JPH0517836A - Tial-base alloy excellent in hardness at high temperature as well as in strength at high temperature and its production - Google Patents

Abstract

PURPOSE:To provide a TiAl-base alloy having superior strength at high temp. and hardness at high temp. by constituting a TiAl-base alloy of respectively specified weight percentages of Al and N and the balance Ti. CONSTITUTION:The TiAl-base alloy has a composition consisting of, by weight, 33-36% Al, 0.01-0.10% N, and the balance Ti with inevitable impurities, or, a material consisting of 33-36% Al and the balance Ti with inevitable impurities is used and a nitride of <=1600 deg.C melting point is added to this material, followed by refining. By this method, the TiAl-base alloy excellent in hardness at high temp. as well as in strength at high temp. can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a TiAl based alloy excellent in high temperature strength and high temperature hardness and a method for producing the same.

[0002]

2. Description of the Related Art TiAl-based alloys, which are intermetallic compounds, are expected as next-generation heat-resistant materials because they not only have a low specific gravity of 3.7, but also have excellent high-temperature strength.
However, there are some problems to be overcome in order to put this heat-resistant material into practical use. 1. The high temperature strength is not always superior to that of conventional heat resistant materials. That is, the TiAl-based alloy has the same strength as that at room temperature up to around 800 ° C, but its value is not necessarily high.For example, when subjected to homogenizing heat treatment at a temperature of 1,100 ° C, the yield strength is at most 35 kg / It is about mm ² . Even if we compare the specific strength of TiAl-based alloys at 800 ℃ to Ni-based superalloys, it cannot be said that TiAl-based alloys have a clear advantage, but rather Ni-based superalloys are more ductile at room temperature. Considering the advantages, the conventional TiAl-based alloy is Ni
It is unlikely to replace the base superalloy. Therefore, TiAl
In order for the base alloy to retain its superiority as a heat resistant material, it is necessary to further improve the specific strength at high temperatures.

2. Insufficient wear resistance at high temperature. That is, as a target of use of the TiAl-based alloy that is lightweight and has excellent heat resistance, for example, a moving part of an automobile engine or an aircraft engine can be considered. Reducing the weight of moving parts in the engine can significantly improve engine efficiency. As moving parts of an engine, there are, for example, intake and exhaust valves, but these kinds of parts are required to have wear resistance at high temperatures. However, the wear resistance of TiAl-based alloys at high temperatures cannot be said to be sufficiently high. For example, the high-temperature hardness of Ti-34% Al at 800 ° C is about 170 at the Vickers hardness under a load of 1 kg, which is not sufficient.

In order to solve the above-mentioned problem 1, the following TiAl-based alloy has been proposed. 1. JP-B-62-215 discloses that 30 to 36 wt.% Al and 0.1
To 5.0 wt.% Mn and TiAl with excellent high temperature strength
A base alloy (hereinafter referred to as Prior Art 1) is disclosed. 2. Japanese Patent Application Laid-Open No. 1-298,127 discloses the following TiAl-based alloy having excellent high temperature strength. Ie, 30 to 36
A TiAl-based alloy containing wt.% Al and 0.5 to 15 wt.% Nb, a TiAl-based alloy containing 0.01 to 0.5 wt.% B, C, Si at least one, 30 to 36 wt. % Al and 0.5 to 15
A TiAl-based alloy containing wt.% Nb and 0.1 to 4.0 wt.% Cr, a TiAl-based alloy containing 0.01 to 0.5 wt.% B, C and Si at least one, 30 to 36 wt. % Al and 0.5 to 15
A TiAl-based alloy in which wt.% Nb and 0.1 to 6.0 wt.% Mo are added, and a TiAl-based alloy in which 0.01 to 0.5 wt.% B, C, or Si is added at least are disclosed. (Hereinafter referred to as Prior Art 2). 3. Japanese Unexamined Patent Publication (Kokai) No. 2-258,939 discloses a TiAl-based alloy containing 38 to 62 atomic% of Al and 0.12 to 10 atomic% of N 2 (hereinafter referred to as prior art 3).

[0005]

However, the above-mentioned prior arts 1 and 2 contain a large amount of elements having a larger specific gravity than Ti, so that the lightness, which is the greatest feature of TiAl-based alloys, is impaired. Moreover, Prior Art 2 does not necessarily have an advantage over the conventional TiAl-based alloy in view of the manufacturing cost, because an extremely expensive element is added. Although the prior art 3 is included in the scope of the present invention, the lower limit of the N content of the example disclosed in Japanese Patent Application Laid-Open No. 2-258,939 is 0.5 atomic% which exceeds the upper limit of the N content of the present invention.
That is, it is 0.18 wt.%. That is, JP-A-2-258,939 does not describe TiAl-based alloys within the scope of the present invention. Moreover, Japanese Patent Application Laid-Open No. 2-258,939 does not describe any high temperature characteristics. From such a thing,
The development of TiAl based alloys with excellent high temperature strength and high temperature hardness is strongly desired, but such alloys have not yet been proposed. Therefore, the object of the present invention is
2% proof stress 40 kgf / mm ² or more, a tensile strength of 45 kgf / mm ² or more, yet, more than 200 in Vickers hardness hardness load 1kg at 800 ° C., to provide an excellent TiAl based alloy high-temperature strength and high temperature hardness Especially.

[0006]

The first aspect of the present invention is characterized in that Al: 33 to 36 wt.%, N: 0.01 to 0.10 wt.%, And the balance: Ti and inevitable impurities, And the second aspect of the present invention
Is characterized by using a material consisting of Al: 33 to 36 wt.%, And the balance: Ti and unavoidable impurities, adding a nitride with a melting point of 1,600 ° C or less to the above material, and melting it. It is a thing.

Next, excellent in high temperature strength and high temperature hardness,
The reason why the chemical composition of the TiAl-based alloy of the present invention is limited to the above range will be described. (1) Aluminum (Al) Aluminum has the strength and hardness of a TiAl-based alloy. However, the aluminum content is 33w
If it is less than t.%, the hardness is improved but the ductility is remarkably reduced. On the other hand, when the aluminum content exceeds 36 wt.%, Both strength and hardness decrease. Therefore, the aluminum content should be limited to the range of 33 to 36 wt.%.

(2) Nitrogen (N) Nitrogen improves the strength and hardness of the TiAl-based alloy. However, if the nitrogen content is less than 0.01 wt.%, The desired effect cannot be obtained in the above-described action. On the other hand, if the nitrogen content exceeds 0.10 wt.%, Not only does the hardness not improve,
Ductility deteriorates significantly. Therefore, the nitrogen content should be limited to the range of 0.01 to 0.10 wt.%.

To produce the TiAl-based alloy of the present invention, A
l: 33 to 36 wt.%, and balance: Ti and inevitable impurities are added to the material and nitrided. Examples of nitrides include TiN and AlN. But,
Since the melting points of these nitrides are very high, it takes a long time for melting, and the operation maintenance cost of the melting apparatus increases. Moreover, since these nitrides remain unmelted in the TiAl-based alloy, the target TiAl-based alloy having high-temperature strength and high-temperature hardness cannot be obtained.

To solve such a problem, a nitride whose melting point is close to that of the TiAl-based alloy may be used. Therefore, in order to produce the TiAl-based alloy of the present invention, it is necessary to use a nitride having a melting point of 1,600 ° C. or less even in consideration of overheating during melting. As the nitride having a melting point of 1,600 ° C or less, nitrogen in the range of 0.01 to 0.10 wt.% Can be added to the TiAl-based alloy, and elements other than Ti and Al such as manganese nitride and chromium ferronitride can be added. It may be contained.

[0011]

Next, the present invention will be further described with reference to examples. TiAl-based alloy materials, manganese nitride, and ferro-chromium nitride were placed in a non-consumable electrode arc melting furnace to melt, and alloys No. 1 to 7 of the present invention having the composition shown in Table 1, and
Comparative alloys No. 8 to 15 were produced. Next, Ti from No. 1 to 15
Cast an Al-based alloy ingot and heat the ingot at 1,100 ° C.
Was heated for 4 hours. Then, a tensile test piece having an outer diameter of 4 mm and a gauge length of 20 mm and a Vickers hardness test piece having a size of 5 × 5 × 10 mm were cut out from each ingot. The tensile test was carried out at room temperature and 800 ° C., respectively. The crosshead speed at room temperature was 0.15 mm / min, and at 800 ° C the crosshead speed was 0.5 mm / min. The Vickers hardness test was carried out under the conditions of a load of 1 kg and a load time of 10 seconds at room temperature and 800 ° C., respectively. The Vickers hardness test at a temperature of 800 ° C. was performed in vacuum.

Table 2 also shows the results of the tensile test and the Vickers hardness test of the alloys of the present invention and the comparative alloys.

[Table 1]

[0013]

[Table 2]

As is clear from Table 2, alloy No. 1 of the present invention
Nos. 7 to 7 have a 0.2% proof stress at 800 ° C of 40 kgf / mm ² or more,
Tensile strength at 800 ℃ 50kgf / mm ² or more, and 80
The hardness at 0 ° C. is 200 or more, and it can be seen that it has excellent high temperature strength and high temperature hardness. In contrast, comparative alloy No.8 from 11, 14 and 15, 0.2% proof stress is less than 40 kgf / mm ² at 800 ° C., a tensile strength of less than 50 kgf / mm ² at 800 ° C., and the hardness at 800 ° C. Is 200
And is inferior in high temperature strength and high temperature hardness. In contrast, Comparative Alloys Nos. 12 and 13 have excellent high-temperature strength and high-temperature hardness, but have a high N content,
Poor elongation at 0 ° C.

[0015]

As described above, according to the present invention, a useful effect that a TiAl-based alloy having excellent high temperature strength and high temperature hardness can be obtained is brought about.

Claims (2)

[Claims] 1. A TiAl-based alloy excellent in high temperature strength and high temperature hardness, characterized in that Al: 33 to 36 wt.%, N: 0.01 to 0.10 wt.%, And the balance: Ti and inevitable impurities. 2. A material comprising Al: 33 to 36 wt.% And the balance: Ti and unavoidable impurities is used, a nitride having a melting point of 1,600 ° C. or less is added to the material, and the material is melted. A method for producing a TiAl-based alloy excellent in high temperature strength and high temperature hardness.