JPH0551681A - High strength tial intermetallic compound - Google Patents

Abstract

PURPOSE:To improve strength by incorporating a TiAl intermetallic compound composition containing specific proportion of Al and specific amounts of oxygen and constituting a metallic structure of TiAl phases and Ti3Al phases of specific volume fraction. CONSTITUTION:This TiAl intermetallic compound contains a TiAl intermetallic compound composition consisting of 36-60 atomic % Al and the balance Ti and 0.01-1wt.% oxygen and has a metallic structure which is composed of a dual-phase structure of TiAl phases (gamma) and Ti3Al phases alpha2 and where the volume fraction Vf of the phases alpha2 is set at 1-80% and this intermetallic compound has high strength. As to oxygen content, the strength improving effect is decreased when it is below the lower limit, and, when it exceeds the upper limit, the amount of oxygen in the form of solid solution in the phases (gamma) is increased and the ductility of the above intermetallic compound at ordinary temp. is deteriorated. Further, when the volume fraction Vf of the phases alpha2 is below the lower limit, the effects of improving strength and ductility at ordinary temp. are decreased because oxygen is not preferentially allowed to enter into solid solution, and, on the other hand, when it exceeds the upper limit the characteristics of the phases (gamma), that is, light weight and high specific strength are deteriorated and the ductility of the above intermetallic compound at orfinary temp. is deteriorated.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a high-strength TiAl-based intermetallic compound.

[0002]

2. Description of the Related Art TiAl-based intermetallic compounds have been attracting attention as structural materials for engine parts and the like because they are lightweight and have excellent heat resistance.

[0003]

However, the conventional TiAl-based intermetallic compound has a problem that it is poor in practicability because of its low strength.

In view of the above, the present invention improves the metal structure and contains oxygen as the third element to improve the strength of TiAl without impairing the room temperature ductility.
An object is to provide a system-based intermetallic compound.

[0005]

High strength Ti according to the present invention
The Al-based intermetallic compound contains 36 atomic% or more and 60 atomic% or less of Al and the balance is TiAl-based intermetallic compound composition, and 0.01 wt% or more and 1 wt% or less of oxygen. Containing a TiAl phase γ and Ti
_{It is characterized} by having a two-phase structure having a ₃ Al phase α ₂ and having a volume fraction Vf of the Ti ₃ Al phase α ₂ set to 1% or more and 80% or less.

[0006]

EXAMPLE FIG. 1 schematically shows an example of the metallographic structure of a TiAl-based intermetallic compound.
It has a two-phase structure having an Al phase γ and a Ti ₃ Al phase α ₂ , in the illustrated example, an aggregate of layered structure parts (lamella structure parts) L in which both phases γ and α ₂ are alternately deposited. In order to obtain such a metal structure, the Al content is 36 atomic% in terms of composition.
As described above, it is necessary to set it to 52 atomic% or less.

In this case, the volume fraction V of the Ti ₃ Al phase α ₂ is
f is 1% or more and 80% or less, preferably 5% or more, 60
By setting it to be not more than%, the room temperature ductility of the TiAl-based intermetallic compound can be improved. From the viewpoint of improving the room temperature ductility, the average grain size of the layered structure portion L is 1 μm or more,
It is preferably 1000 μm or less.

FIG. 2 schematically shows another example of the metal structure of the TiAl-based intermetallic compound. This metal structure is T
It is composed of a single phase portion Sγ consisting of only the iAl phase and a layered structure portion L in which TiAl phase γ and Ti ₃ Al phase α ₂ are alternately deposited and dispersed in the single phase portion Sγ. In order to obtain such a metallographic structure, it is necessary to set the Al content to 45 atom or more and 60 atom% or less in terms of composition.

In this case, the room temperature ductility of the TiAl intermetallic compound can be improved by setting the volume fraction Vf of the layered structure L to 15% or more, preferably 35% or more. From the viewpoint of improving room temperature ductility, the average grain size of the layered structure portion L is preferably 1 μm or more and 1000 μm or less.

According to the present invention, T containing 36 atomic% or more and 60 atomic% or less of Al that develops the metal structure as described above is contained.
0.01 wt% or more in the iAl-based intermetallic compound composition,
An oxygen-containing TiAl-based intermetallic compound is formed by containing 1% by weight or less of oxygen.

As described above, the TiAl-based intermetallic compound is
TiAl phase γ and Ti₃Al phase α ₂With the acid
Element is Ti as an interstitial element₃Al phase α₂Preferentially to
It has the function of melting, and by this function Ti₃Al phase α₂
Is solid-solution strengthened, so the high strength of TiAl-based intermetallic compounds
Degree is achieved. On the other hand, oxygen forms a solid solution in the TiAl phase γ.
Then, the TiAl phase γ is embrittled, and the TiAl-based metal is
Although the room temperature ductility of the intermetallic compound is impaired, as described above, Ti₃
Al phase α₂By preferential solid solution of oxygen to TiAl-based gold
Normal temperature ductility due to the two-phase structure of the intergeneric compound is maintained.

However, the oxygen content is 0.01% by weight.
If less than 1%, the strength improving effect is small, while if over 1% by weight, the solid solution amount of oxygen in the TiAl phase γ is increased and TiAl
The room temperature ductility of the intermetallic compound decreases. Also Ti ₃ Al
If the volume fraction Vf of the phase α ₂ is less than 1%, preferential solid solution of oxygen is not carried out, so the strength and room temperature ductility improving effect is small, while if it exceeds 80%, the TiAl phase γ is lightweight and Properties such as high specific strength are impaired, and TiAl
The room temperature ductility of the intermetallic compound decreases.

The oxygen-containing intermetallic compound was produced by the following method.

First, Ti (sponge titanium) having a purity of 99.5% and Al (aluminum shot) having a purity of 99.99% were weighed to a target composition in the range of 45 atomic% ≦ Al ≦ 52 atomic%, Then, this weighed material was melted under Ar atmosphere using a non-consumable arc melting furnace while adding TiO ₂ as an oxygen source to the material at an appropriate time to obtain an ingot. Then in the ingot, 1000-1400
Heat treatment was performed at a temperature of 10 minutes to 24 hours to obtain an oxygen-containing TiAl-based intermetallic compound. In this case, Ti
₃ The volume fraction Vf of the Al phase α ₂ was adjusted by changing the amount of Al, the heat treatment temperature and the heat treatment time.

Next, the volume fraction Vf of the Ti ₃ Al phase α ₂ and the oxygen content in the oxygen-containing TiAl intermetallic compound were measured.

The volume fraction Vf of the Ti ₃ Al phase α ₂ was measured by polishing a test piece prepared from the above compound to a mirror surface and then obtaining a composition image photograph by a scanning electron microscope (SEM). It was performed using an image analyzer based on the photograph. The oxygen content was measured by counting the characteristic X-rays of oxygen by point analysis (analysis area of 1 μm) using an electron probe microanalyzer (EPMA). As a result, the Ti ₃ Al phase α ₂ and the TiAl phase γ
It was confirmed that the ratio of the oxygen content in ( ₂₎ was approximately α ₂ : γ = 3: 1.

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

From the above intermetallic compound, 3 mm long, 4 mm wide,
A test piece having a length of 37 mm was manufactured, and the test piece was subjected to a 4-point bending test (JIS R 1601) at room temperature.
In this test, the crosshead speed was set to 0.5 mm / min, the strain and the rolling load due to the strain gauge attached to the extension side of the test piece were measured, and the true strain amount and proof stress were determined from these measured values. I asked.

FIG. 3 shows the relationship between the oxygen content and the yield strength and true strain amount in the bending test. In the figure, the line a corresponds to the proof stress, and the line b corresponds to the true strain amount. The composition of each test piece is (Ti ₅₃ Al ₄₇ ) _100-x (O ₂ ) in atomic%.
Represented by _X, Ti ₃ Al phase alpha ₂ volume fraction Vf is 20
%. As is clear from FIG. 3, the oxygen content is less than 0.
By setting the content to be not less than 01% by weight and not more than 1% by weight, the proof stress of the oxygen-containing TiAl-based intermetallic compound, that is, the strength can be improved, and the true strain amount, that is, the room temperature ductility can be improved.

FIG. 4 shows the relationship between the oxygen content and the true strain amount by the bending test. The composition of each test piece is atomic%
And is represented by (Ti ₅₃ Al ₄₇ ) _100-x (O ₂ ) _X.
In the figure, each line c to h and the volume fraction Vf of the Ti ₃ Al phase α ₂
The relationship with is as shown in Table 1.

[0021]

[Table 1] As is clear from FIG. 4 and lines d to g, the oxygen content is 0.
It is set to 01% by weight or more and 1% by weight or less, and Ti ₃ A
By setting the volume fraction Vf of the l-phase α ₂ to 1% or more and 80% or less, the true strain amount of the oxygen-containing TiAl-based intermetallic compound, and thus the room temperature ductility, can be improved.

The two-phase structure in the present invention includes a case where the two-phase structure is composed of a lamellar structure and an equiaxed crystal of Ti ₃ Al phase α ₂ .

[0023]

According to the present invention, a TiAl intermetallic compound having excellent strength and room temperature ductility can be provided by specifying the amount of Al, the amount of oxygen and the metal structure as described above.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a metal structure.

FIG. 2 is an explanatory diagram showing another example of the metal structure.

FIG. 3 is a graph showing the relationship between the oxygen content and the yield strength and true strain amount in the bending test.

FIG. 4 is a graph showing the relationship between the oxygen content and the true strain amount by a bending test.

[Explanation of symbols]

α ₂ Ti ₃ Al phase γ TiAl phase L Layered structure

Claims (1)

[Claims] 1. Al of 36 atomic% or more and 60 atomic% or less
Containing a TiAl-based intermetallic compound composition with the balance being Ti, and 0.01 wt% or more and 1 wt% or less oxygen, and the metallographic structure of the TiAl phase γ and the Ti ₃ Al phase α ₂ A high-strength TiAl-based intermetallic compound, characterized in that the volume fraction Vf of the Ti ₃ Al phase α ₂ is set to 1% or more and 80% or less.