JP2952341B2 - Heat resistant material and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel heat-resistant material and a method for producing the same. More specifically, the present invention is lightweight and excellent in heat resistance,
The present invention relates to a TiAl intermetallic compound heat-resistant material having improved oxidation resistance at high temperatures, and a method for efficiently producing the same.

[0002]

2. Description of the Related Art Titanium alloys are widely used as aircraft materials because they are light and strong and have relatively good heat resistance. However, their operating temperature limit is 673 to 873K.
However, at a temperature higher than this, there is a disadvantage that a creep phenomenon is severe at a portion where a steady stress is applied, and it is unavoidable that the application is restricted. For this reason, titanium alloys with excellent creep resistance are being developed.
Satisfactory ones have not been obtained with ordinary alloys.

In recent years, intermetallic compounds such as titanium-aluminum, nickel-aluminum, nickel-germanium, and iron-cobalt have attracted attention as heat-resistant materials. In ordinary alloys, the heterogeneous atoms occupy each lattice position of the crystal irregularly, but in the intermetallic compound, the positions occupied by the constituent atoms are specified, forming a so-called ordered structure. This leads to a unique deformation behavior of the intermetallic compound such as a strengthening phenomenon. In general, when the deformation temperature increases, the strength of the metal material decreases.However, intermetallic compounds often exhibit the so-called abnormal strengthening phenomenon, in which the strength increases with an increase in the deformation temperature up to a certain temperature range, This is one of the reasons why the intermetallic compound attracts attention as a heat-resistant material.

Among such intermetallic compounds, TiAl
Has a low specific gravity, high specific strength, and excellent high-temperature strength compared to Ni-based superalloys and cobalt-based superalloys because it contains a large amount of aluminum. It is expected as a material. In addition, it has a higher Young's modulus and lower rigidity than other titanium alloys, thereby compensating for another disadvantage of titanium alloys.

[0005] However, this TiAl intermetallic compound has poor room temperature ductility, poor machinability, and 1073K
It has the disadvantage that the oxidation resistance at high temperatures is low, which is a major obstacle in practical use. Therefore,
In order to improve the cold ductility, intensive research has been carried out so far, for example, chromium, manganese, niobium, silicon,
Such as a method of adding elements such as tin and tungsten as a third component, a method of controlling the structure using phase transformation, and a method of ultra-fine structure using powder metallurgy (mechanical alloying or quenching process). Various methods have been tried and the results are gradually paying off.

On the other hand, in order to improve oxidation resistance at high temperatures, for example, silicon, molybdenum, niobium, phosphorus,
Manganese, chromium, a method of adding an element such as yttrium as a third component, a method of heat treatment under a low oxygen partial pressure,
A method of controlling external factors such as a method of surface coating with CoCrAl or COCrAlY, a diffusion infiltration treatment method of aluminum (aluminizing treatment method), and a method of controlling internal factors of a material such as a crystal grain size, a surface state, and an internal structure. Control methods have been attempted.

However, these methods have drawbacks such as complicated operation, insufficient oxidation resistance, and deterioration of other physical properties even if oxidation resistance is obtained. It was not satisfactory.

[0008]

Under these circumstances, the present invention provides a TiAl intermetallic compound heat-resistant material which is lightweight, has excellent heat resistance, and has remarkably improved oxidation resistance at high temperatures. It was done for the purpose of doing.

[0009]

Means for Solving the Problems The present inventors have proposed TiAl
As a result of intensive studies to improve the oxidation resistance of the intermetallic compound at high temperatures, by dispersing the SiC fine particles at a specific ratio in the matrix of the TiAl intermetallic compound, the excellent properties inherent in the TiAl intermetallic compound have been obtained. It has been found that the oxidation resistance at high temperatures can be significantly improved without deteriorating the characteristics, and the present invention has been completed based on this finding.

That is, the present invention relates to a TiAl intermetallic compound.
Weight ratio of material powder to SiC powder 100: 0.5 to 1
1273K-14 consisting of a sintered body of a 00:50 mixture
Excellent oxidation resistance in the temperature range of 73K
Characteristic heat-resistant material, and ball milling TiAl
An intermetallic compound powder is formed and then 100
0.5 to 50 parts by weight of SiC powder with respect to parts by weight,
After pressure molding, under a pressure of 30 MPa or more, 1200 to 15
TiA characterized by sintering at a temperature of 00K
l Weight ratio of intermetallic compound powder to SiC powder 100:
1 consisting of a sintered body of a mixture of 0.5 to 100: 50
Excellent oxidation resistance in the temperature range of 273K to 1473K
A method for producing a heat-resistant material.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The heat-resistant material of the present invention is TiAl
SiC fine particles are dispersed in a matrix of an intermetallic compound, and the amount of SiC needs to be in the range of 0.5 to 50 parts by weight based on 100 parts by weight of TiAl intermetallic compound. If the amount is less than 0.5 part by weight, the effect of improving oxidation resistance at high temperatures is not sufficiently exhibited, and if it exceeds 50 parts by weight, the properties as a TiAl intermetallic compound may be impaired. In order to sufficiently maintain the properties as a TiAl intermetallic compound and to improve the oxidation resistance at high temperatures, it is necessary to use SiC.
Is particularly preferably in the range of 5 to 30 parts by weight based on 100 parts by weight of the TiAl intermetallic compound.

The oxidation resistance of the TiAl intermetallic compound is better than that of titanium metal, but decreases at a high temperature of 1073 K or higher. One of the causes of the low oxidation resistance is as follows.
First, the growth of TiO ₂ is due to Al ₂ O _{3 having} excellent oxidation resistance.
Is known to be significantly faster than the growth of
The basic growth mechanism of TiO ₂ is the diffusion of oxygen through the oxygen vacancies therein, thus, as in the present invention, the addition of SiC reduces the oxygen vacancy concentration in TiO ₂ , It is considered that the growth rate is slowed and Al ₂ O ₃ is easily formed, and as a result, oxidation resistance is improved.

According to the method for producing a heat-resistant material of the present invention, first, TiAl intermetallic compound powder is formed using an equimolar mixture of titanium powder and aluminum powder. The size of the titanium powder and the aluminum powder used at this time is not particularly limited, but usually has an average particle size of 10 to 200.
Those having a range of μm are used. In order to form a TiAl intermetallic compound using this powder mixture, it is advantageous to employ, for example, a mechanical alloying method. Specifically, in a suitable mill container, under reduced pressure or under an inert gas atmosphere. Next, ball milling of the powder mixture is performed. The mill container is not particularly limited, and those conventionally used in the mechanical alloying method can be used. Examples thereof include an attritor that is a high-energy stirring mill and a rotary ball mill that can be easily enlarged for mass production. Is efficient and advantageous. When the ball milling is performed under reduced pressure, the pressure is preferably 50 Pa or less, more preferably 20 Pa or less in order to prevent oxidation of the raw material powder. On the other hand, when performing in an inert gas atmosphere,
As the inert gas, for example, argon or helium, or a gas obtained by mixing a small amount of nitrogen gas with them is preferably used.

By performing ball milling sufficiently in this manner, a T having an average particle size of about 10 to 70 μm is usually obtained.
An iAl intermetallic compound powder is obtained. Next, this powder 1
After mixing 0.5 to 50 parts by weight, preferably 5 to 30 parts by weight of SiC powder with respect to 00 parts by weight, the mixture is pressure-molded into a desired shape. As the SiC powder, a heat-resistant material having excellent oxidation resistance and creep resistance can be obtained by being homogeneously dispersed in a matrix of a TiAl intermetallic compound, and from the viewpoint of economy, an average particle size of 0.5 Those having a range of ２０20 μm are preferred. Examples of the pressure molding method include, for example, a press method, an extrusion method, an isotropic compression molding method, a slip casting method, a stretching pressure method, a direct rolling method, and the like.
Any of them can be used, but among them, the press method is preferably used.

Next, the thus obtained pressure-formed body is sintered at a temperature of 1200 to 1500 K under a pressure of 30 MPa or more to produce a desired heat-resistant material. When the pressure is lower than 30 MPa or the temperature is lower than 1200 K,
Sintering may not be performed sufficiently, and a sintered body having desired physical properties may not be obtained. Further, it is not necessary to perform sintering at a high temperature exceeding 1500K, and sintering proceeds sufficiently at a temperature lower than 1500K, and when it exceeds 1500K, it becomes difficult to obtain a sintered body having desired physical properties. The sintering apparatus is not particularly limited, and an apparatus conventionally used for producing a TiAl intermetallic compound sintered body can be used. For example, a discharge plasma sintering apparatus is efficient and advantageous.

[0016]

The heat-resistant material of the present invention is obtained by uniformly dispersing SiC fine particles in a matrix of a TiAl intermetallic compound, is lightweight, has excellent heat resistance, and has good oxidation resistance at high temperatures. It is suitably used for aircraft and the like as a lightweight heat-resistant material having high specific strength.

[0017]

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example Titanium powder (purity 99.9%, particle size 150 μm or less)
And aluminum powder (purity 99.9%, particle size 150μ)
m or less) in a molar ratio of 1: 1.
2 g was placed in a stainless steel (SUS304) cylindrical mill container having an inner diameter of 300 mm and an inner length of 350 mm in a diameter of 1 mm.
2.7mm ball for ball bearing (SUJ-2)
Filled with 41.1 kg and sealed. At this time, the ball filling amount was 33% based on the volume in the mill container, and the powder / ball weight ratio was 1/50.

Next, after the mill container was evacuated with a rotary pump, high-purity argon gas was introduced, and the rotation speed was 7.43.
After rolling ball milling was performed at rad / sec (71.0 rpm) for 400 hours, the entire amount of the powder was recovered except for those that could not be recovered by adhering to the inner wall of the mill container and the ball surface. The recovered powder was sieved using a JIS standard sieve having a mesh size of 75 μm to remove unreacted coarse particles to obtain a TiAl intermetallic compound powder (sieve passing amount).

Next, the TiAl intermetallic compound powder 10
With respect to 0 parts by weight, SiC powder (purity: 99% or more, particle diameter: 2 to 3 μm) was added in a ratio of 0.5, 10 and 15 parts by weight
Each mixed powder is mixed with a centrifugal ball mill (FR
Milling was performed as follows in an argon gas according to ISCH, P-6). That is, each mixed powder was put together with five tungsten-carbide milling balls each having a diameter of 20.0 mm in a tungsten-carbide cylindrical mill container having a capacity of 80 ml, and milled in argon gas. At this time, the weight ratio between the ball and the powder was 1 / 11.7.

After milling for 3 hours, the powder was adhered to a ball and a mill container, and all powder was recovered except for those that could not be recovered. Next, the powder is filled in a carbon mold having an inner diameter of 20 mm, and is preformed at a pressure of 40 MPa. Then, a discharge plasma sintering apparatus [Sumitomo Coal Mining Co., Ltd.]
Manufactured by SPS-1020] at a pressure of 56 MPa and a temperature of 1323 to 1373K.

With respect to the sintered body thus obtained,
Phase identification by X-ray diffraction, scanning electron microscope (Scan)
Ning Electron Microcorp
e: SEM) and EDS (Energy Dispers)
The microstructure, the composition and distribution of oxides, and the like were observed by an X-ray spectrometer, and a thermogravimetric analyzer (Thermogravimeter)
ic analysis (TGA), in air,
At 1373K and 1473K temperatures, high temperature oxidation tests were performed continuously for 60 hours.

FIG. 1 shows the heating time and weight increase when the heating temperature was 1373K (solid line) and 1473K (dashed line) in the atmospheric oxidation test of a sintered body in which 15% by weight of SiC was added to TiAl. 6 is a graph showing a relationship with the graph.

From FIG. 1, it can be seen that the weight increase due to the oxidation slightly increases with the increase of the heating time and then tends to saturate. The small increase in weight due to oxidation even when exposed to the air for a long time is presumed to be due to the fact that the addition of SiC forms an Al ₂ O ₃ film with excellent oxidation resistance uniformly on the sample surface and improves the oxidation resistance. You. It is considered that this improvement in oxidation resistance is due to the role of Al ₂ O _{3 as a} kind of barrier for suppressing the oxidation of titanium and the promotion of the formation of a protective oxide film due to its large surface area against oxygen.

Comparative Example After obtaining a TiAl intermetallic compound powder in the same manner as in the example, this powder was preformed as it was in the same manner as in the example without adding SiC powder, and then sintered.
An intermetallic compound sintered body was manufactured.

Next, the TiAl intermetallic compound sintered body was subjected to a high-temperature oxidation test continuously at a temperature of 1273 K in the atmosphere for 60 hours using a thermogravimetric analyzer. FIG. 2 shows an atmospheric oxidation test of a TiAl sintered body (127
It is a graph in 3K) which shows the relationship between heating time and weight increase. From FIG. 2, as the heating time increases,
It can be seen that the weight increase due to oxidation significantly occurs.

As described above, one of the causes of the poor oxidation resistance of the TiAl intermetallic compound is that the growth of TiO ₂ is much faster than the growth of Al ₂ O ₃ . The basic growth mechanism of the TiO ₂ is because it is the diffusion of oxygen through the oxygen vacancies therein, by applying the principle of valence control of TiO ₂ when doping the valence of larger elements of titanium It can be expected that the concentration of oxygen vacancies in the Al ₂ O ₃ layer will decrease, and that the growth rate will decrease. Therefore, based on such an idea, the SiC
To form a uniform Al ₂ O ₃ layer,
Oxidation resistance could be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between heating time in air and weight increase in one example of the heat-resistant material of the present invention.

FIG. 2 is a graph showing the relationship between heating time in air and weight increase in one example of a TiAl intermetallic compound.

Claims (2)

(57) [Claims] 1. An excellent oxidation resistance in a temperature range of 1273K to 1473K which is a sintered body of a mixture of TiAl intermetallic compound powder and SiC powder in a weight ratio of 100: 0.5 to 100: 50. Characterized heat resistant material. 2. An isomorph of titanium powder and aluminum powder.
Mixture under reduced pressure or argon or helium
Is an inert gas atmosphere mixed with a small amount of nitrogen gas.
Ball milling under air to form TiAl intermetallic compound powder
Then, 100 parts by weight of this powder was mixed with SiC powder.
0.5 to 50 parts by weight of powder, and after pressure molding, 30MP
a at a pressure of 1200 to 1500K
TiAl intermetallic compound powder characterized by being sintered
Weight ratio to SiC powder: 100: 0.5 to 100: 5
1273K-1473K consisting of a sintered body of a mixture of
Production of heat-resistant materials with excellent oxidation resistance in the temperature range
Construction method.