JPH04365829A - Tial-based intermetallic compound and production thereof - Google Patents

Abstract

PURPOSE:To provide the alloy having excellent strength and ductility at a high temp. by controlling the phase, structure and crystal grain size of the TiAl-based intermetallic compd. CONSTITUTION:This TiAl-based intermetallic compd. consists basically of 45% to 50% Al by atomic % and the balance Ti and is formed by producing a beta phase in equiaxial grains consisting of at least 1 kind of the elements selected from additive element groups of Nb, Mo, V or Mn, at >=1% and <=5% by atomic % and consisting of a gamma phase and alpha2 phase. This process for production of the TiAl-based intermetallic compd. consists in dissolving the intermetallic compd. having the above-mentioned components, then heat treating the soln. for >=48 hours at >=1000 deg.C and <=1250 deg.C and subjecting the soln. to hot working at <=1100 deg.C and <=1350 deg.C and to >=40% deforming at <=1X10<-2>/s straining rate to precipitate the beta phase at the grain boundaries of the equiaxial grains consisting of the gamma phase and the alpha2, phase, thereby improving the ductility and strength at the high temp.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a TiAl intermetallic compound that is promising as a heat-resistant material and a method for producing the same. TiAl intermetallic compounds have high specific strength and are considered to be applied as high-temperature heat-resistant materials to engine parts, various rotating bodies, and aircraft.

0002

[Prior Art] TiAl intermetallic compounds show a positive temperature dependence in that their strength increases as the temperature rises, and they also have a specific gravity of 3.9, making them a lightweight heat-resistant material that has been researched and developed with the aim of applying them to aircraft. has been done. However, TiAl intermetallic compounds are characterized by poor deformability compared to general metal alloys, and many studies have been conducted on improving ductility at room temperature. Ti-34.1 is an example of alloy design by adding a third element to improve ductility at room temperature.
wt%Al-34wt%V alloy (U.S. Pat. No. 42946
No. 15), Ti-41.7% by weight Al-10% by weight Ag
There is an alloy (Japanese Unexamined Patent Publication No. 58-123847). moreover,
An example of improving the ductility at room temperature to 2 to 3% by adding Mn to a TiAl intermetallic compound (Japanese Patent Application Laid-Open No. 61-41740
), Cr addition (US Pat. No. 4,842,819), Ta
addition (US Pat. No. 4,842,817) and Si addition (US Pat. No. 4,836,983). In the quaternary system, Ti52-42 is an example of improved ductility and oxidation resistance at room temperature.
There is Al46-50 Cr1-3 Nb1-5 (Japanese Unexamined Patent Publication No. 2-25534).

[0003] The TiAl intermetallic compound has a ductility of 3 at room temperature.
% or less and difficult to process at room temperature, methods are used to give the shape using precision casting technology or powder technology. Furthermore, superplastic working at high temperatures is being considered as a shape imparting technology. After forming, the TiAl intermetallic compound is applied as a high-temperature structural member to areas where high-temperature strength is required. In response to these demands, there is a need to design materials for intermetallic compounds that have excellent workability at high temperatures and high strength. It has a γ+α2 structure, and Nb, Cr, Mo, and V are added as the alloy component system, and further B and Si are added.
An example has been published in which high-temperature strength and room-temperature ductility were improved by adding a small amount of grain boundary strengthening element (JP-A-1-298)
No. 127). However, the elongation at 800°C is a maximum of 4%, and the workability at high temperatures has not been improved.

In addition to alloy design using additive elements, examples have been reported in which high-temperature ductility is improved by refining the structure through hot working (for example, Japan Institute of Metals Autumn Symposium Lecture Summary (1989), p. 245 ). Furthermore, the present inventors have reported an example in which ductility at high temperatures was significantly improved by adding Cr as a third element to precipitate β phase at grain boundaries (Japan Institute of Metals Autumn Conference Presentation Summary (1990) ) P.26
8). In order to improve workability and strength at high temperatures, it is necessary to control the structure by combining various processes such as melting, heat treatment, and processing heat treatment in addition to the effect of adding a third element.

[0005]

[Problems to be Solved by the Invention] The phase diagram of TiAl-based intermetallic compounds is not clear, and the phase diagram of TiAl-based intermetallic compounds is not clear.
Simply adding elements, melting, and casting cannot fully demonstrate its properties. It has been found that by subjecting Cr-added alloys to processing heat treatment, β phase precipitates at grain boundaries and improves ductility, but high-temperature strength is insufficient. The present invention systematically investigates the effects of added elements, performs alloy design based on phase diagrams, and performs processing heat treatment to control the phases, structures, and grain sizes that appear, and improve strength and ductility at high temperatures. It is an object of the present invention to provide a TiAl-based intermetallic compound.

[0006]

[Means for Solving the Problem] In a TiAl-based intermetallic compound in which Al is 45% to 50% by atomic% and the balance is Ti, V, Mn, Nb, or Mo is contained in an amount of 1% to 5% by atomic%. The purpose is to contain at least one selected element as an additive element, to precipitate the β phase between the equiaxed grains of the γ phase and the α2 phase, with the γ phase as the main phase, and to improve strength and ductility at high temperatures. TiAl-based intermetallic compound for which alloy design was conducted.

[0007] This compound contains V, Mn as additive elements.
, Nb, and Mo, and is subjected to post-melting heat treatment and further hot working in order to precipitate the β phase at the grain boundaries. Specifically, β
After melting, an alloy containing stabilizing elements (V, Mn, Nb, Mo) from 1% to 5% by atomic % and having a composition of 45% to 50% Al by atomic % and the balance Ti is heat-treated. 10
This is achieved by carrying out deformation of 40% or more at a temperature of 1100°C or more and 1350°C or less and a strain rate of 1×10-2 s-1 or less after cooling slowly for 48 hours or more at 00°C or higher and 1250°C or lower. Ru.

[0008]

[Operation] V, Mn, Nb, or Mo was added as an additive element to precipitate the β phase in the TiAl-based intermetallic compound. In the case of a TiAl binary alloy, an alloy with Al balance Ti of 50 atomic % or more becomes a γ single-phase alloy. Al content is 50 atomic%
% or less, if it is 30% or more, there will be two phases of γ + α2 phase,
If the Al content is 45% or more, the volume fraction of the α2 phase will be 30% or more, and the strength and ductility at room temperature will decrease. Therefore, Al
The amount is preferably 45% or more and 50% or less in atomic %. atom%
The structure after dissolution of the intermetallic compound consisting of an Al content of 45% to 50% and the remainder Ti becomes a layered structure (lamellar structure) in which γ and α2 exist alternately. In the Ti-Al binary alloy, the β phase exists as an equilibrium phase at temperatures above 1500° C., but the β phase cannot be frozen to room temperature even by rapid cooling. In order to generate the β phase, it is necessary to add a β phase stabilizing element to Ti and change the β phase region in the ternary phase diagram.

[0009] V, Mn, Nb, Mo in atomic %
An intermetallic compound containing 1% or more and 5% or less of Al, with an Al content of 45% or more and 50% or less, and the remainder Ti, has a γ+α2 layered structure (lamellar structure) and a γ It becomes a structure containing grains. No β-phase peak appears in X-ray diffraction. Ingot at 1000℃
When the heat treatment is performed at a temperature below 1250° C., the layered structure changes to a mixed crystal structure consisting mostly of equiaxed grains of γ grains and α2 grains. Even after annealing, the existing phases remain the γ phase and α2 phase. Regarding the annealing temperature, if the annealing temperature is 1000°C or lower, no effect of annealing is observed, and if the annealing is performed at 1250°C or higher, the crystal grain size becomes coarse or an acicular structure appears. When the annealing time was 48 hours or less, a layered structure remained and a homogeneous annealed material could not be obtained. By hot working a third element-added intermetallic compound that has a mixed crystal structure consisting of equiaxed grains of γ grains and α2 grains,
As the γ grains become finer, the β phase precipitates. Figure 1 shows the X-ray diffraction patterns of the annealed material and hot-processed material. As a comparative example, a pattern of a TiAl intermetallic compound having a stoichiometric composition is shown. Table 1 shows the effect of each additive element on phase stability on the TiAl intermetallic compound.

[0010] The TiAl intermetallic compound added with Mo is
A layered structure (lamellar structure) appears in the ingot material, a β phase is formed between the lamellar grains, and the β phase forming ability is high. The hot-worked Mo-added intermetallic compound had a mixed crystal structure of fine β crystal grains and γ equiaxed grains. The fine equiaxed grain structure had the effect of making the grain size finer, resulting in improved ductility at high temperatures. O mainly acts as a solid solution in the α phase to strengthen the α phase, so it is necessary to suppress O to 0.05% by weight or less.

From the TiAl binary system phase diagram, the β phase, which is stable at high temperatures, becomes the α phase below 1250°C, which does not exist at room temperature, but by adding an additive element that has a β stabilizing effect, the β region expands, and the β phase changes to the α phase at room temperature. can exist up to. Ti
The effect of forming the Al-based intermetallic compound into a multiphase structure having two or more phases is to suppress the growth of γ crystal grains and to make the crystal grains finer. Furthermore, the high temperature strength is low in the order of γ phase α2 phase β phase, and deformation is easy at high temperatures. The effect of converting phases with different strengths into multiple phases is that the easily deformable phase is responsible for deformation, and the high strength phase has the effect of increasing the strength. When the β phase, which is easily deformed at high temperatures, precipitates at the γ grain boundaries, it has the effect of significantly improving workability at high temperatures.

[0012] As a method for changing the structure, refining the structure by processing recrystallization is a method that is used for ordinary metals or alloys, but in the case of TiAl-based intermetallic compounds, it is possible to refine the structure by processing recrystallization. Materials range from room temperature to 800℃
It had almost no ductility and fractured brittlely. In the case of such difficult-to-process materials, it is difficult to use the conventional process-recrystallization method of processing at low temperatures, storing process strain energy, and recrystallizing by heat treatment. In order to refine the crystal grains and precipitate the β phase, in the ternary phase diagram, β
It is conceivable to process the material at a temperature higher than that at which the phase exists, and to utilize the dynamic recrystallization phenomenon in which deformation and recrystallization occur at the same time. In the dynamic recrystallization phenomenon, the important parameters are deformation temperature, strain rate during deformation, and amount of deformation. In other words, in order to refine the grains and precipitate the β phase by utilizing the dynamic recrystallization phenomenon, control of temperature and strain rate is particularly important, and a processing process that satisfies these conditions must be selected. .

[0013] Isothermal forging is the most useful process for deforming TiAl-based intermetallic compounds in a higher temperature range and at a lower strain rate than the α-β transformation, and controlling crystals by dynamic recrystallization. Isothermal forging is characterized by keeping the temperature of the mold and sample the same, and is used as a method for forming difficult-to-process materials. When the deformation temperature is increased and deformation is performed at a lower strain rate, the TiAl-based intermetallic compound is easily deformed, but there is a problem in obtaining the desired microcrystalline structure in which the β phase is precipitated. That is, when comparing the crystal grain sizes when the deformation temperature is 1250°C and 1100°C at the same strain rate, recrystallized grains tend to grow at 1250°C. However, when isothermal forging is performed at temperatures below 1000℃, fine crystal grains appear along with deformation bands.
There were unrecrystallized portions, resulting in a heterogeneous crystal structure.

In other words, appropriate conditions for temperature and strain in isothermal forging include a temperature of 1100°C or higher and a strain rate of 1×10
-2/s or less is desirable. Furthermore, the amount of deformation is 4
If it is less than 0%, an undeformed portion exists and the difference in grain size is large. In order to obtain homogeneous fine grains throughout the sample, the amount of deformation must be 40% or more, preferably 6 at a time.
A large deformation of 0% or more is required. In addition to isothermal forging, hot extrusion, hot rolling, etc. are possible as deformations that satisfy this deformation condition.

[0015] By the above forging method, V, Mn, Nb, M
As a result of constant temperature forging of 40% or more of the TiAl-based intermetallic compound to which o was added, the recrystallized structure became fine equiaxed grains, and a β phase precipitated as a second phase. When the β phase precipitates at the grain boundaries of the γ phase, the β phase has the effect of improving workability at high temperatures.

[0016]

【Example】

(Example 1) Ti-48at%Al-2at%Nb High purity titanium (99.9%) and aluminum (99.9%)
9%) was used as the melting raw material, and by plasma arc melting, 48at%Al-2at%Nb, the balance was Nb with Ti.
The added TiAl intermetallic compound was melted. 1050℃, 9
As a result of homogenization heat treatment in vacuum for 6 hours, the crystal grain size was 10.
Equiaxed grains of about 0 μm were formed. A sample with a diameter of 35 mm and a height of 42 mm was machined from a material subjected to homogenization heat treatment by electrical discharge machining. Isothermal forging is performed in a vacuum atmosphere with an initial strain rate of 5 x 10-4 s-1 and a heating temperature of 70% at 1300°C.
Pressed down. FIG. 2 shows a photograph of the crystal structure of the Nb-added TiAl-based intermetallic compound after forging. Average grain size 34μm
Equiaxed fine grains were obtained over a wide range. As a result of identifying the phase by X-ray diffraction from the isothermal forged sample, the phase precipitated at the grain boundaries showed a β phase diffraction peak. Gauge part thickness 2mm, width 2 from forged material with multi-wire saw
．． A tensile test piece with a diameter of 5 mm and a length of 11.5 mm was prepared, and a high temperature tensile test was conducted in a vacuum atmosphere. sample at 1200℃
A tensile test was conducted under the condition of a strain rate of 1 x 10-3/s, and the result showed an elongation of 353%.

(Example 2) Ti-48at%Al-2a
An intermetallic compound having a composition of t%Mo was prepared in a similar manner.
It was melted, homogenized, heat-treated, and worked, and subjected to phase and structure tests and high-temperature tensile tests. The component analysis results are shown in Table 1, and the test results are shown in Table 3.

(Example 3) Ti-48at%Al-2a
An intermetallic compound having a composition of t%V was melted, homogenized, and hot worked in the same manner, and subjected to phase and structure and high-temperature tensile tests. The component analysis results are shown in Table 1, and the test results are shown in Table 3.

(Example 4) Ti-48at%Al-2a
An intermetallic compound having a composition of t%Mn was prepared in a similar manner.
It was melted, homogenized, heat-treated, and worked, and subjected to phase and structure tests and high-temperature tensile tests. The component analysis results are shown in Table 1, and the test results are shown in Table 3.

(Example 5) Ti-49at%Al-1a
t%Mo High purity titanium (99.9%) and aluminum (99.9%)
9%) as the melting raw material, and as the third element, Mo as the atomic%
A 1% TiAl intermetallic compound was melted by non-consumable arc melting. As a result of homogenization heat treatment in vacuum at 1050° C. for 96 hours, equiaxed grains with a crystal grain size of about 100 μm were obtained. A sample was processed from a material that had been subjected to homogenization heat treatment and subjected to isothermal forging. The structure after isothermal forging had equiaxed γ-phase grains over a wide range. X-ray diffraction revealed that β phase was precipitated at a volume fraction of about 0.5%. Gauge part thickness 2mm, width 2.5 with multi-wire saw from forged material
A tensile test piece with a length of 11.5 mm and a length of 11.5 mm was prepared, and a high temperature tensile test was conducted at a strain rate of 1×10 −3 /s in a vacuum atmosphere. The test results are shown in Table 3.

(Example 6) Ti-46at%Al-4a
An intermetallic compound having a composition of t%Mo was prepared in a similar manner.
It was melted, homogenized, heat-treated, and worked, and subjected to phase and structure tests and high-temperature tensile tests. The test results are shown in Table 3.

(Example 7) Ti-45at%Al-5a
An intermetallic compound having a composition of t%Mo was prepared in a similar manner.
It was melted, homogenized, heat-treated, and worked, and subjected to phase and structure tests and high-temperature tensile tests. The test results are shown in Table 3.

(Example 8) Ti-49at%Al-2a
An intermetallic compound having a composition of t%Mo was prepared in a similar manner.
It was melted, homogenized, heat-treated, and worked, and subjected to phase and structure tests and high-temperature tensile tests. The test results are shown in Table 3.

(Example 9) Ti-47at%Al-2a
An intermetallic compound having a composition of t%Nb-1at%Mo was melted, homogenized, and hot worked in the same manner, and subjected to phase and structure and high-temperature tensile tests. The test results are shown in Table 3.

(Comparative Example 1) An intermetallic compound having a composition of Ti-50at%Al was melted, homogenized, and hot worked in the same manner, and subjected to a high-temperature tensile test on phase and structure. The test results are shown in Table 3.

(Comparative Example 2) An intermetallic compound having a composition of Ti-48at%Al was melted, homogenized and hot-processed in the same manner, and subjected to a high-temperature tensile test on phase and structure. The test results are shown in Table 3.

(Comparative Example 3) Ti-47at%Al-3a
An intermetallic compound having a composition of t%Cr was prepared in a similar manner.
It was melted, homogenized, heat-treated, and worked, and subjected to phase and structure tests and high-temperature tensile tests. The test results are shown in Table 3.

[0028]

[Table 1]

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Effect of the invention] As the third element, V, Mn, Nb, Mo
The β phase was precipitated by melting, homogenizing annealing, and processing heat treating the TiAl-based intermetallic compound to which . In particular, it has been revealed that for alloys containing V, Mn, and Nb, the β phase precipitates at grain boundaries, and the workability at high temperatures is significantly improved. The TiAl-based intermetallic compound of the present invention has excellent hot workability and can be processed into molded products of complex shapes, and has a wide range of industrial applications. For example, honeycomb structures can be manufactured using superplastic processing, which can be applied to reduce the weight of aircraft. By performing heat treatment after forming by hot working, it is possible to coarsen crystal grains and improve creep characteristics at high temperatures.

[Brief explanation of the drawing]

FIG. 1 is an X-ray diffraction pattern of a hot-processed TiAl-based intermetallic compound doped with V, Mn, Nb, and Mo.

FIG. 2 is a photograph of the crystal structure of the Nb-added TiAl-based intermetallic compound after forging.

Claims (2)

[Claims] Claim 1: In a TiAl-based intermetallic compound in which 45% to 50% of Al is based on Ti as a basis in atomic %, V
, Mn, Nb, or Mo in an amount of 1% or more and 5% or less in terms of atomic %, so that a β phase appears in equiaxed grains consisting of a γ phase and an α2 phase. , a TiAl-based intermetallic compound with improved ductility and strength at high temperatures. [Claim 2] In a TiAl-based intermetallic compound in which 45% to 50% of Al is based on Ti as a basis in atomic %, V
After melting an intermetallic compound containing at least 1% to 5% by atomic percent of at least one element selected from the additive element group of , Mn, Nb, or Mo, heat treatment is performed at 1000°C to 100°C.
After 48 hours or more at 250°C or lower and slow cooling, hot working was performed at 1100°C or higher and 1350°C or lower at a strain rate of 1 x 10-
A TiAl-based metal with improved ductility and strength at high temperatures, characterized by deformation of 40% or more at 2s-1 or less and precipitation of β phase at grain boundaries of equiaxed grains consisting of γ phase and α2 phase. A method for producing an intermediate compound.