JPH05295501A - Method for controlling structure of nb-al-base intermetallic compound - Google Patents

Abstract

PURPOSE:To control the structure of an Nb-Al-base intermetallic compound hitherto brittle and difficult to work. CONSTITUTION:This method is a method for controlling the structure of an Nb-Al-base intermetallic compound, where the Nb-Al-base intermetallic compound containing 13-25atomic % Al is hot-worked in vacuum or in an inert gas atmosphere at 1200-1600 deg.C and subjected to recrystallization. Forging is done as hot working. In the structure-controlled Nb-Al-base intermetallic compound, the dendrite as a cast structure is formed into recrystallized fine crystalline grains by hot working, and toughness at room temp. can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a promising Nb-Al based intermetallic compound as an ultrahigh temperature heat resistant material, and is applied to a combustor of an aircraft engine, a turbine and the like as a high temperature heat resistant material.

[0002]

2. Description of the Related Art In recent years, expectations for ultra-high temperature heat resistant materials have been increasing with the increase in output and performance of engines. Research on high-melting-point intermetallic compounds, which have the potential as a heat-resistant structural material, is also being actively conducted (for example, JOM, No. 9, (1989) P12). Nb-
It is known that Nb ₃ Al, Nb ₂ Al and Al ₃ Nb exist as Al-based intermetallic compounds, but their phase diagrams have not been sufficiently prepared and their characteristics have not been clarified. On the other hand, Nb ₃ Al is known as a superconducting material, and a manufacturing method for forming a wire has been disclosed. However, no research and development aimed at using the Nb ₃ Al intermetallic compound as a structural material was made. The reason is that the Nb ₃ Al intermetallic compound is very brittle at room temperature and the oxidation resistance at high temperature is not sufficient. However, since the Nb-Al-based material has a relatively low density and a high melting point, it may be used as a high temperature structural material. N
It has been reported that a b-Al intermetallic compound was produced by a powder method and the mechanical properties thereof were studied. In the report, the relationship between high temperature strength and temperature is shown (Proc.I.
nt. Sypo. on Intermetallic
Compounds (JIMIS-6) 1991 P6
33). Ordinary metals or alloys are subjected to thermomechanical treatment to control their structure. However, since the intermetallic compound is generally difficult to process, the processing method and processing conditions are limited, and it has been difficult to control the structure by the conventional method.

[0003]

DISCLOSURE OF THE INVENTION The present invention is based on Nb ₃ Al, which is mainly Nb ₃ Al, which has been brittle and difficult to process.
An object of the present invention is to provide a method for controlling the microstructure of a base intermetallic compound, improving the structure, and easily producing an intermetallic compound having excellent properties such as brittleness at room temperature, oxidation resistance, and high temperature strength. It is a thing.

[0004]

According to the present invention, an Nb-Al-based intermetallic compound containing 13% or more and 25% or less of Al in atomic% is used at 1200 ° C or higher in a vacuum or an inert gas atmosphere.
It is a method for controlling the structure of an Nb-Al-based intermetallic compound, which is characterized by performing hot working within a temperature range of 00 ° C or less and performing work recrystallization. It is desirable to apply forging as the hot working. 13% or more of Al in atomic% 2
Nb-Al based intermetallic compound containing 5% or less is melted,
By performing hot working at a temperature of 00 ° C. or more and 1600 ° C. or less, the Nb—Al intermetallic compound can be worked and recrystallized to uniformly refine the structure. Examples of hot working methods include forging, hot extrusion, and hot rolling. Among them, forging, particularly isothermal forging, is suitable. The isothermal forging can reduce the strain rate to about 1 × 10 ⁻⁴ / s, and enables processing of difficult-to-process materials. In other hot working,
It is preferable that the deformation speed be slow.

The Nb-Al-based intermetallic compound is melted by plasma arc melting, high frequency induction melting, or the like to dissolve a desired component into an ingot. Internal defects such as cracks increase in the ingot as the amount of Al increases. The ingot undergoes a homogenizing heat treatment at a temperature at which sufficient diffusion occurs. Instead of the homogenizing heat treatment, HIP may be used to eliminate internal defects and simultaneously homogenize the structure. Adjust the ingot to a size suitable for hot working, and place it in a vacuum or in an inert gas atmosphere.
Hot working is performed at a temperature of 00 ° C or more and 1600 ° C or less.
In this case, it is preferable to reduce the strain rate during processing so that uniform deformation occurs. Further, for the purpose of preventing the reaction between the sample and the mold and improving the lubrication between the sample and the metal, it is desirable to sandwich a foil such as Ta between the sample and the mold. It is desirable to apply a compressive component to the deformation, and isothermal forging is suitable as hot working.

[0006]

Function: Nb alloy containing 13% or more of Al in atomic% is N
It has a two-layer structure of b ₃ Al and Nb solid solution and is very brittle at room temperature. When the amount of Al is less than 13%, the volume ratio of Nb ₃ Al decreases, the property of the Nb solid solution becomes dominant, the brittleness at room temperature is improved, and conventional hot working can be used. Further, when the amount of Al exceeds 25%, Nb ₂ Al, which is more brittle than Nb ₃ Al, precipitates and becomes a brittle compound even at high temperatures. Therefore, the Nb-Al-based intermetallic compound targeted in the present invention has an Al content of 13% or more and 25% or less.

The hot working atmosphere needs to be performed in vacuum or in an atmosphere of an inert gas such as Ar or He because the Nb-Al group intermetallic compound undergoes rapid oxidation at a temperature of 800 ° C. or higher. is there. N subjected to homogenization heat treatment
Since the b-Al-based intermetallic compound precipitates Nb ₃ Al from the liquid and the Nb solid solution by a peritectic reaction, it causes a dendrite form. By hot working this structure, the dendrites are destroyed by deformation, processed and recrystallized, and a structure in which Nb solid solution is finely precipitated in the Nb ₃ Al matrix phase is formed. If the hot working temperature is less than 1200 ° C, 10
Since the fracture occurs at a strain amount of less than%, the strain that causes the change in the structure is not accumulated. Further, when the deformation is performed at a temperature higher than 1600 ° C., the deformation proceeds, but at the same time, recrystallization occurs,
As the crystal grains coarsen, the precipitated Nb solid solution becomes
Aggregation causes coarsening. Nb ₃ Al with coarse crystal grains
The brittleness is not improved. Therefore, the processing temperature is 1
The range is 200 ° C. or higher and 1600 ° C. or lower.

[0008]

EXAMPLE The following components were melted by plasma arc melting. The melted ingot is 1600 ℃,
The homogenization heat treatment was performed for 24 hours. For the hot working, forging was performed. A cylindrical test piece (5φ × 7 mm) to which a thermocouple was spot-welded was heated by electric heating in a vacuum atmosphere, and was compressed and deformed by a tungsten carbide jig. The initial strain rate was 5 × 10 ⁻⁴ / s. The relationship between the deformation stress and the deformation temperature at the time of hot working of the Nb-19.4 at% Al sample is shown (FIG. 1). When deformed at 1150 ° C, a brittle fracture occurred during the deformation.
Deformation is possible at 00 ℃, especially 1400 ℃, 160
At 0 ° C, deformation of 20% or more was possible. 1
The microstructure change after deformation was observed for the sample deformed at 400 ° C and 1600 ° C.

FIG. 2 (a) shows the structure before Nb-19.4 at% Al deformation, (b) shows the structure after 1400 ° C. and 20% deformation, and (c) shows the structure after 1600 ° C. and 20% deformation. Figure 2
(A) Microstructure of Nb-19.4 at% Al after heat treatment at 1600 ° C, (b) Microstructure of Nb ₃ Al solid phase finely dispersed in Nb ₃ Al matrix phase by recrystallization at 1400 ° C and 20% forging. , (C) 1600 ° C., 20% forging processing is performed, processing recrystallization is performed, and a structure in which grain growth is caused is shown.
As shown in FIG. 2, the sample before the Nb-19.4 at% Al deformation had a dendrite structure because Nb ₃ Al was precipitated by the peritectic reaction from the Nb solid solution and the liquid. 14
By hot working at 00 ° C., a structure in which Nb solid solution is finely precipitated in the Nb ₃ Al matrix phase is formed. The size of the Nb solid solution was 3 μm, and the average interval was 8 μm. 1
When deformed at 600 ° C, the second phase Nb solid solution is N
Although dispersed in the b ₃ Al matrix, the structure became coarser than at 1400 ° C. The size of the precipitate of the Nb solid solution was 10 μm, and the average interval was 15 μm. The toughness was evaluated by observing the room temperature hardness of the Nb-Al-based intermetallic compound having the structure obtained by hot working and the presence or absence of cracks in the hardness test. The results are shown in Table 1.

[0010]

[Table 1]

[0011]

INDUSTRIAL APPLICABILITY In the Nb-Al group intermetallic compound whose structure is controlled by the present invention, the microcracks introduced during dissolution are completely eliminated. Furthermore, the hot working causes the cast structure dendrite to be processed and recrystallized into fine crystal grains. In the Nb-Al-based intermetallic compound having this structure, the occurrence of cracks due to the indentation of the micro hardness meter was suppressed and the toughness at room temperature was improved, as compared with the ingot material.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between deformation stress and deformation temperature during hot working of a Nb-19.4 at% Al sample,

FIG. 2 is a structure (a) after heat treatment of Nb-19.4 at% Al at 1600 ° C. for 24 hours, forging is performed at 1400 ° C. and 20%, and Nb solid solution is finely divided into a Nb ₃ Al matrix phase by processing recrystallization. It is a schematic diagram of a photograph of a dispersed structure (b), 1600 ° C., 20% forging processing, processing recrystallization, and grain growth (c).

Claims (2)

[Claims] 1. A Nb—Al-based intermetallic compound containing 13% or more and 25% or less of Al in atomic% is hot-worked in a temperature range of 1200 ° C. or more and 1600 ° C. or less in a vacuum or an inert gas atmosphere. A method for controlling a structure of an Nb-Al-based intermetallic compound, which comprises subjecting the material to processing and recrystallization. 2. The method for controlling the structure of an Nb-Al intermetallic compound according to claim 1, wherein the hot working is forging.