JPS61270353A - Sintered compact of ni3al intermetallic compound and its production - Google Patents

Abstract

PURPOSE:To manufacture a sintered compact of Ni3Al intermetallic compound excelling in strength at high temp. and having high density by mixing powdered high-purity Al and powdered Ni in a specific ratio, compacting the mixture by a hot pressing process and sintering the green compact in a nonoxidizing atmosphere. CONSTITUTION:The powdered Al of extremely high purity is mixed with the Ni powder in the ratio of Al to Ni of 6-20% to 94-80% and the powder mixture is put into a die made of graphite and is subjected to hot press compacting at 500-700 deg.C for 15min-5hr at a pressure of 50-500kg/cm<2>. Then the resulting green compact is sintered at 1,000-1,300 deg.C in the atmosphere of reducing gas such as H2 or in vacuum, so that the sintered compact of <=2% total porosity having an isotropic crystal structure, consisting of Ni3Al intermetallic compound with <=5mu fine crystals, having high density and excelling in strength at high temp. can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an excellent Ni3Al intermetallic compound sintered body that is considered to be used as a heat-resistant structural material, and a method for manufacturing the same using a powder metallurgy method.

[Conventional technology]

In recent years, attention has been focused on the excellent high-temperature properties of intermetallic compounds, and attempts have been made to use these compounds as heat-resistant structural materials for turbine components, high-temperature spring materials, engine components, or corrosion-resistant materials. Among these, Ni and Am intermetallic compounds are one of the compounds that have attracted particular attention because they have the unique property of increasing their strength at high temperatures.

Conventionally, the method for producing Ni3Al intermetallic compounds has been the casting method (which has become the mainstream in British patents) in order to avoid the problems of difficult-to-work and difficult-to-cut properties peculiar to intermetallic compounds.However, in the casting method, Ni Problems include problems such as segregation due to the large difference in specific gravity between Al and Al, resulting in non-uniform alloying, and excessive Ni content in the resulting compound due to selective evaporation of Al, a low melting point component, during melting. There was a point.

In addition, from the viewpoint of manufacturing costs, the melting furnace requires excessive energy and is often expensive.

As a method to overcome these drawbacks, a method for producing a Ni5Al intermetallic compound using a powder metallurgy method that can mold a molded product close to the final product shape is disclosed in US Pat. No. 3,486,833, and a similar method for producing a 111Al intermetallic compound is specially disclosed. Kaisho 52-92
No. 808, US Pat. No. 3,715,791.

[Problems to be Solved by the Invention] However, in the powder metallurgical production method of Ni3A'l all 3A' compounds that has been reported so far, the sintered density is low and the sintered body usually has a density of several coefficients to several tens of times. Because it has pores,
It has poor strength and toughness, making it difficult to apply it to heat-resistant structural materials.

U.S. patent for method of obtaining high-density material by powder metallurgy
If the rolling method described in the specification of No. 3,715,791 is adopted, the porosity can be reduced to about 3%, but since the structure is unidirectional, the strength becomes anisotropic, which is not preferable.

The object of the invention is to overcome the aforementioned drawbacks of the prior art.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and has an isotropic crystal structure consisting essentially of microcrystals of Ni3Al with a size of 5μ or less. and has a porosity (true porosity including open pores and closed pores, referred to as total porosity) of 2 or less, particularly 1 or less. In addition, an Al and Ni-containing mixed powder with an Al content of 6 to 20% Ni by weight is hot pressed at 500 to 700C, and then the hot pressed powder is heated in a reducing oven or in a vacuum furnace. The present invention provides a method for producing a Ni5A'l intermetallic compound having high density and isotropic strength by firing at 1000 to 300°C.

Although the present invention provides such an excellent sintered body, the method for producing the same will be mainly explained below.

The raw material powder used in the present invention, such as Al powder, Ni powder, and Al-Ni alloy powder, is 10 pm or less, especially several μm or less, specifically 5 pm or less, prepared by carbonyl method or gas atomization method. The following are preferable, and in particular, as the Al powder, inert gas atomized powder with a small amount of oxidation is particularly preferable. Further, the combination of Ni5A/1 synthetic raw material powder may be any combination, but is preferably Al-
It has been found that Ni alloy powder and Ni powder and Al powder and Ni powder can be used, and Al powder and Ni powder are particularly excellent as raw materials from which a high-density body can be obtained. In any case, the purity of Ni and Al as these powders is preferably high, and it is usually desirable to use 99.9% or more, particularly 9999% or more.

The composition ratio of Al and Ni is 6 to 20% by weight of Al, and the balance is N.
A range of i is preferable, and a range of 12 to 15% by weight of Al produced by 100% Ni3Al and balance Ni is preferable for I#. When the weight percent of Al is in the range of 6 to 12, Ni
When Ni3Al and Ni3Al coexist and the Al weight pot is in the range of 15 to 20! JiAl and Ni5Al will coexist, but in both cases the composition ratio of Ni and Al is high,
The method of the present invention exhibits high properties similar to those of 100% Ni5Al products.

As suitable manufacturing conditions in the present invention, the hot press temperature is preferably in the range of 500 to 700°C.
This is particularly preferred since the fluidity of Al can be utilized most within the QC range and a high density body can be obtained. At temperatures below 500°C, only porous materials with a porosity of 1° or more can be produced;
At temperatures above 0°C, Al evaporation occurs, which is undesirable. Here, the hot pressing pressure is usually about 50 to 500.9/2, preferably about 100 to 350 to 732, and the time is preferably about 15 minutes to 5 hours, preferably about 30 to 3 hours. Moreover, since it is a mere composite of Ni and Al after hot pressing, it has the characteristic that it can be deformed by cutting or forging.

The highest density can be achieved at a firing temperature of 1000 to 1300°C, particularly preferably 1200 to 1250°C. At temperatures above 1,300°C, densification further progresses, but this is not desirable as the crystal structure becomes coarser and the strength decreases as the recrystallization temperature is exceeded, and below 1,000°C, diffusion does not proceed, making it difficult to form Ni3A'l. ,
This is not preferable because a high-density body cannot be obtained.

In addition, the firing atmosphere after hot pressing may be anything other than an oxidizing atmosphere, but in a neutral atmosphere such as an N2 atmosphere, some N2 and Am may react and form AIN.
Since this acts as an obstacle layer that inhibits the diffusion reaction between Ni and Mu1, it is preferably reduced or under vacuum.

To specifically explain the manufacturing procedure in the present invention, 1413
Mu1 Mechanical stirring of the synthetic raw material mixed powder, which is the usual mixing method,
After processing by ball mill mixing and attritor mixing,
The mixed powder was placed in a graphite mold and hot pressed in a reducing atmosphere (for example, at a pressure of 100 to 350 Yu/cm and a temperature of 500 to 700° C. for 2 hours). At this stage, a mixed molded body of Ni and Al with a total porosity of 2 cm or less was obtained.

Next, this molded body is heated to 100% in a reducing or vacuum atmosphere.
IJis
An Al intermetallic compound was created.

The compound sintered body obtained in this way is a high-density body with a total porosity of 2 cm or less, especially 1% or less, and has an isotropic microcrystalline structure. The structure can be substantially composed of Ni5Al intermetallic compound crystals with a size of 5μ or less, especially 3゛μ or less. These materials have high strength and toughness enough to be used as heat-resistant structural materials.

[For production]

In the production of Ni3Al intermetallic compounds using powder metallurgy, which has traditionally been difficult to obtain high-density and high-strength bodies, the fluidity of Al can be maximized by appropriately selecting production conditions such as hot pressing temperature. By appropriately selecting the firing temperature just below the recrystallization temperature, it was possible to obtain Ni3Al having an isotropic microcrystalline structure and exhibiting high strength properties.

The sintered compound according to the present invention can also be ground again and used as a powder raw material.

〔Example〕

Example 1 Carbonyl Ni powder with a particle size of 2 to 3 μm, Ar gas atomized powder with a particle size of 5 μm or less, Ni: Al=87:
The mixture was blended at a ratio of 131i%, mixed in a ball mill for 6 minutes in ethanol, and then dried.

Next, a mixture of IJi powder and Al powder was placed in a graphite mold and Ar −
350 kll/cm2 pressure in 10% H2 flow 660
Hot press molding was carried out at ℃ for 2 hrs. This molded body was fired in vacuum at 1250° C. for 5 hrs to produce a Ni3A'l intermetallic compound. Ni, A obtained in this way
I is the total porosity [1L 9%, and most of the crystal grain sizes are isotropic, with a diameter of 5 μm or less. And the physical properties are strength 100
kl? /m" (room temperature), 50yu7w" (800℃)
The fracture toughness was 48 MMm (at room temperature).

Examples 2 and 6 The results of sintered bodies obtained in substantially the same manner as in Example 1 except for the ratio of Al and Ni were as follows.

The crystal structure was almost the same as in Example 1.

For comparison, values obtained by the method described in U.S. Pat. No. 3,715,791, which is a powder metallurgy method similar to the method of the present invention but with different manufacturing conditions, and U.S. Pat. No. 5,955,642 obtained by a casting method different from the method of the present invention. The stated values were cited as Reference Examples 1 and 2, respectively.

[Effects of the Invention] Compared to conventionally reported cast materials and powder metallurgy materials, the Ni3A'l sintered body obtained by the present invention has the following advantages:
It has not only sufficient fracture toughness but also high strength properties, and it is possible to perform molding processes that were conventionally difficult after hot press molding, and its industrial value is extremely large. It is something.

Claims (12)

[Claims] (1) Al: 6-20%, Ni: 94-80% by weight
A high-density Ni_3Al intermetallic compound sintered body having an isotropic crystal structure consisting essentially of microcrystals of Ni_3Al of 5 μm or less and having a total porosity of 2% or less. (2) The sintered body according to claim 1, comprising 12 to 15% Al and 88 to 85% Ni. (3) The sintered body according to claim 1 or 2, which has a total porosity of 1% or less. (4) The content ratio of Al and Ni is 6 to 20% by weight, the former being 6 to 20% by weight.
%, the latter of which is 94 to 80%, is hot pressed at 500 to 700°C, and then fired at 1000 to 1300°C in a non-oxidizing atmosphere. A method for producing an intermixture sintered body. (5) The method according to claim 4, wherein the powder to be hot pressed has a diameter of 5 μm or less. (6) The method according to claim 4, wherein the content ratio of Al and Ni is 12 to 15% for the former and 88 to 85% for the latter. (7) The method according to claim 4, wherein the non-oxidizing atmosphere is reducing or vacuum. (8) The powder containing Ni and Al components is Al powder or Al-
The method according to claim 4, which is a mixed powder of Ni alloy powder and Ni powder. (9) The method according to claim 8, wherein the powder containing Ni and Al components is a mixed powder consisting of Ni powder and Al powder. (10) The method according to claim 4, wherein the powder containing Ni and Al components is a high purity powder with a purity of 99.9% or more of Ni and Al components. (11) The method according to any one of claims 4 to 10, wherein the hot press temperature is 640 to 660°C. (12) Firing temperature after hot pressing is 1200-125
The method according to claim 4 or 11, wherein the temperature is 0°C.