JP7809740B2 - High melting Ni-based alloy containing P - Google Patents

Description

The present invention relates to a Ni-based self-fluxing alloy containing P, its atomized powder, and metal coatings and steel parts using these alloys that have excellent corrosion resistance, crack resistance, and toughness. In particular, the present invention relates to a high-melting Ni-based alloy that has a low solidus temperature, allows for low-temperature coating formation and densification, and has a structure in which P is dissolved in a γNi matrix and/or P-containing compounds are finely dispersed.

Traditionally, self-fluxing alloys include Ni-based alloys and Co-based alloys, as specified in Japanese Industrial Standard (JIS) H8303 (Self-fluxing alloy thermal spraying). These self-fluxing alloys are primarily used in surface treatments such as thermal spraying and overlay welding, and are used to form coatings with excellent corrosion and wear resistance. The hardness of these coatings is approximately 15 to 60 HRC.

When thermal spraying is performed using nickel-based or cobalt-based alloys containing flux components such as B (boron) and Si (silicon), a dense coating can be obtained by performing a fusing process after thermal spraying. The components specified in JIS H8303 require an essential content of approximately 1.0 to 4.5 mass% B and 1.5 to 5.0 mass% Si.

The fusing temperature is usually around 1000 to 1200°C. During this process, some of the easily oxidized B and Si in the alloy become _B2O3 and _SiO2 , dissolving the metal oxides in the thermal spray coating and on the substrate surface, forming a type of borosilicate glass _that floats to the surface of the thermal spray coating like slag. This flux action results in a thermal spray coating with very few oxides and pores. During this fusing process, spray particles fuse together within the thermal spray coating, resulting in a uniform structure. Furthermore, interdiffusion occurs between the substrate and the thermal spray coating during fusing, forming an alloy layer of approximately several tens of microns at the boundary, which is metallurgically bonded.

As such, self-fluxing alloys exhibit excellent wear resistance because they contain primary and eutectic oxides and carbides in their structure. They also exhibit excellent corrosion resistance in various corrosive environments, such as hydrochloric acid, sulfuric acid, hydrofluoric acid, and caustic soda.

Self-fluxing alloys are primarily used in surface treatments such as thermal spraying and build-up welding, forming coatings with excellent corrosion and wear resistance. Their hardness ranges from approximately 15 to 60 HRC. Regarding the density of the coating, the characteristics of self-fluxing alloys are described below. Specified in JIS H 8303 (Self-fluxing alloy thermal spraying), these alloys contain flux components such as B and Si in nickel-based and cobalt-based alloys. A dense coating can be obtained by performing a fusing process after thermal spraying. The JIS-specified components essentially contain approximately 1.0 to 4.5 mass% B and 1.5 to 5.0 mass% Si.

Typically, this fusing temperature is around 1000 to 1200°C, during which some of _the easily oxidized B and Si in the alloy become _B2O3 and _SiO2 , dissolving the metal oxides in the thermal spray coating and on the substrate surface, forming a type of borosilicate glass that floats to the surface of the thermal spray coating like slag. This flux action makes it easy to obtain a thermal spray coating with few oxides and pores. Furthermore, during this fusing, the spray particles fuse together within the thermal spray coating, facilitating a homogenous structure. Furthermore, interdiffusion occurs between the substrate and the thermal spray coating during fusing, forming an alloy layer of about several tens of micrometers at the boundary, facilitating metallurgical bonding.

Self-fluxing alloys contain primary and eutectic oxides and carbides in their structure, so they are generally expected to have excellent wear resistance. They are also expected to have corrosion resistance in various corrosive environments such as hydrochloric acid, sulfuric acid, hydrofluoric acid, and caustic soda.

The applicant has also developed a steel sheet with a composition consisting of P: 0.2-6.0%, B: 0.1-4.5%, Si: 0.1-5.0%, C: 0.00-2.00%, Cr: 0.0-30.0%, Mo: 0.0-9.0%, W: 0.0-18.0%, Cu: 0.0-10.0%, Mn: 0.0-10.0%, Fe: 0.0-10.0%, Co: 0.0-10.0%, Al: 0.00-0.20%, Ti: 0.00-0.20%, Zr: 0.00-0.20%, and Hf: 0.00-0.20%, where 2.3≦P%+B%+Si%≦ We have proposed a Ni-based self-fluxing alloy that satisfies the following conditions: 11.0, Mo% + W%/2≦9.0, Al% + Ti% + Zr% + Hf%≦0.20 (see Patent Application 1).

JP 2023-31420 A

JIS H8303:2010 "Self-fluxing alloy thermal spraying"

In recent years, the applications of self-fluxing alloys for surface treatment have expanded, with consideration being given to their application in a wide range of fields, including aircraft, automobiles, boilers, and agricultural machinery, where greater durability is required than in previous applications. Therefore, the required characteristics are increasing, so that they can be used in different environments in addition to their traditional applications.

Until now, it has been common to use high-melting-point substrates, typically Fe-based materials such as SUS304 (melting point 1398-1427°C) and general structural steel (melting point approximately 1580°C), and then coat them with a Ni-based self-fluxing alloy to improve corrosion resistance and wear resistance. As a result, the temperature during thermal spraying and subsequent remelting processes has had little effect on the melting and deformation of the substrate.

On the other hand, for components that require high thermal and electrical conductivity, surface treatments are also required for substrates such as Cu (melting point 1084°C), which has a lower melting point than conventional materials. However, when forming a coating using a Ni-based self-fluxing alloy on such low-melting-point substrates, the temperature of the re-melting process, as well as the temperature during application, have a significant impact on the substrate. Re-melting with conventional Ni-based self-fluxing alloys requires re-melting at around 1000-1200°C, which inevitably leads to melting and deformation of the substrate, as well as degradation of the substrate's properties due to these thermal effects.

In addition, the higher the temperature during coating application or remelting treatment, the more easily the contained B diffuses, reacting with Fe, Cr, etc. in the substrate and causing the crystallization of hard, coarse borides, which may impair the adhesion between the substrate and the coating.

In addition, the crystal grains in the stainless steel substrate become coarse, causing a decrease in strength, and can cause excessive deterioration in corrosion resistance at the interface with the Ni-based self-fluxing alloy coating.

In addition, the higher the temperature during coating and remelting treatment, the more fuel is used, resulting in a large amount of _CO2 emissions.

Furthermore, in conventional materials, B and Si crystallize hard borides and silicides, which play an effective role in improving hardness and wear resistance. However, in areas where crack resistance and high toughness are more important than hardness and wear resistance, attempts have been made to address this by lowering the Cr content, thereby suppressing the crystallization of these hard phases, using materials such as SFNi1 (15-30 HRC), SFNi2 (30-40 HRC), and SFNi3 (40-50 HRC). However, because these conventional materials only control the hardness of the hard phase crystallization, it is impossible to achieve both hardness and toughness. Furthermore, the reduction in hard phase makes it difficult to obtain other properties such as wear resistance.

To address these issues, there is a need for the development of a high-melting Ni-based alloy that can be processed and densified at lower temperatures than conventional materials and that can be used in a wider range of fields and applications.

The Ni-based self-fluxing alloy in Patent Document 1 contains P, so its solidus or liquidus temperature is low, allowing a coating to be formed by processing at a relatively low temperature, and the main part is less likely to be exposed to high temperatures. However, because the remelting heat treatment temperature remains high as before, coarse P compounds tend to form, a fine structure is not obtained, and the substrate is prone to deformation when forming the coating, so it is still not satisfactory.

The present invention aims to provide (1) a high-melting Ni-based alloy and atomized powder that, by incorporating P, has a lower solidus temperature than conventional self-fluxing alloys (JIS H 8303), allowing for easy film formation at low temperatures and subsequent heat treatment to form a dense film at low temperatures, and (2) has a structure in which P is solid-solved and/or compounds containing P are finely dispersed in a gamma Ni matrix. It also aims to provide a film using this that has excellent corrosion resistance, crack resistance, and toughness, and to provide a part equipped with such a film.

The inventors therefore focused on P, thinking that if they could create a eutectic structure at a temperature lower than the conventional Ni-Si-B ternary eutectic temperature, they might be able to lower the solidus temperature. The eutectic temperature of Ni-P is 870°C, and they thought that adding P would result in a solidus temperature that was dramatically lower than that of conventional materials (Ni-Si-B system).

It was found that by substituting P for B and Si, the material takes on a Ni-Ni ₃ P eutectic structure rather than a CrP compound, and this has resulted in a reduction of the solidus temperature by more than 100°C compared to conventional materials.

This allows processing at lower temperatures than before, solving all of the problems that arise, such as melting and deformation of the substrate during remelting processing, reduced adhesion between the substrate and the coating due to hard, coarse borides formed by the diffusion of B, reduced strength and corrosion resistance due to coarsening of the substrate's crystal grains, and increased _CO2 emissions due to increased fuel use.

Furthermore, the ability to perform low-temperature processing means that when applying a coating, for example when spraying atomized powder of the material of the present invention to form a coating, it is possible to spray at a lower temperature than before, successfully reducing the temperature not only for the remelting process but also during spraying. Furthermore, whereas there was previously a limit to the spraying distance, it is now possible to spray over longer distances, which also leads to improved handling during spraying.

By adding P, P is dissolved in the γNi matrix and/or P-containing compounds of 10 μm or less are dispersed, forming a mesh-like network structure, which improves the strength of the matrix. Furthermore, because compounds of 10 μm or less are finely dispersed in the Ni-Ni ₃ P eutectic, it is possible to maintain uniform strength in the matrix and obtain uniform hardness in the coating. This has succeeded in achieving not only wear resistance but also both hardness and toughness, which was previously difficult to achieve.

As such, there has been no previous case in which the effects of P and its organizational structure have been examined in detail.

Therefore, the first means for solving the problems of the present invention is to provide a composition containing, in mass %, P: 0.1 to 7.0%,
B: 0.0 (including 0%) to 5.0%,
Si: 0.0 (including 0%) to 5.0%
C: 0.0 (including 0%) to 2.0%,
Cr: 0.0 (including 0%) to 30.0%,
Mo, W: One or both of Mo and W are 0.0 (including 0%) to 9.0% at Mo+W/2;
Cu: 0.0 (including 0%) to 10.0%,
Mn, Fe, Co: one or more of Mn, Fe, and Co are each 0.0 (including 0%) to 10.0%;
The balance is a Ni-based alloy consisting of Ni and unavoidable impurities,
The alloy has a structure in which P is dissolved in a hard phase having a P content of 1% or less and a γNi matrix in which P is dispersed and/or a compound containing P and having a size of 10 μm or less is dispersed,
Further, it has a solidus temperature of 800°C or higher and 950°C or lower.
It is a high melting Ni-based alloy characterized by the above.
Here, the term "high melting property" means that the alloy is self-fluxing, i.e., it is an alloy that melts easily at low temperatures and is easy to process.

The second means is that the hard phase is a boride or a carbide,
The equivalent circle diameter is 20 μm or less,
The high melting property Ni-based alloy according to the first aspect is characterized in that the area ratio is 20% or less.

The third means is a high-melting Ni-based alloy according to the first or second means, characterized in that it has a liquidus temperature of 1000°C or higher.

The fourth means is a high-melting Ni-based alloy coating made of the high-melting Ni-based alloy described in any one of the first to third means.

The fifth means is the high-melting Ni-based alloy coating according to the fourth means, characterized in that the coating is in a state where it has been remelted at less than 940°C, the porosity of the coating is porosity in the remelted coating/porosity in the thermal spray coating ≦ 0.5, and the coating has a P-containing gamma Ni matrix with a network structure.

The sixth aspect is an atomized powder for forming a coating, which is made of a high-melting Ni-based alloy described in any one of the first to third aspects.

The seventh means is a part that has the coating described in the fourth or fifth means and has excellent hardness, corrosion resistance, and crack resistance.

The addition of P in the present invention allows processing at lower temperatures than conventional methods, thereby resolving a variety of issues, including melting and deformation of the substrate during remelting, reduced adhesion between the substrate and the coating due to hard, coarse borides formed by the diffusion of B, reduced strength and corrosion resistance due to coarsening of the substrate's crystal grains, and increased _CO2 emissions due to increased fuel consumption. Furthermore, the ability to perform low-temperature processing means that when applying a coating, for example, by thermal spraying the atomized powder of the material of the present invention, the coating can be sprayed at a lower temperature than conventional methods, providing the benefits of not only the remelting process but also the low temperature during thermal spraying. Furthermore, whereas conventional methods were limited in the spraying distance, it is now possible to spray over longer distances, leading to improved handling during thermal spraying.

Furthermore, by adding P, P dissolves in the γNi matrix and/or P-containing compounds of 10 μm or less are dispersed, forming a mesh-like network structure, which improves the strength of the matrix. Furthermore, because compounds of 10 μm or less are finely dispersed in the Ni-Ni ₃ P eutectic, it is possible to maintain uniform strength in the matrix and obtain uniform hardness in the coating. This not only improves wear resistance, but also achieves both hardness and toughness, which was previously difficult to achieve.

FIG. 1 is an optical microscope image showing a cross-sectional microscopic image of an as-sprayed coating formed by thermal spraying a Ni-based alloy having the composition of the present invention onto a substrate. FIG. 2 is an optical microscope image of an example of the present invention showing a cross-sectional micrograph of the coating shown in FIG. 1 after remelting treatment at less than 940°C. FIG. 3 is an optical microscope image of a comparative example showing a cross-sectional micrograph of the coating shown in FIG. 1 after remelting treatment at 940° C. or higher.

Before describing the embodiments of the present invention, we will explain the reasons for specifying the alloy components of the present invention. Note that the percentages used in the following descriptions of the components refer to mass percent.

P: 0.1-7.0%
In the alloy of the present invention, P is an essential element for lowering the solidus temperature. However, if added in an excessive amount, coarse phosphides crystallize, resulting in excessively high hardness, embrittling the coating, and making machining difficult. If added in an amount of less than 0.1%, the effect of lowering the solidus temperature is insufficient, and if added in excess of 7.0%, the liquidus temperature rises excessively. The P content is preferably more than 0.2% and less than 6.0%, and more preferably more than 0.5% and less than 5.0%.

In particular, the effect of P allows for an unprecedentedly low solidus temperature that could not be achieved by adding B or Si alone, making remelting possible at temperatures below 1000°C, even below 950°C, and even as low as the 800°C range.

Because the solidus temperature is so low, thermal spraying is possible at lower temperatures than before. This means that not only can it be applied by remelting, but it can also be applied to coatings even when the thermal energy used during coating application is reduced by 10 to 20 percent.

Furthermore, if the coating is produced under conventional application conditions, it is possible to extend the distance (spraying distance) during coating application by 1.5 times the normal distance.

Here, it is speculated that the significant effect of adding P in lowering the solidus temperature is due to the fact that the solidus temperature in the binary phase diagram with Ni is significantly lower at approximately 870°C for P, compared to approximately 1093°C for B and approximately 1143°C for Si.

Furthermore, the addition of P suppresses deterioration of corrosion resistance at the interface between the substrate and the coating. When this alloy was thermally sprayed onto SUS304 substrate, remelted, and subjected to salt spray testing, rusting at the interface was suppressed compared to conventional P-free Ni self-fluxing alloys. Microstructural observation of the interface with the substrate revealed that in conventional P-free Ni self-fluxing alloys, the B contained in the Ni self-fluxing alloy diffused excessively to the grain boundaries of the SUS304 substrate, reacting with Cr in the SUS304 to form Cr-based borides. As a result, the Cr concentration in the surrounding SUS304 matrix decreased, a phenomenon similar to the sensitization of stainless steel was observed, and corrosion resistance deteriorated. In contrast, in the P-containing alloy of the present invention, this B grain boundary diffusion was suppressed, and it is presumed that this was suppressed by P, which also diffuses to grain boundaries in the same way as B. Furthermore, grain boundary diffusion of B in P-free Ni self-fluxing alloys produces Cr and Mo borides in SUS316 base material, degrading the corrosion resistance of the surrounding base material; in mild steel base material, the Fe borides that form themselves have lower corrosion resistance than the surrounding base material.

Furthermore, P promotes densification even in as-sprayed coatings that have not been remelted. The detailed reasons for this phenomenon are unknown, but in addition to the fact that it simply has a low solidus temperature, it is thought to be due to the fact that oxides containing P, which have relatively low sublimation temperatures, gasify slightly while the alloy particles are flying at high temperatures during thermal spraying, reducing the amount of oxide in the coating. In other words, in the thermal spraying method, slight oxidation of the particles is unavoidable while the particles are flying at high temperatures, but it is thought that the effect of these oxides, which inhibits densification of the coating, is neutralized or reduced by gasification.

In addition, P improves the strength of the matrix by dispersing P-containing and/or P-containing compounds of 10 μm or less in size in the γ-Ni matrix, forming a network structure. The dark gray areas in Figures 2 and 3 correspond to the dispersed P-containing and/or P-containing compounds of 10 μm or less. Furthermore, the fine dispersion of compounds of 10 μm or less in the Ni-Ni ₃ P eutectic maintains uniform matrix strength and provides uniform hardness for the coating. This not only improves wear resistance, but also helps achieve both hardness and toughness, which was previously difficult to achieve. A uniformly hard structure with finely dispersed P compounds can be achieved, for example, by adding P and remelting the coating at a temperature lower than 940°C.

B: 0.0-5.0%
In the alloy of the present invention _{, B may be added as needed to lower the solidus temperature and reduce oxides in the coating. Part of the B and Si forms B2O3 and SiO2} , dissolving metal oxides in the thermal spray coating and on the substrate surface. This forms a type of borosilicate glass, which floats to the surface of the thermal spray coating like slag, acting as a flux, reducing oxides and pores in the thermal spray coating and increasing its density. However, excessive addition raises the liquidus temperature due to the crystallization of coarse borides. Furthermore, the formation of borides increases the hardness. Since P lowers the solidus temperature, no addition is necessary. However, adding more than 5.0% of B excessively raises the liquidus temperature, so the content is preferably less than 4.0%, and more preferably less than 2.0%.

Si: 0.0-5.0%
In the alloy of the present invention _{, Si may be added as needed to lower the solidus temperature and reduce oxides in the coating. A portion of the B and Si forms B2O3 and SiO2} , dissolving metal oxides in the thermal spray coating and on the substrate surface. This forms a type of borosilicate glass, which floats to the surface of the thermal spray coating like slag, acting as a flux, reducing oxides and pores in the thermal spray coating and increasing its density. However, adding too much Si can make the coating excessively hard, embrittling it and making it difficult to machine. Since P plays a role in lowering the solidus temperature, no addition is necessary. Adding more than 5.0% Si results in excessively high hardness, so the content is preferably less than 4.0%, more preferably less than 3.0%.

C: 0.0-2.0%
In the alloy of the present invention, C has the effect of increasing hardness and may be added as needed. However, if the amount added is too large, the coating becomes excessively hard and embrittled, and machining becomes difficult. If added in excess of 2.0%, the hardness becomes excessively high. Preferably, the C content is less than 1.8%, more preferably less than 1.6%.

Cr: 0.0-30.0%
In the alloy of the present invention, Cr has the effect of improving corrosion resistance and may be added as needed. However, if the content exceeds 30.0%, the liquidus temperature will rise excessively. Preferably, the content is less than 20.0%, more preferably less than 18.0%.

Mo+W/2: 0.0~9.0%
In the alloy of the present invention, Mo and W have the effect of improving corrosion resistance and may be added as needed. The effect of W is half that of Mo, in terms of mass percent. However, excessive addition of W increases the liquidus temperature and generates coarse phosphides containing high concentrations of Mo and/or W, resulting in excessively high hardness, embrittlement of the coating, and difficulty in machining. Addition of Mo+W/2 exceeding 9.0% excessively increases the liquidus temperature. The content is preferably less than 5.0%, more preferably less than 4.0%.

Cu: 0.0-10.0%
In the alloy of the present invention, Cu has the effect of improving corrosion resistance and may be added as needed. However, excessive addition of Cu reduces corrosion resistance. If Cu is added in excess of 10.0%, corrosion resistance will also decrease. Preferably, Cu is less than 5.0%, more preferably less than 4.0%.

Mn, Fe, Co: 0.0-10.0%
In the alloy of the present invention, Mn, Fe, and Co are elements that do not have a significant effect on the properties, and may be added up to an upper limit of 10% each.

(Organizational characteristics)
The structure is one in which P is dissolved in a hard phase containing 1% or less of P and compounds containing P with a size of 10 μm or less are dispersed in a gamma-Ni matrix. P is only present in trace amounts in the hard phase, primarily in the gamma-Ni matrix. The dispersion of P is dissolved in a solid phase and/or compounds containing P with a size of 10 μm or less (the dark gray areas in Figures 2 and 3) and these compounds form a mesh-like network, improving the strength of the matrix. Furthermore, the fine dispersion of compounds with a size of 10 μm or less in the Ni-Ni ₃ P eutectic maintains uniform strength in the matrix, resulting in uniform hardness for the coating. This not only improves wear resistance, but also enables the combination of hardness and toughness, which was previously difficult to achieve.

Solidus temperature must be between 800°C and 950°C. The addition of P lowers the solidus temperature, but the liquidus temperature varies depending on the content of Cr, B, Si, etc. If the solidus temperature exceeds 950°C, the thermal impact on the substrate during remelting processing becomes significant.

Liquidus temperature of 1000° C. or higher: The liquidus temperature of the alloy of the present invention is preferably 1000° C. or higher. If the liquidus temperature is lower than 1000° C. and the temperature range between the solidus and liquidus is very narrow, the remelting treatment conditions become difficult.

The hard phase is a boride or carbide, and its equivalent circle diameter is 20 μm or less, and its area ratio is 20% or less. If 20% or more of coarse hard phases exceeding 20 μm (the size is calculated as the equivalent circle diameter), the material becomes excessively hard, embrittling, and making machining difficult. Furthermore, since corrosion also occurs at the grain boundaries of the hard phase, if the hard phase size is less than 20 μm and its area ratio exceeds 20%, corrosion is likely to progress. On the other hand, if the hard phase size exceeds 20 μm and its area ratio is 20% or less, cracks may originate from the coarse hard phase, affecting machinability. Therefore, it is preferable that the equivalent circle diameter is 20 μm or less, and its area ratio is 20% or less.

The porosity of a coating that has undergone remelting treatment at less than 940°C must be porosity in the remelted coating/porosity in the thermal spray coating ≦0.5. Even if the solidus temperature is lowered, if the remelting treatment is performed at 940°C or higher, for example, at the conventional temperature of around 1000°C, the coating will naturally become dense (porosity: porosity in the remelted coating/porosity in the thermal spray coating ≦0.5). For example, Patent Document 1 only performs remelting treatment at 940°C, and in this case, the coating will naturally become dense (porosity: porosity in the remelted coating/porosity in the thermal spray coating ≦0.5). However, because the temperature is too high, the material melts, losing its shape and causing sagging. On the other hand, in the present invention, both the above-mentioned structure and densification can be achieved by treatment at even lower temperatures, such as below 940°C.

Comparing Figure 1, which shows the sample before remelting at low temperature, with Figure 2, which shows the sample after remelting at low temperature, it can be seen that the number of voids has decreased in Figure 2. Furthermore, if the remelting temperature is too high, a coarse structure will result, as shown in Figure 3.

(Example)
Powder preparation method: Raw materials weighed to the compositions shown in Nos. 1 to 20 in Table 1 were melted in a vacuum melting furnace and atomized with high-pressure nitrogen gas to obtain gas atomized powders. These powders were classified by sieving to obtain powders with a particle size range of 45 μm to 125 μm, and used as test powders.

Evaluation of the solidus temperature of the powder The solidus temperature of the test powder was evaluated using a thermal analyzer (DTA). Approximately 30 g of powder was used for the measurement. After evacuation, Ar gas was flowed at 200 ml/min. The powder was heated from room temperature to 1500°C at a temperature increase rate of 20°C/min and held at 1500°C for 5 minutes. After holding, the powder was cooled to room temperature at a rate of -20°C/min. The lowest temperature at which the exothermic peaks appearing in the DTA signal during cooling ended was evaluated as the solidus temperature.

Regarding the method for producing the thermal spray coating, a 50 x 50 x 9 mm SUS304 plate was used as a substrate. After blasting the 50 x 50 mm surface, the test powder was atmospherically plasma sprayed to obtain a coating. The substrate was cooled with air during the thermal spraying process. The substrate with the thermal spray coating was then placed in an electric furnace and heated in an Ar flow atmosphere to a temperature above the solidus temperature but below 940°C, as shown in Table 2 for invention examples 1 to 12. The temperature was then held for 20 minutes, and the furnace was cooled to obtain a fused coating. The coating thickness was approximately 300 μm. The remelting temperatures for the comparative examples were as shown in Table 2, and comparisons were also made at temperatures above 940°C.

Evaluation of Residual Pores and Residual Oxides in Thermal Spray Coatings Test specimens for cross-sectional observation were cut out from the thermal spray coating before remelting treatment and from the remelted coating (in the present invention, the remelting treatment was performed at a temperature above the solidus temperature but below 940°C), polished, and photographed near the center of the coating in the thickness direction at 100x magnification using an optical microscope. The total number of residual pores and residual oxides of 20 μm or more per 500 μm square was evaluated. Note that when the shape of the photographed residual pores or residual oxides was elliptical rather than circular, the number of pores with a major axis of 20 μm or more was calculated. Evaluation was performed using the value of number of remelted coatings / number of thermal spray coatings.

Regarding the corrosion resistance evaluation of thermal spray and remelted coatings, a corrosion resistance test was carried out on a cross-section of a remelted coating (in the present invention, the remelting was carried out at a temperature above the solidus temperature but below 940°C), which was cut out and polished. A salt spray test (5% NaCl, 35°C, 96 hours) was carried out, and samples in which rusting was limited to a small area on the coating and/or at the interface between the coating and the base metal were rated as A, and samples in which rusting was widespread were rated as B.

Hardness evaluation of remelted coatings: For the remelted coatings (in the present invention, the remelting was performed at a temperature equal to or higher than the solidus temperature but lower than 940°C), cross sections were cut out and polished to evaluate the Vickers hardness. The test force was 2.94 N, and the average value of five measurements was used to evaluate the hardness.

Evaluation of deformation of substrate after remelting treatment When the remelted coating (including substrate) was placed on a flat base, those that were not in contact with the base were judged to be deformed. (In the present invention, the remelting treatment was performed at a temperature above the solidus temperature but below 940°C.) Those that were in contact with the base were rated A, and those where the substrate placed on the base was not in contact with the base or was unstable and wobbly were rated B.

For the Ni-based alloys of invention examples 1 to 12, the remelting heat treatment temperatures for all of the coatings were low, at 850 to 920°C. The size of the P compounds in the coating was 10 μm or less, the circle-equivalent diameter of the hard phase, which contained almost no P, was 20 μm or less, and the porosity of the coating was 0.5 or less in all cases, resulting in a structure with finely dispersed P. Coatings with excellent corrosion resistance and substrate deformation evaluation were obtained. Furthermore, the P content of the hard phase in the invention examples was approximately 0.04 to 0.09%, and P in the hard phase was 1% or less, as determined by SEM/EDS analysis. Therefore, uniform strength of the matrix, uniform hardness of the coating, and a balance of hardness and toughness were achieved.

In Comparative Example No. 13, P was not added to the Ni-based alloy, and the solidus temperature was high, so the remelting heat treatment temperature was also high, and deformation of the substrate was observed.
In Comparative Example No. 14, P was excessive, coarse P compounds were crystallized, and deformation of the substrate was also observed due to the high remelting heat treatment temperature.
Comparative Example No. 15 contained excessive amounts of P and Cu, and was therefore inferior in corrosion resistance. Deformation of the substrate was also observed.
In Comparative Example No. 16, the coating was too hard due to the excess B, Si, and C, coarse P compounds were observed, the corrosion resistance was poor, and deformation of the substrate was also observed.
In Comparative Example No. 17, the Cr content was excessive, the liquidus temperature was elevated, coarse P compounds were observed, the corrosion resistance was poor, and deformation of the substrate was also observed.
In Comparative Example No. 18, P was not added to the Ni-based alloy, and the solidus temperature was high, so the remelting heat treatment temperature was also high, and deformation of the substrate was observed. In addition, the total amount of Mo and W and the total amount of Mn, Fe, and Co were all excessive, so the liquidus temperature was excessively high, and the hardness of the coating was too high, resulting in poor corrosion resistance.
In Comparative Examples 19 and 20, the remelting heat treatment temperature was as high as 940° C., so coarse P compounds were observed and deformation of the substrate was also observed.

The present invention can lower the remelting heat treatment temperature of thermal spray coatings, so in addition to the applications where Ni-based self-fluxing alloy thermal spray coatings have traditionally been used, it can also be widely applied to fields such as aircraft, automobiles, boilers, and agricultural machinery.

Claims (8)

P in mass%: 0.1 to 7.0%,
B: 0.0 (including 0%) to 5.0%,
Si: 0.0 (including 0%) to 5.0%
C: 0.0 (including 0%) to 2.0%,
Cr: 0.0 (including 0%) to 30.0%,
Mo, W: One or both of Mo and W are 0.0 (including 0%) to 9.0% at Mo+W/2;
Cu: 0.0 (including 0%) to 10.0%,
Mn, Fe, Co: one or more of Mn, Fe, and Co are each 0.0 (including 0%) to 10.0%;
The balance is a Ni-based alloy consisting of Ni and unavoidable impurities,
The alloy has a structure in which P is dissolved in a hard phase having a P content of 1% or less and a γNi matrix in which P is dispersed and/or a compound containing P and having a size of 10 μm or less is dispersed,
Further, it has a solidus temperature of 800°C or higher and 950°C or lower.
A highly meltable Ni-based alloy characterized by: The hard phase is borides and carbides,
The equivalent circle diameter is 20 μm or less,
2. The high melting property Ni-based alloy according to claim 1, wherein the area ratio is 20% or less. The high-melting Ni-based alloy according to claim 1 or 2, characterized by having a liquidus temperature of 1000°C or higher. A high-melting Ni-based alloy coating made from the high-melting Ni-based alloy according to claim 1 or 2. A high-melting Ni-based alloy coating made from the high-melting Ni-based alloy described in claim 3. A coating in a state that has been remelted at less than 940°C, wherein the porosity of the coating is such that the porosity in the remelted coating/the porosity in the thermal spray coating is ≦0.5;
Furthermore, the coating has a network structure of a γNi matrix containing P.
The high melting property Ni-based alloy coating according to claim 5, characterized in that A part having excellent hardness, corrosion resistance, and crack resistance, which has the coating described in claim 5. A part having excellent hardness, corrosion resistance, and crack resistance, which has the coating described in claim 6.