at 5000 cycles. The test of the test material of this embodiment was extended to 8000 cycles, and no cracks were generated. Figure 6 shows cross-sectional photographs of the strengthened platinum alloy of this embodiment (after 2000 cycles) and the strengthened platinum alloy of the comparative example (after 2000 cycles) after the thermal fatigue test.

The results of this thermal fatigue test confirmed that the strengthened platinum alloy of this embodiment has four times more resistance to thermal fatigue in terms of number of cycles than the comparative example. This evaluation result is believed to be due to the flexibility confirmed by the room temperature tensile properties.

Second embodiment : In this embodiment, strengthened platinum alloys were manufactured with the Zr content adjusted to 0.01 mass%, 0.04 mass%, 0.10 mass%, 0.14 mass%, 0.21 mass%, and 0.30 mass%. The manufacturing process of the strengthened platinum alloy in this embodiment is the same as that of the first embodiment. That is, a platinum alloy bar containing a predetermined amount of additive elements was manufactured to produce atomized powder, and then the rod was oxidized in a pure oxygen atmosphere in a natural state. Then, the rod was hot forged, rolled, and annealed to produce a strengthened platinum alloy plate.

Then, a high-temperature creep test and a room-temperature tensile test were performed on each strengthened platinum alloy, and the physical properties were confirmed. In the high-temperature creep test, similar to the first embodiment, multiple loads (stresses) were set. Here, too, the load was set in consideration of the Zr content of the strengthened platinum alloy. For the strengthened platinum alloy with a Zr content of 0.01% by mass, tests were performed at 7, 10, and 15 MPa.
For the strengthened platinum alloy with a Zr content of 0.04 mass%, tests were performed at 10, 12, and 15 MPa. For the strengthened platinum alloy with a Zr content of 0.1 mass% or more, tests were performed at 15, 20, and 25 MPa. The room temperature tensile test method was the same as in the first embodiment. Furthermore, in this embodiment, the same thermal fatigue test (5000 cycles) as in the first embodiment was performed.

Figure 7 shows creep curves for the reinforced platinum alloys (Zr content: 0.01 mass%, 0.04 mass%, 0.10 mass%, 0.14 mass%, 0.21 mass%, 0.30 mass%) manufactured in this embodiment. The creep rupture times at stresses of 10 MPa and 20 MPa were determined based on these creep curves. The results, room temperature rupture elongation, creep strain rate (stress of 20 MPa), and results of thermal fatigue tests (presence or absence of through cracks) are shown in Table 1. In Table 1, the creep rupture times (10 MPa, 20 MPa) of each reinforced platinum alloy are given priority as actual measured values (average values), and when actual measured values were not available, they were calculated from the creep curves (Figure 7).

Referring to Table 1, the strengthened platinum alloys with a Zr content of 0.04% by mass or more have a rupture time (10 MPa) of over 100 hours in a high-temperature creep test (1400°C). Although the high-temperature strength of these strengthened platinum alloys is lower than that of the conventional strengthened platinum alloy (No. 8: Comparative Example), it can be said that they exhibit sufficient high-temperature strength. However, the strengthened platinum alloy (No. 1) with a Zr content of 0.01% by mass had a short creep rupture time of 20 hours and was inferior in high-temperature strength. In addition, this strengthened platinum alloy No. 1 exhibited high-temperature deformation behavior, and it was not possible to calculate the deformation rate as a creep strain rate. Therefore, it was confirmed that even if the Zr content is limited to 0.04% by mass or less, it is not preferable to limit it.

On the other hand, looking at the breaking elongation in room temperature tensile tests, the strengthened platinum alloy with a Zr content of 0.01% by mass had the largest breaking elongation, but even the strengthened platinum alloys with a Zr content of 0.04% by mass or more all showed a breaking elongation of 35% or more. There is little difference in the breaking elongation at room temperature due to the Zr content. Furthermore, these strengthened platinum alloys have a clearly larger breaking elongation at room temperature than the comparative examples.

The creep rupture time (10 MPa) increases with increasing Zr content. However, when the Zr content is 0.3 mass% (No. 7), the creep rupture time drops significantly in contrast to this trend. The creep rupture time in this case also exceeds 100 hours, and it cannot be said that the high-temperature strength is inferior. However, considering the tendency for strength to decrease and the risk of weldability deterioration when the amount of added elements is increased as described above, it is appropriate to assume an upper limit of Zr content of 0.25 mass%.

In addition, looking at both the creep rupture time and high-temperature creep strain rate of the strengthened platinum alloys (No. 2 to No. 6) with Zr contents of 0.04% to 0.21% by mass, the high-temperature creep strain rate is particularly high in the strengthened platinum alloys (No. 2 to No. 4) with low Zr contents (0.04% to 0.1% by mass). On the other hand, in the high Zr contents (0.14% to 0.21% by mass), further improvement in high-temperature creep strength is observed, and the creep rupture time at a stress of 20 MP is 20 hours or more. It can be said that the high-temperature creep strain rate of the strengthened platinum alloys with high Zr contents is not particularly high (although it is higher than the comparative example). From these results, it can be said that the physical properties of the strengthened platinum alloys of the present invention change depending on the Zr content. Furthermore, based on the trends in both the rupture time (10 MPa) and creep strain rate in this embodiment, when classifying the strengthened platinum alloy of the present invention based on the differences in the physical properties, the boundary should be 0.12 mass%.

However, all of the strengthened platinum alloys have sufficient high-temperature creep strength and room-temperature tensile elongation (flexibility). As a result, the strengthened platinum alloys specified in this invention did not crack in thermal fatigue tests. Therefore, the Zr content can be set taking into account the required characteristics depending on the application, etc.

[Oxygen content measurement]
Here, for the strengthened platinum alloys manufactured in the second embodiment, the oxygen content was measured for strengthened platinum alloys containing only Zr as an additive element (Zr concentration: 0.01 mass%, 0.04 mass%, 0.07 mass%, 0.10 mass%, 0.14 mass%, 0.21 mass%, 0.30 mass%). The oxygen oil content was measured using an oxygen/nitrogen analyzer (EMGA-920 manufactured by Horiba, Ltd.). Then, along with the measurement of the actual oxygen content, the theoretical oxygen content of each alloy was calculated. In calculating the theoretical oxygen content, it was assumed that all of the Zr in the alloy produced ZrO ₂ .

Figure 8 shows the measurement results of the oxygen content and the theoretical oxygen content of each strengthened platinum alloy. From Figure 8, it can be seen that the oxygen content of each strengthened platinum alloy exceeds the theoretical oxygen content. The actual oxygen content of each strengthened platinum alloy is 1.0 to 1.5 times the theoretical oxygen content. This oxygen content that is greater than the theoretical oxygen content is thought to be due in part to the increase due to the oxidation of unavoidable impurities, but even taking this into account, it can be said that the strengthened platinum alloy produced in this embodiment is in a state in which the added element (Zr) is highly oxidized.

Here, the oxygen content was measured in the same manner for the comparative example of the first embodiment (Zr concentration: 0.3 mass%), and was found to be 1090 to 1140 ppm. The strengthened platinum alloy of this comparative example also contains 1.03 to 1.08 times the theoretical oxygen content. The strengthened platinum alloy of this embodiment has a higher oxygen content ratio, but the difference is not so clear. Nevertheless, in this embodiment, there are clear differences in the physical properties (elongation at break) in room temperature tensile tests and the results of thermal fatigue tests. This is thought to be because the strengthened platinum alloy of this embodiment has improved characteristics due to factors different from those of the conventional oxide amount and particle size considerations. In the present invention, both high temperature creep properties and room temperature tensile properties are applied to identify this.

Third embodiment : In this embodiment, the influence of the addition of an additive element other than Zr was examined. Specifically, two types of strengthened platinum alloys were manufactured: a strengthened platinum alloy containing Y as an additive element together with Zr (total content of additive elements: 0.07% by mass), and a strengthened platinum alloy containing only Y instead of Zr as an additive element (Y content: 0.07% by mass). The manufacture of these strengthened platinum alloys was also similar to the first and second embodiments.

Then, high-temperature creep tests and room-temperature tensile tests were performed on each of the strengthened platinum alloys to confirm their physical properties. The methods for the high-temperature creep tests and room-temperature tensile tests were the same as those in the first embodiment.

Figure 9 shows the creep curves of the strengthened platinum alloy (No. 9) with 0.06 mass% Zr + 0.01 mass% Y added and the strengthened platinum alloy (No. 10) with 0.07 mass% Y added, both produced in this embodiment. The creep rupture time at a stress of 10 MPa was calculated based on this creep curve. The results, as well as the room temperature rupture elongation and creep strain rate (stress of 20 MPa), are shown in Table 2.

From Table 2, the strengthened platinum alloy (No. 10) containing only Y as an additive element without Zr had a creep rupture time of over 100 hours, so that the high-temperature strength was satisfactory, but the room-temperature rupture elongation was 15% lower than that of the first embodiment (No. 3). With this alloy, there is concern about the accumulation of strain during room-temperature processing. On the other hand, even when Y is added, the strengthened platinum alloy (No. 9) added together with Zr has high-temperature creep properties equivalent to those of the first embodiment (No. 3), and the room-temperature elongation is a sufficiently high value of 35% or more. From these results, Zr should be said to be an essential additive element in order to ensure both high-temperature strength and flexibility, and it is considered that the addition of Y alone is not preferable.

Then, a thermal fatigue test similar to that of the first embodiment was carried out on No. 9 strengthened platinum alloy containing Zr and Y as additive elements, which cleared the standards of the present invention in terms of high temperature strength and room temperature elongation in the above tests. Even with this strengthened platinum, no through cracks occurred even after 5,000 cycles. From this result, it was confirmed that other elements can be added in addition to Zr to the strengthened platinum alloy of the present invention.

The strengthened platinum alloy (No. 10) containing only Y as an additive element, without Zr, had a higher creep strain rate at 1200°C than the comparative example. This is presumably because the manufacturing process in this embodiment favorably oxidized the additive elements.

The present invention is a strengthened platinum alloy that has tensile properties and flexibility at room temperature while maintaining high-temperature creep properties at high temperatures. According to the present invention, it is possible to effectively suppress through cracks at the bottom of glass equipment such as molten glass melting tanks that are manufactured by intensive processing, thereby extending the operating life of the equipment. According to the present invention, it is possible to achieve stable production and supply of glass materials when manufacturing various glass materials such as optical glass and glass fiber.

Claims (7)

A strengthened platinum alloy comprising a matrix of a PtRh alloy having a Pt or Rh content of 5% by mass or more and 40% by mass or less , in which dispersed particles of an oxide of an additive element are dispersed , and the platinum alloy powder in which the oxide is dispersed is molded ,
The strengthened platinum alloy essentially contains 0.04 mass% or more and 0.25 mass% or less of Zr as the additive element, with the balance being composed of the constituent metals of the matrix, oxygen, and unavoidable impurities;
The creep rupture time in a high-temperature creep test at 1400°C and a stress of 10 MPa is 100 hours or more;
The strengthened platinum alloy is characterized in that the breaking elongation in a room temperature tensile test is 35% or more. Contains 0.04 mass% or more and 0.12 mass% or less of Zr as an additive element,
2. The strengthened platinum alloy according to claim 1, which has a creep strain rate of 3×10 ⁻⁵ %/sec to 3×10 ⁻⁴ %/sec in a high temperature creep test at 1400° C. and a stress of 20 MPa. Contains Zr in an amount of more than 0.12 mass% and not more than 0.25 mass% as an additional element,
2. The strengthened platinum alloy according to claim 1, which has a creep rupture time of 20 hours or more in a high temperature creep test at 1400° C. and a stress of 20 MPa. A strengthened platinum alloy according to any one of claims 1 to 3, further comprising at least one of Y, Ce, Sc, and Hf as an additive element, and the total content of the additive elements is 0.04 mass% or more and 0.25 mass% or less. The strengthened platinum alloy according to any one of claims 1 to 4, wherein the oxygen content of the strengthened platinum alloy is 1.0 to 2.0 times the theoretical oxygen content resulting from the oxides of the added elements. A method for producing a strengthened platinum alloy according to any one of claims 1 to 5,
A step of producing a platinum alloy powder essentially containing 0.04 mass% or more and 0.25 mass% or less of Zr as an additive element, with the balance being Pt or Pt and Rh, and unavoidable impurities;
A step of heating the platinum alloy powder at 800° C. or more and 1400° C. or less to perform an oxidation treatment;
A step of molding the platinum alloy powder after the oxidation treatment;
Annealing the formed platinum alloy ingot;
The oxidation treatment is a process for producing a strengthened platinum alloy, in which the platinum alloy powder produced in the process for producing the platinum alloy powder is heated in a treatment atmosphere having an oxygen content of 50% or more and 100% or less in a natural, unloaded state without being subjected to a crushing treatment . A glass manufacturing apparatus comprising the strengthened platinum alloy according to any one of claims 1 to 5.

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