JPH0551680A - Tial intermetallic compound having high strength, high toughness, and high ductility - Google Patents

Abstract

PURPOSE:To improve strength, toughness, and ductility by specifying the average crystalline grain size and the amount of contained oxygen in a TiAl intermetallic compound, respectively. CONSTITUTION:This TiAl intermetallic compound has a composition consisting of 36-60 atomic % Al and the balance Ti and also has <=50mu average crystalline grain size and <=1.0wt.% contained oxygen content. When the average grain size exceeds 50mu, the regularity of crystal orientation is increased and, as a results, transgranular cleavage is allowed to occur and the strength, toughness, and ductility of the above intermetallic compound are deteriorated. Further, when the amount of contained oxygen exceeds 1.0wt.%, the toughness and ductility of the above intermetallic compound are deteriorated similarly. Because this intermetallic compound is obtained by regulating the amount of oxygen contained in powdery raw materials at the time of preparing these powdery raw materials and also regulating the crystalline grain size by means of heat treatment, the refining of crystalline grains and the reduction in the amount of contained oxygen can be relatively easily attained.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to high strength and high ductility TiAl.
Related to intermetallic compounds.

[0002]

2. Description of the Related Art TiAl-based intermetallic compounds are noted as a structural material for engine parts and the like because they are lightweight and have excellent heat resistance.

[0003]

However, in general, TiAl-based intermetallic compounds are poor in workability due to low room temperature ductility, and are poor in practicability due to low strength and toughness even when commercialized. There's a problem.

Therefore, at present, it is attempted to improve the mechanical properties of the TiAl-based intermetallic compound by adding a third element such as Mn. In this case, long-term homogenization heat treatment is performed. Since implementation is indispensable, new problems will occur in terms of production, such as increased production costs and reduced production efficiency.

In view of the above, the present invention separates from the technical point of view of the addition of the third element, and adjusts the crystal grain size and the oxygen content to improve the strength and toughness and ductility of the TiAl intermetallic compound. The purpose is to provide.

[0006]

The high-strength and high-toughness ductile TiAl-based intermetallic compound according to the present invention has an average crystal grain size of 50 μm.
m or less, and the content of oxygen is 1.0 wt% or less.

[0007]

EXAMPLES In the TiAl-based intermetallic compound according to the present invention, the composition is 36 atomic% or more and 60 atomic% or less of A.
1 and the balance Ti, and the average crystal grain size is 50 μm.
And the oxygen content is 1.0 wt% or less.

When the Al content is set as described above, the crystal grains are refined to randomize the crystal orientation, and the oxygen content that causes embrittlement is further reduced, the fracture mode of the TiAl-based intermetallic compound is reduced. It is possible to improve the strength and toughness and ductility of the TiAl-based metal compound by shifting the grain boundary from intragranular cleavage to grain boundary fracture.

In order to reduce the crystal grain size, generally, a fine raw material powder is used. However, the finer the raw material powder, the larger the amount of oxygen contained therein. As expected, therefore Ti
The strength and toughness and ductility of the Al-based intermetallic compound cannot be improved.

In the present invention, the amount of oxygen contained in the powder is adjusted during production of the raw material powder, and the crystal grain size is adjusted by heat treatment. Can be easily achieved.

However, if the Al content is less than 36 atomic%, the toughness and ductility of the TiAl intermetallic compound is low, while if it exceeds 60 atomic%, the strength of the TiAl intermetallic compound decreases. Further, when the average crystal grain size exceeds 50 μm, the regularity of the crystal orientation is strengthened, so that intra-grain cleavage occurs and TiA
The strength and toughness and ductility of the l-based intermetallic compound decrease. If the oxygen content exceeds 1.0 wt%, TiA
The toughness and ductility of the l-based intermetallic compound decreases.

Next, specific examples of the TiAl intermetallic compound will be described.

First, a TiAl intermetallic compound was manufactured by the following method.

Ti (sponge titanium) with a purity of 99.5%
And 99.99% purity Al (aluminum shot) were weighed so that the Al content was 48 atomic%, and the weighed product was melted using a plasma melting furnace to obtain an ingot. Use that ingot as an electrode,
Under the application of the PREP method (plasma rotating electrode method), a rapidly solidified powder having an average particle diameter of 200 to 250 μm and an oxygen content of 0.03 to 0.5% by weight was produced.

The rapidly solidified powder was placed in a Ti can body, subjected to vacuum degassing treatment, and then the can body was sealed. Next, the powder-encapsulated can body was subjected to HIP treatment (hot isostatic pressing treatment) under the conditions of 1200 ° C., 147 MPa, and 3 hours to obtain various raw materials of 48 atomic% Al made of a sintered body.

The rapidly solidified powder is subjected to a mechanical forced straining treatment using a high energy ball mill to obtain an average particle size of 25 to 50 μm and an oxygen content of 0.5 to 2.0% by weight.
Processed powder was produced. Then, the treated powder was subjected to HIP treatment under the same conditions as described above to obtain various raw materials of 48 atomic% Al made of a sintered body.

After that, 1000 to 1300 ° C. for each material,
Heat treatment was performed for 1 to 72 hours to obtain various TiAl-based intermetallic compounds having an adjusted average crystal grain size and oxygen content.

In order to examine the strength and toughness and ductility of the TiAl intermetallic compound, the following room temperature bending test was conducted.

From the above-mentioned intermetallic compound, length 3 mm, width 4 mm,
A test piece having a length of 37 mm was manufactured, and a 4-point bending test (JIS R 1601) was performed on the test piece. In this test, set the crosshead speed to 0.5 mm / min,
The strain and the rolling load by the strain gauge attached to the stretch side of the test piece were measured, and the bending strength, the bending elongation, and the true strain amount were obtained from the measured values.

FIG. 1 shows the relationship between the average crystal grain size and bending elongation, and FIG. 2 shows the relationship between the average crystal grain size and bending strength. In this case, the oxygen content of each TiAl-based intermetallic compound is 0.5% by weight.

As is clear from FIGS. 1 and 2, the strength and toughness and ductility of the TiAl-based intermetallic compound are improved by setting the average crystal grain size to 50 μm or less when the oxygen content is 0.5% by weight. be able to.

FIG. 3 shows the relationship between the oxygen content and the bending elongation. In this case, the average crystal grain size of each TiAl-based intermetallic compound is 50 μm.

As is apparent from FIG. 3, the average crystal grain size is 5
When the content of oxygen is 0 μm or less, the bending elongation of the TiAl-based intermetallic compound can be improved by setting the oxygen content to 1.0% by weight or less.

FIG. 4 shows the relationship between the oxygen content and the true strain amount due to bending. In the figure, lines a and b correspond to the present invention,
The line a shows the case where the average crystal grain size is 7 μm, and the line b shows the case where the average crystal grain size is 50 μm. Line c corresponds to the comparative example, and the average crystal grain size is 200 μm.

In the present invention shown by both lines a and b, when the oxygen content is decreased and the value becomes 1.0% by weight or less, the strength of the TiAl-based intermetallic compound decreases with the decrease of the oxygen content. It can be seen that the toughness and ductility are gradually improved.

From both lines a and b, when the oxygen content is 1.0 wt% or less and the oxygen content is the same, the TiAl-based intermetallic compound having a smaller average crystal grain size has a smaller average crystal grain size. It can be seen that it has higher strength and higher toughness and ductility than the larger one.

Further, the comparative example of the line c has low strength and low ductility due to the extremely large average crystal grain size even if the oxygen content is small.

[0028]

According to the present invention, by specifying the average crystal grain size and the oxygen content as described above, the TiAl-based metal having excellent strength and ductility without adding the third element. Intermetallic compounds can be provided.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the average crystal grain size and bending elongation.

FIG. 2 is a graph showing the relationship between the average crystal grain size and bending strength.

FIG. 3 is a graph showing the relationship between the oxygen content and bending elongation.

FIG. 4 is a graph showing the relationship between the amount of oxygen contained and the amount of true strain due to bending.

Claims (1)

[Claims] 1. A high-strength and high-toughness TiAl-based intermetallic compound having an average crystal grain size of 50 μm or less and an oxygen content of 1.0% by weight or less.