JPH0565561A - Production of tial intermetallic compound having high creep strength - Google Patents

Abstract

PURPOSE:To obtain a TiAl intermetallic compd. having enhanced creep strength as well as an upward tendency in strength at ordinary temp. CONSTITUTION:Stock having 0.1-0.5 atomic Ge content and lamellar structure L formed by alternately laminating TiAl phase p1 and TiAl phase p2 is produced and heat-treated to increase the average width (W1) of the TiAl phase-p2 in the laminating direction while inhibiting the increase of the average grain diameter (d) of the lamellar structure L.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a TiAl-based intermetallic compound having high creep strength.

This type of TiAl-based intermetallic compound has been attracting attention as a structural material for engine parts and the like because it is lightweight and has excellent heat resistance.

[0003]

2. Description of the Related Art Conventionally, as the TiAl intermetallic compound, one having a layered structure in which Ti ₃ Al phase (α ₂ phase) and TiAl phase (γ phase) are alternately laminated is known.

[0004]

It is known that in conventional TiAl intermetallic compounds, the average grain size of the layered structure may be increased by heat treatment or the like in order to improve the creep strength. However, there is a problem that such expansion of the layered structure causes a decrease in the room temperature strength of the TiAl-based intermetallic compound on the other hand.

In view of the above, the present invention provides a control of the metal structure by heat treatment using a specific third element,
It is an object of the present invention to provide the above-mentioned manufacturing method capable of obtaining a TiAl-based intermetallic compound having an increased tendency of room temperature strength and an improved creep strength.

[0006]

The method for producing a TiAl-based intermetallic compound having high creep strength according to the present invention comprises:
A material having a layered structure in which i ₃ Al phases and TiAl phases are alternately laminated and having a Ge content set to 0.1 atomic% ≤ Ge ≤ 0.5 atomic% is manufactured, and A heat treatment is performed to suppress an increase in the average grain size of the layered structure, and T in the stacking direction of the Ti ₃ Al phase and the TiAl phase.
It is characterized in that the average width of the iAl phase is expanded beyond the average width of the material.

[0007]

EXAMPLE FIG. 1 shows a model of the metallic structure of the material. The metallic structure is Ti ₃ Al phase (α ₂ phase) p1 and T.
It is composed of an aggregate of layered structures L in which iAl phases (γ phases) p2 are alternately laminated.

The material is Ge containing the main component of the TiAl-based intermetallic compound, and the main component is 36.
The composition is such that atomic% ≦ Al ≦ 60 atomic% and the balance Ti, and the Ge content is 0.1 atomic% with respect to the main component.
≦ Ge ≦ 0.5 atomic% is set.

FIG. 2 schematically shows the metallographic structure of the TiAl-based intermetallic compound obtained by subjecting the material to heat treatment. The metallographic structure is composed of an aggregate of layered structures L like the material, but Ti in each layered structure L
The morphology of the Al phase p2 is different from the material.

That is, Ti₃Al phase p1 and TiAl phase p2
Average width w of the TiAl phase p2 in the stacking direction with₁Primitive
Average width w of TiAl phase p2 of the material₂Is extended than
(W ₁> W₂).

On the other hand, the average grain size d of each layered structure L in the stacking direction is suppressed so as to be substantially the same as the average grain size d of the material.

Such control of the metal structure is achieved by heat-treating with a small amount of Ge as described above.

As described above, the average grain size d of each layered structure L
The average width w ₁ of the TiAl phase p2 while suppressing an increase in
When the material is expanded beyond that of the material, the room temperature strength of the TiAl-based intermetallic compound can be maintained in an increasing tendency and the creep strength can be improved.

However, if the Ge content is Ge <0.1 atomic%.
In that case, it is not possible to control the metal structure as described above,
On the other hand, when Ge> 0.5 atomic%, a large amount of precipitates are generated at the grain boundaries, so that the room temperature strength and the creep strength are rapidly reduced.

Next, a specific example will be described. (A) Ti (sponge titanium) having a purity of 99.5%,
Al (aluminum shot) with a purity of 99.99%,
Ge (strips) with a purity of 99.999%, in atomic%,
(Ti ₅₃ Al ₄₇ ) _100-X Ge _X was weighed to prepare a raw material. (B) By using the raw material and performing plasma arc melting, 14 ingots having a diameter of 50 mm and a length of 15 mm were obtained. In this case, in order to improve the uniformity of each component, the ingot was turned over after the first melting, and the second melting was performed. (C) A diameter of 60 to 70 mm and a length of 11 are obtained by performing arc skull melting using the 14 ingots.
A material of 0 mm and weight of about 1.5 kg was obtained. (D) The material was heat-treated at 1573K for 3 hours to obtain a TiAl-based intermetallic compound.

The metallographic structure of this TiAl-based intermetallic compound is composed of a layered structure L having a volume fraction Vf of 80% or more. Therefore, the characteristics of the layered structure L directly relate to the characteristics of the TiAl-based intermetallic compound. affect.

Next, a round bar-shaped test piece T shown in FIG. 3 was produced from the TiAl intermetallic compound and various tests were conducted. The dimensions of the test piece T are as follows: total length a = 99 mm, length of both grips b =
22mm, length of both large diameter parts c = 4mm, length of both middle diameter parts d =
10 mm, small diameter length e = 25.4 mm, large diameter diameter f
= 9.5 mm, medium-diameter portion diameter g = 6.6 mm, small-diameter portion diameter h = 6.35 mm, both flange portion diameter k = 8.3 mm, and both flange portion thickness m = 2 mm.

FIG. 4 shows the relationship between the average width w ₁ of the TiAl phase p2 and the creep strength. This creep strength is 10
It is expressed as the rupture intensity at 0 hours.

As is apparent from FIG. 4, 0.1 atomic% ≦
It can be seen that when Ge ≦ 0.5 atomic%, the average width w ₂ of the TiAl phase p2 is expanded with an increase in the Ge content, and the creep strength of the TiAl-based intermetallic compound is improved. G
When e> 0.5 atom%, a large amount of precipitates are generated, and thus the creep strength sharply decreases.

FIG. 5 shows the relationship between the Ge content and the average width w ₁ of the TiAl phase p2.

As is apparent from FIG. 5, 0.1 atomic% ≦
It can be seen that the average width w ₁ of the TiAl phase p2 can be controlled when Ge ≦ 0.5 atomic%. However, when Ge> 0.5 at%, a precipitate is generated, so that the expansion of the average width w ₁ stops.

FIG. 6 shows the relationship between the average width w ₁ of the TiAl phase p2 and the average grain size d of the layered structure L.

As is apparent from FIG. 6, 0.1 atomic% ≦
Average width w of TiAl phase p2 in Ge ≦ 0.5 atomic%
It can be seen that although ₁ changes, the average grain size d of the layered structure L hardly changes.

FIG. 7 shows the relationship between the average width w ₁ of the TiAl phase p2 and the room temperature tensile strength. In this test, the creep test specimen T was used.

As is clear from FIG. 7, the TiAl phase p2
It can be seen that the room temperature strength is maintained in a rising tendency despite the expansion of the average width w ₁ of the.

FIG. 8 shows the relationship between the average grain size (corresponding to d) of the lamellar structure and the normal temperature tensile strength in the GeAl-free TiAl intermetallic compound. The control of the average grain size was performed by controlling the cooling rate of passing through the transformation point of α phase → α ₂ phase + γ phase in the heat treatment. From FIG. 8, it can be seen that the room temperature strength decreases as the average grain size of the layered structure increases.

[0027]

According to the present invention, by adopting the unique method as described above, it is possible to obtain a TiAl-based intermetallic compound in which the room temperature strength is kept increasing and the creep strength is improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing a metal structure of a raw material.

FIG. 2 is a schematic view showing a metallographic structure of a TiAl-based intermetallic compound.

FIG. 3 is a front view of a test piece.

FIG. 4 is a graph showing the relationship between the average width of the TiAl phase and creep strength.

FIG. 5 is a graph showing the relationship between the Ge content and the average width of the TiAl phase.

FIG. 6 is a graph showing the relationship between the average width of the TiAl phase and the average grain size of the layered structure.

FIG. 7 is a graph showing the relationship between the average width of the TiAl phase and room temperature tensile strength.

FIG. 8 is a graph showing the relationship between the average grain size of a layered structure and room temperature tensile strength.

[Explanation of symbols]

L lamellar structure p1 Ti ₃ Al phase p2 TiAl phase d average particle diameter w _1, w ₂ average width

Claims (1)

[Claims] 1. A layered structure in which a Ti ₃ Al phase and a TiAl phase are alternately laminated, and a Ge content of 0.1 atomic%.
Producing a material set to ≦ Ge ≦ 0.5 atomic%, and then subjecting the material to heat treatment to laminate a Ti ₃ Al phase and a TiAl phase while suppressing an increase in the average grain size of the layered structure. A method for producing a TiAl-based intermetallic compound having high creep strength, which comprises expanding the average width of the TiAl phase in the direction from the average width of the material.