JPH0525571A - High strength ni-al intermetallic compound - Google Patents

Abstract

PURPOSE:To obtain a structural material for high temp. use good in high strength and cold ductility by adding a specified amt. or below of Re to a B2 type Ni-Al alloy and increasing its strength without deteriorating the ductility shown in the case the atomic ratio of Ni:Al lines in 1:1. CONSTITUTION:This high strength Ni-Al intermetallic compound is obtd. by adding, by atom, 3% Re to a B2 type Ni-Al alloy. The amt. of Re to be added is preferably regulated to 0.5 to 3%, and even in the case of less than 0.5%, the atomic ratio of Ni:Al substantially lines in 1:1, thus, its ductility is not deteriorated, and its strength can be improved by solid-soln. strengthening. When Re is added by >=0.5%, a secondary phase is deposited, so that its crystalline grains can apparently be refined, the deterioration in its ductility can be prevented by the effect of improving ductility and its strength can furthermore be improved. In the case of >3% Re, the deterioration in its ductility is remarkable, its strength also deteriorates as well as the addition of large amounts of Re is made difficult and the specific gravity of intermetallic compounds is made large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength NiAl-based intermetallic compound having excellent oxidation resistance, and more specifically, to high temperature for a long time such as a gas turbine, a jet engine, a high temperature valve, a high temperature gas furnace and the like. It relates to the structural material to be exposed.

[0002]

2. Description of the Related Art The demand for gas turbines with higher thermal efficiency and the demand for faster aircraft have been increasing in recent years. Development of structural materials is in progress. At present, Ni-based superalloys are mainly used because they are excellent in high temperature strength.
Since the number of added elements is extremely large, it is difficult to melt and cast, and there is a problem that the strength is greatly reduced at 700 ° C or higher.

[0003] Therefore, recently conducted many studies on the L1 ₂ type Ni ₃ Al intermetallic compound is a major strengthening phase at a high temperature Ni base superalloys (e.g., JP-55-58
346, JP 56-69342, JP 62-93332 Patent Publication), Ni ₃ Al intermetallic compound with improved room temperature ductility and high temperature strength by the addition of the third element is manufactured. However, the L1 ₂ type Ni ₃ Al-based intermetallic compound can hardly exceed the Ni-based superalloy in terms of strength and oxidation resistance even if the third element is added, and the addition of the third element makes it possible to obtain a specific gravity. However, there are drawbacks such as large size.

On the other hand, B2 type NiA excellent in oxidation resistance
Much research has been done focusing on l-based intermetallic compounds.
[For example KHHahn and K. Vedula: Scripta Metall., 23
(1989), 7.]. However, this B2-type NiAl-based intermetallic compound has a drawback that it exhibits ductility when the atomic ratio of Ni and Al is 1: 1, but its strength is weak, and it does not exhibit ductility at a ratio other than this atomic ratio. Furthermore, there is no report that an additive element that can improve this defect has been found.

[0005]

DISCLOSURE OF THE INVENTION The object of the present invention is B2.
It is an object of the present invention to provide a structural material that is lightweight and has excellent oxidation resistance and that maintains high strength even at high temperatures by adding a third element capable of improving strength while maintaining the ductility of the type NiAl-based intermetallic compound.

[0006]

Means for Solving the Problems The constitution of the present invention for attaining the above-mentioned object is as follows: Ni (Al) alloy represented by B2 type is added with Re (rhenium) in an amount of 3 atomic% or less to obtain a high-strength NiAl-based metal. The main point is to obtain an intermetallic compound.

[0007]

Function: B2-type NiAl intermetallic compound (hereinafter referred to simply as Ni
(Also sometimes referred to as Al), the atomic ratio of Ni: Al is 1:
In the case of 1, ductility is exhibited, and it is known that this ductility increases as the crystal grain size becomes finer (for example, "Intermetallic compound", published by Nikkan Kogyo Shimbun). This is because when the crystal grain size is large, deformation is concentrated in large crystal grains and does not lead to improvement in ductility, but in the case of fine crystal grains, the constraint from adjacent crystal grains is large, As a result, the deformation does not occur only in the crystal grains of the sample, and when the deformation occurs in a part of the grains, the deformation does not concentrate in a part of the sample, and the deformation also occurs in a wide range of adjacent crystal grains. To propagate,
It is considered that this is because the ductility increases as a whole.

By precipitating the second phase in the crystal grains of NiAl, the present inventors have improved the strength due to the precipitation effect and created an interface with the second phase in the crystal grains to refine the crystal grain size. It was thought that it was possible to obtain the same ductility as in the case of the above, and the research was conducted on the effect of additional elements on the B2 type NiAl intermetallic compound. As a result, it was revealed that when Re was added to NiAl, the strength could be significantly improved without impairing the ductility of NiAl having an atomic ratio of 1: 1.

The amount of Re added to the B2 type NiAl-based intermetallic compound in the present invention is preferably 0.5 to 3 atomic%, but even if added in a small amount of less than 0.5 atomic%, the atomic ratio of Ni to Al is reduced. Is substantially 1: 1 so that ductility is not impaired and strength is improved by solid solution strengthening. Although the atomic ratio of Ni and Al should deviate from 1: 1 as the amount of Re added increases, ductility should decrease, but if Re is added in an amount of 0.5 atomic% or more, the second phase will precipitate. Therefore, the crystal grains are apparently made finer, and the ductility can be prevented from lowering due to the effect of improving the ductility as described above. Further, precipitation strengthening improves the strength.

Addition of Re in excess of 3 atomic% to NiAl causes a remarkable decrease in ductility and also a decrease in strength. Further, since Re is an element having a high melting point (3180 ° C.), for example, the melting method, etc. Is difficult to add in large quantities,
In addition, it is not preferable because it causes segregation and further deviates from the object of the present invention to provide a lightweight structural material because of its large specific gravity.

[0011]

EFFECTS OF THE INVENTION According to the present invention, the strength can be significantly increased while the room temperature ductility of the B2 type NiAl intermetallic compound is ensured, and a structural material for high temperature having excellent oxidation resistance can be provided. Became.

[0012]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. Example B A 1 kg ingot (see Table 1) in which various additive elements were mixed with a 2 type NiAl alloy was melted by a non-consumable tungsten arc melting method, and homogenized at 1200 ° C. for 24 hours, and then 3 mm × A 4 mm × 40 mm bending test piece was sampled, a 3-point bending test was performed at a crosshead speed of 0.5 mm / min, and the bending strength, the amount of flexure, and the fracture mode were determined from the crosshead displacement-load curve. did.

[0013]

[Table 1]

As is clear from Table 1, Examples 1 to 3 are
The amount of deflection was the same as that of Comparative Example 4 in which Re was not added, and since the plastic region was destroyed, Ni: Al was 1: 1.
It can be seen that the ductility in the case of is not impaired. On the other hand, the bending strength is greatly increased as compared with Comparative Example 4. However, when Re is added in an amount of 5 atomic% or more, the amount of deflection is reduced. Furthermore, elements other than Re, Ir, Co, Fe, Mn
However, even if added, no one showing a large ductility at the level of the example was obtained.

Claims (1)

Claim: What is claimed is: 1. A high-strength NiAl-based intermetallic compound obtained by adding Re in an amount of 3 atomic% or less to a NiAl alloy represented by B2 type.