JPH03236403A - Manufacture of ti al base alloy-made machine parts - Google Patents

Abstract

PURPOSE:To manufacture Ti Al base alloy-made machine parts having excellent quality improved in ductility at room temp. and ductility at high temp. without damaging the excellent characteristic of Ti Al base alloy by executing pressu rize sintering to intermetallic compound Ti Al base alloy powder with hot isostatic pressing method and hot-working it. CONSTITUTION:The intermetallic compound Ti Al base alloy powder composed of one or more kinds of 32 - 36wt.% Al, 0.5 - 5wt.% Mo and 0.01 - 0.5wt.% B and the balance of Ti with inevitable impurities is packed into a near net shape vessel (the shape as similar to the fines bed product), and inner part in the vessel is evacuated and sealed. Successively, this vessel is charged into a hot isostatic pressurizing vessel and the pressurize sintering is executed at about 1,050 - 1,300 deg.C and about 1,500 - 2,000kg/cm<2> gas pressure for about 1 - 4hr, and the hot-working of isothermal forging, hot rolling, etc., is executed at about 800 - 1,200 deg.C. By this method, the Ti Al base alloy-made machine parts (e.g., engine valve, etc.) having high heat resistance, ductility and specific strength, are manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention improves the hot ductility of a TiA It-based alloy that is lightweight and has excellent high-temperature strength, and improves the hot ductility of TiA j! The present invention relates to a method for manufacturing mechanical parts made of base alloys, such as engine parts for automobiles, aircraft, etc.

(Prior Art) At present, 5UI
Heat-resistant steel such as I IL 5LII+ 36 is used. By reducing the weight of this pulp, it is possible to improve the performance of the engine, that is, to achieve higher output, higher rotation, and lower fuel consumption. However, the heat-resistant steel used for engine pulp has not only strength but also A high specific strength (strength/density) at eg 800'C) is essential.

For this reason, in recent years, intermetallic compound TiA mono-based alloys having the properties shown in (1) to (2) below have been attracting attention as materials for the above-mentioned mechanical parts.

■Light (specific gravity: 3.8). ■Good oxidation resistance at high temperatures. ■Excellent high temperature creep properties. ■High temperature strength and specific strength are higher than heat-resistant steels such as sun If 5U) I 36.

This TiA single-base alloy is Ll. It has a type crystal structure,
In the binary system of Ti and Al, the stoichiometric composition (Ti-
From 36% by weight Aj2), a wide solid solution range is formed on the Al side, and the third element can also be dissolved to some extent. However, TiAl-based alloys, Ni1 alloys, heat-resistant steels, and T
Since it has extremely low cold ductility and poor hot ductility compared to i-based alloys, etc., it cannot be processed by hot rolling at high strain rates. If so, the only way to manufacture it is to melt an ingot of a TiA mono-based alloy and cut it, which results in a significantly low manufacturing yield and high cost. Furthermore, since the ingot material has coarse crystal grains (several hundred microns or more), the product has poor room temperature ductility and cannot be put to practical use.

(Problem to be solved by the invention) TiA j! In order to put X-alloy engine valves into practical use, it is necessary to eliminate the above-mentioned drawbacks.

Regarding the improvement of room temperature ductility, several methods of adding a third element have been proposed.
No. 0 discloses Ti −(
30-36) wt% A4-(0,1-5.0) wt% M
In JP-A No. 63-125634, the n-alloy is Ti-(32-38)wt%A with B added as the third element.
1 (0.05 to 0.20) superposition% B alloys, and the cold ductility of these alloys has been improved to some extent even in the as-cast state. On the other hand, regarding the processing method for manufacturing mechanical parts made of TiAl-based alloy,
Japanese Patent No. 171862 discloses a two-step isothermal forging method including intermediate annealing, and this method also improves room temperature ductility and high temperature strength. However, this technology requires two-stage constant temperature forging, which requires processing time and mold costs.
TiA1! However, there are problems from the viewpoint of stable mass production of machine parts made of base alloys.

The object of the present invention is to develop a method that can improve the room temperature ductility and high temperature ductility of the TrAl-based alloy, without sacrificing the excellent properties of the TrAl-based alloy, and produce mechanical parts made of a TiAj binary alloy with excellent quality. It is about providing.

(Means for solving the problem) As mentioned above, TiAl-based alloys have poor plastic workability even in hot conditions, and cracks occur during hot working such as normal high strain rate hot rolling or hot forging. do.

Therefore, the present inventors proposed near net shape (
Using a powder metallurgy method that can produce a sintered body with a shape close to that of the final product, TiA I! We considered manufacturing machine parts made of base metal, and as a result of conducting detailed studies, we obtained the following knowledge. That is, (a) When TrAl-based alloy powder is used and pressure sintered using hot isostatic pressure, the resulting sintered body is fine and free of segregation. It has a II structure and has excellent permanent ductility, hot ductility, and strength.

(b) Since the sintered body has a fine structure and good hot ductility, hot working at a high strain rate is possible, and the structure is further refined, so the cold ductility is further improved.

(C) If the powder is subjected to cold working before hot isostatic pressing and sintering, the &[l texture of the sintered body becomes finer than when cold working is not performed.

(dl Ti containing an appropriate amount of one or two of Mo or B
If a powder of A-1 alloy is used, the permanent ductility and hot workability are further improved.

The gist of the present invention based on the above knowledge is the following (1) to (6).

(1) A method for producing mechanical parts made of a TiAl-based alloy, which comprises sintering powder of an intermetallic compound TiAl-based alloy using a hot isostatic pressure method, and subjecting the sintered body to hot working.

(2) A method for producing a machined part made of a TiAl-based alloy, characterized in that a diffusion heat treatment is performed after the hot working described in (1) above.

(3) Intermetallic Compound TiAl-based alloy made by cold-working powder of TiA-based alloy and press-sintering the final product using hot isostatic pressure to form a sintered body. Method of manufacturing mechanical vibration parts.

(4) A method for manufacturing a mechanical component made of a TiAl-based alloy, which comprises subjecting the sintered body described in (3) above to hot working.

(5) A method for manufacturing a TiAl-based alloy mechanical component, which comprises subjecting the sintered body described in (3) above to hot working and diffusion heat treatment.

(6) Powder of intermetallic compound TiA 14 alloy is 32~
36% AI! , and 0.5 to 5 wt% hO and 0.01 to 0.5 wt% B tm or two,
(1), (2), (3), and (4) above, characterized in that the remainder has a chemical composition consisting of Ti and unavoidable impurities.
Or the method for manufacturing a mechanical component made of a TiAj binary alloy according to (5).

(effect) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic process diagram showing a method for manufacturing a TiAl-based alloy mechanical component of the present invention.

The powder of the intermetallic compound TiA 1-based alloy, which is the starting material, is melted into an ingot by arc melting, plasma arc melting, vacuum arc melting, etc.
It can be manufactured by pulverizing it into a fine powder using the P method, atomization method, pulverization method, or the like.

The powder thus obtained is processed into steps 1 to 5 shown in FIG.
It is formed into a mechanical part of a predetermined shape, for example, an engine valve, by following any of the following steps.

Hereinafter, the case of manufacturing an engine valve will be explained as an example.

Step 1 is the manufacturing method of the first invention of the present application. Prior to hot isostatic pressurization g (tzp treatment), the powder is filled into a container whose interior has a shape similar to an engine valve, and the inside of the container is evacuated and sealed. At this time, it is best to use a container made of iron-based materials, such as ordinary steel. Containers made of iron-based materials are not only inexpensive, but also have good lubricant adhesion.
When hot working is performed after hot isostatic pressing sintering, if the hot working is performed with the container attached, good lubricity can be obtained, making the working easier. Furthermore, if the container is made of iron-based material, this can be easily removed by acid or mechanical processing in a subsequent process.

In hot isostatic pressing sintering, a container filled with powder is placed in a hot isostatic pressing device and sintered at high temperature and pressure. In this hot isostatic pressure sintering, even if the process is performed at low temperature and high gas pressure, TiA j! The base alloy powders may not bond well with each other, leaving small cavities inside, and processing at excessively high temperatures will coarsen the grains and deteriorate the standing and hot ductility, as well as the powder and container. These reaction products, for example, in the case of containers made of iron-based materials, TiFe reaction products increase and the product yield decreases. Therefore, hot isostatic pressing sintering is 10
1500-2000kg/at a temperature of 50-1300°C
It is preferable to carry out the process at a gas pressure of 1.5 cm". In addition, as for the treatment time, it is advisable to shorten the time, otherwise the powder may not sinter together sufficiently, and if it is too long, the reaction between the powder and the container will be intense.
Since the reaction product becomes thick, it is desirable to wait for about 1 to 4 hours.Incidentally, if the treatment is performed at a temperature of 1200°C for 1 hour, the Ti-Fe reaction product with a thickness of about 50 μm will form a sintered body in the case of an iron-based container. Although it is formed on the surface portion, as long as the thickness is around this level, it will not cause any particular problem in the subsequent process.

Next, the sintered body is subjected to hot processing such as isothermal forging and hot rolling, and the sintered body obtained by hot isostatic pressing sintering has a fine gI structure with little segregation and has high ductility. It is. For this reason,
High strain rate hot working is possible. With conventional melted lumber, 1
Cracks occur when hot worked at a strain rate of 0-'/sec, but in the case of a sintered body, no cracks occur even when hot worked at a strain rate higher than this strain rate, for example, 10/sec. However, even though high-speed coal hot working is possible, cracks may occur in the TiAl-based alloy if the working temperature is too low, and the life of the mold will be shortened if the working temperature is too high. A temperature of 800 to 1200°C is suitable.

Through hot working, the structure of the sintered body becomes finer due to the forging and stretching effect, and the permanent ductility improves.

This hot working can be applied to the entire sintered body, but in the case of engine valves, it is effective to apply it only to the boundary between the valve head and the shaft, where fatigue failure is likely to occur. .

After hot processing, the sintered body is machined to form an engine valve. At this time, if the sintered body is hot-processed with the container attached or has been subjected to the diffusion heat treatment described below, the container and reaction products are removed and the engine valve is finished. Finish into a valve.

Thereafter, if necessary, heat treatment may be performed at a temperature of 900-1200'C for several hours in order to remove residual stress caused by machining.

Step 2 is a manufacturing method according to the second invention of the present application, and this method is characterized in that a diffusion heat treatment is performed after the hot working. The purpose of this diffusion heat treatment is to homogenize the component elements, but it has the effect of removing processing distortion and uniforming the variation in crystal grain size caused by the difference in processing degree. Further, the grain size can also be adjusted by this heat treatment.

The diffusion heat treatment is desirably performed at a temperature similar to that of the residual stress removal heat treatment for a long time, for example, 20 hours.

After the diffusion heat treatment, the final product is finished by machining, and if necessary, heat treatment may be performed to remove the residual stress produced by the 8g machining.

Step 3 shows the manufacturing method of the third invention, step 4 shows the fourth invention, and step 5 shows the manufacturing method of the fifth invention. A feature of the third to fifth inventions is that the powder is subjected to cold working before being subjected to hot isostatic pressing and sintering.

By applying plastic strain to the powder by cold working, the sintered body becomes fine recrystallized grains due to the effect of the plastic strain during hot isostatic pressure sintering.

The final cold working can be carried out, for example, by the upsetting method after the powder is made into a compact, but in order to ensure sufficient processing distortion, the degree of processing must be approximately 20% or more in terms of bulk specific gravity. After cold working, which is desirable, it is pulverized and powdered again, followed by hot isostatic pressing and sintering.

The sintered body after hot isostatic pressure sintering has finer &[I weave and superior ductility than the sintered body obtained by hot isostatic pressing sintering of powder that is not cold worked. You can immediately send it to machining to finish it into an engine valve (Step 3).
, or after hot working the entire sintered body or a specific part to further refine #Jim and improve cold ductility,
It may be sent to machining (Step 4), and after hot working, diffusion heat treatment is performed to remove residual stress, recrystallization is performed to eliminate variations in grain size, and grain size is adjusted, and then machining is performed. You can also finish it into an engine valve (Step 5)
).

In the above manufacturing method of cold working the powder, if the cold working of the powder is performed by the upsetting method, the sintered body after hot isostatic pressure sintering will have a grain size of less than 2μ. There is. Fine grains exhibit high ductility and are easy to hot work, but if the final product is made with fine grains, the product will have poor creep strength.

Therefore, in such materials, it is preferable to adjust the crystal grain size to 2μ or more in the diffusion heat treatment step.However, if the crystal grain size is increased beyond 80μ, the cold ductility decreases.

Even when the steps 3 to 5 described above are adopted, it is desirable that the hot isostatic pressure sintering, hot working, and diffusion heat treatment be performed in the same strip 1 as described above.

In the present invention, the container enclosing the powder and the reaction products formed during hot isostatic pressing sintering need to be removed at some stage. If this is done in the final machining process, these removal and finishing to the product shape can be done at the same time, and since hot working is done with the container attached, it has the advantage of increasing workability. The stage before machining, i.e. after hot isostatic pressing sintering, after hot working,
These may be removed between the hot working and the diffusion heat treatment, or after the hot working and the diffusion heat treatment.

If it is to be removed at an intermediate stage, it may be dissolved with acid. In this case, if nitric acid is used, the container and reaction product can be removed without dissolving the base material. If nitric acid is used at a concentration of 20 to 40% and the liquid salt is used at a temperature below 50°C, the container and reaction products can be removed efficiently and safely.

In the present invention, when manufacturing an engine valve according to the above process, the raw material powder contains 32 to 36% by weight of Af,
0.5-5% by weight of moths 0 and 0.01-0.5% by weight
It is preferable to use a powder having a chemical composition containing one or two types of B, with the balance consisting of Ti and unavoidable impurities.

8l: When Al is less than 32% by weight, the alloy becomes (TiAl+Ti
JA) Ti, A7 which has a two-phase structure! The volume of the phase becomes too large and high temperature strength and standing ductility are reduced. On the other hand, alloys containing more than 36% by weight of Al have poor cold ductility.

Mo and B: Mo and B have the effect of improving room temperature ductility. Shame also has the function of increasing strength. The reason why the room temperature ductility is improved by adding Mo is that Mo makes it easier to generate deformation twins and has the effect of refining grains. In Mibyo, the above effect cannot be obtained and the improvement in room temperature ductility is small.
When Mo is included in an amount exceeding 5% by weight, β phase appears and high strength decreases.

B has the effect of strengthening the grain boundaries of the TiAlW alloy, increasing the cold ductility, and refining the grains to improve the strength. If the amount is less than 0.01% by weight, these effects will not occur;
If the content exceeds 5111%, knee borides are generated,
Cold ductility is not improved.

In addition, in the present invention, in addition to the above components, Mn, Ag, V
, T containing one or more types of NbXCr in a total amount of 5% or less
rAI! You can also use the end of the 5-go plan.

The above explanation has mainly been given using the case of manufacturing engine valves as an example, but if other mechanical parts such as turbine blades and turbocharger impellers are also manufactured by the method of the present invention, they will have excellent ductility.

(Example 1) Ti 33.5%AI by Ar arc melting! , alloy ingot (diameter = 8011II, length: 200
#60 to #100 using the PREP method.
Metsch's TiA 1 was made into spherical powder. A portion of this powder was subjected to cold upsetting to a bulk specific gravity of 20%.

These powders are stored in a container made of carbon steel (JIS 5S41) (
After vacuum-sealing in a tube (50 mm old diameter x 100 mm length) and sintering under hot isostatic pressure, some parts were left as they were and others were subjected to hot extrusion processing or hot extrusion processing and diffusion heat treatment. Table 1 shows these conditions.

Next, these sintered bodies as hot isostatically sintered,
The sintered body after hot extrusion processing and the sintered body after diffusion heat treatment were machined to remove the container and the reaction product, and tensile test pieces with an outer diameter of 4 mm and a rating distance of 16+ am were cut out from them by machining, It was subjected to a tensile test.

The tensile test was carried out subcutaneously at both room temperature and 800°C to determine the tensile strength and elongation. Further 800″C x 100
A 0-hour creep test was conducted, and the breaking strength at that time was examined. These results are also listed in Table 1.

The strain rate during the tensile test was 0.5%/min from the start of the test to the time of failure.

As a comparative example, an as-cast ingot of the same precept (NFL7 in the table) and an ingot of a Ti-35%^N-0.05% B alloy within the composition range described in the above-mentioned Japanese Patent Application Laid-open No. 125634/1983 were used. (Nα8 in the table) and Ti --34,9
%A2 alloy ingot 2 to constant temperature: 1ooo°C
: Strain rate: 10-''/sec: Processing rate: Forged material by the method described in Japanese Patent Application Laid-open No. 63-125634, which was constant temperature forged at 50% (in the table, test pieces were cut from N (L9), and the same Tests were conducted.The results are also shown in Table 1.

(Hereinafter, blank spaces) Table 1 shows that the method of the present invention enables hot working, which was previously impossible, and that diffusion heat treatment improves ductility and controls grain size, which reduces creep strength. It can be seen that control is possible and that cold working of the powder further improves ductility.

(Example 2) After ingots having the alloy composition shown in Table 2 were melted and made into spherical powder, a portion of the powder was subjected to cold upsetting with a bulk specific gravity of 20%.

Next, these powders were hot isostatically pressed and sintered at 1100°C, and then hot extruded at 1000°C.

After hot extrusion processing, the container and reaction product were removed by i-wave processing, and a tensile test piece was cut out and subjected to a tensile test.

The ingot melting method, ingot size, powder size, container, test method, and test piece size were the same as in Example 1. The test results are also listed in Table 2.

(Hereinafter, blank space) From Table 2, it can be seen that products manufactured from TiAl-based alloy powders containing Mo and B have higher strength and ductility than TiAl-based alloys that do not contain these components, for example, the TiA 1 alloy in Table 1. I know it's expensive.

(Example 3) Using TiAj2 spherical powder with the same alloy composition as in Example 1,
This is carbon with an internal shape similar to an engine valve! i
ii] It was vacuum sealed in a container made of (J■S 5541) with a wall thickness of 1.0 on, and hot isostatic pressure treatment was performed under the conditions of a treatment temperature of 1200°C, 1 hour of treatment, and a gas pressure of 2000 kg/cm. After hot isostatic pressure treatment, hot forging was performed at 1000'c, and the reaction product of the container and Ti-Fe was pickled and melted with 40% nitric acid at a processing temperature of 45°C to produce an engine valve made of TiAl base alloy. Manufactured raw materials.

This material was subjected to diffusion heat treatment in a vacuum at a temperature of 1200° C. for 24 hours to achieve a &11 weave leveling, and then subjected to finishing machining to form an engine valve made of Rial 74 alloy.

After that, we set this engine valve to the valve train exhaust valve and conducted an engine test using gasoline fuel.
The rotation limit was determined. As a comparative example, the rotation limit of a conventional heat-resistant steel engine valve was also determined.

Engine test is displacement 1300c C, OHC14
A two-cylinder pulp gasoline engine was used, and four exhaust valves made of 5UH36 were replaced with the above-mentioned TiAl-based alloy pulp.

As a result, the rotation limit of the conventional heat-resistant steel engine valve was 8000 rpm, but the rotation limit of the TiAl-based alloy valve manufactured by the method of the present invention was improved to 9000 rpm. Furthermore, no cracks or the like were observed on the bulb surface, indicating good mechanical properties.

(Effects of the Invention) As explained above, according to the method of the present invention, mechanical parts made of TiAl% alloy having high heat resistance, ductility and specific strength,
For example, engine valves can be manufactured.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing the manufacturing method of the present invention.

Claims (6)

[Claims] (1) A method for producing mechanical parts made of a TiAl-based alloy, which comprises sintering powder of an intermetallic compound TiAl-based alloy using a hot isostatic pressure method, and subjecting the sintered body to hot working. (2) A method for manufacturing a mechanical component made of a TiAl-based alloy, characterized in that a diffusion heat treatment is performed after the hot working according to claim (1). (3) A mechanical part made of a TiAl-based alloy, which is characterized in that a powder of an intermetallic compound TiAl-based alloy is subjected to cold working, and the powder is pressure-sintered using a hot isostatic pressure method to form a sintered body. Production method. (4) A method for manufacturing a mechanical component made of a TiAl-based alloy, comprising subjecting the sintered body according to claim (3) to hot working. (5) A method for manufacturing a mechanical component made of a TiAl-based alloy, which comprises subjecting the sintered body according to claim (3) to hot working and diffusion heat treatment. (6) The intermetallic compound TiAl-based alloy powder is 32 to 3
6% by weight Al, 0.5-5% by weight Mo and 0.5% by weight.
Claims (1), (2), (3), (2) characterized in that it has a chemical composition containing one or two types of B in an amount of 01 to 0.5% by weight, and the remainder consisting of Ti and unavoidable impurities. 4) or the method for manufacturing a mechanical component made of a TiAl-based alloy according to (5).