JP2021121690A - TiAl-based alloy and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a TiAl-based alloy having excellent mechanical strength and a method for producing the same.
SOLUTION: The TiAl-based alloy according to the present disclosure _{contains a lamellar structure in which α 2} phase and γ phase are laminated, and has an oxygen content of 1000 mass. ppm or more 4600 mass. It is less than ppm. By setting the oxygen content in the above range, a TiAl-based alloy having excellent mechanical strength can be obtained. Further, TiAl based alloy according to the present disclosure, the difference between the Vickers hardness of alpha ₂ phase to the γ phase is + greater than 1.7 GPa + 2.9 GPa or less, preferably rigid than + 2.6 GPa.
[Selection diagram] FIG. 7

Description

The present disclosure relates to a TiAl-based alloy and a method for producing the same.

Methods for producing TiAl-based alloys include casting, forging and powder metallurgy. Powder metallurgy includes a metal powder injection molding method (MIM method) and a three-dimensional laminated molding (AM) method.

The MIM method is a manufacturing method in which a feedstock (molding material), which is a mixture of metal powder and a binder (binder), is injection-molded into a mold, and parts are molded by degreasing and sintering. Are suitable.

Patent Document 1 discloses a technique for producing a sintered body having a shape similar to that of a final product of a turbine wheel by the MIM method.

Japanese Unexamined Patent Publication No. 2011-174096 (Claim 1 and paragraph 0036)

As described in Patent Document 1, it is considered that the mechanical strength decreases as the oxygen content of the sintered body increases. Since the TiAl-based alloy has a high affinity for oxygen, the amount of oxygen mixed tends to be larger than that of other refractory metals.

Since the MIM method uses a binder, the amount of oxygen mixed tends to be larger than that of forging and casting.

The present disclosure has been made in view of such circumstances, and an object of the present disclosure is to provide a TiAl-based alloy having excellent mechanical strength and a method for producing the same.

TiAl based alloy according to the present disclosure include a lamellar tissue and alpha ₂ phase and γ-phase are stacked, oxygen content 1000Mass. ppm or more 4600 mass. It is less than ppm.

The method for producing a TiAl-based alloy according to the present disclosure has an oxygen content of 1000 mass. ppm or more 4600 mass. The amount of oxygen contained in the manufacturing process is controlled so as to be ppm or less.

According to the present disclosure, by setting the oxygen content in the above range, a TiAl-based alloy having excellent mechanical strength can be obtained.

It is a flowchart which illustrates the flow of manufacturing of the TiAl-based alloy by the MIM method. It is a phase diagram of a TiAl-based alloy (44at.% Al) in consideration of the oxygen content. It is an isothermal sectional view of Ti-Al-Cr at 1373K. It is a schematic diagram of the structure of a hypoxic alloy. It is a schematic diagram of the structure of a high oxygen alloy. It is a figure which shows the oxygen content in each phase (β phase, α _{2 phase and γ phase).} It is a figure which shows the change of hardness with the increase of oxygen. It is a schematic diagram of the growth of a crack in the lamellar structure (small difference) of the (α _{2 + γ) phase.} It is a schematic diagram of the growth of a crack in the lamellar structure (large difference) of the (α _{2 + γ) phase.} It is a schematic diagram of the structure observed about the test piece B. It is a schematic diagram of the structure observed about the test piece C. It is a figure which shows the ductility of the test piece A to C. It is a figure which shows the breaking strength of the test piece A to C. It is a figure which shows the destructive toughness of the test pieces A to C.

The present disclosure can be applied to low-pressure turbine blades of gas turbine engines, high-pressure compressor blades of gas turbine engines, turbine wheels of turbochargers, and the like.

Hereinafter, an embodiment of the TiAl-based alloy and the method for producing the same according to the present disclosure will be described with reference to the drawings.

The TiAl-based alloy according to this embodiment contains 1000 mass of oxygen. ppm or more 4600 mass. ppm or less, preferably 1000 mass. ppm or more 3000 mass. Contains ppm or less.

The TiAl-based alloy is an alloy composed of an intermetallic compound of Ti and Al. The TiAl-based alloy contains Ti and Al as main components. The "main component" is a component contained in a large amount. The TiAl-based alloy is 42 at. % Or more 49 at. It contains less than% Al, and most of the others are Ti.

The TiAl-based alloy preferably contains a third element, or a β-stabilizing element as the third and fourth elements. The β-stabilizing element is at least one of Cr, Nb, V, Mn, and Mo, and a plurality of β-stabilizing elements may be added in combination. The β-stabilizing element is 3 at. % Or more 11 at. % Or less, preferably 4 at. % Or more 10 at. % Or less should be included.

The TiAl-based alloy may contain Ni, C, and Si. Ni is 0.1 at. % Or more 1.0 at. %, Below, C is 0.1 at. % Or more 0.4 at. % Or less, Si is 0.2 at. % Or more 0.5 at. % Or less should be included. The TiAl-based alloy may contain unavoidable impurities such as N and Fe.

TiAl based alloy includes lamellar tissue and alpha ₂ phase and γ-phase are stacked. Vickers hardness of alpha ₂ phase than γ phase + greater than 1.7 GPa + 2.9 GPa or less, preferably rigid than + 2.6 GPa.

Next, a method for producing a TiAl-based alloy according to this embodiment will be described.

The method for producing a TiAl-based alloy according to the present embodiment includes a step of controlling the amount of oxygen contained in the production process. In this step, the oxygen content of the TiAl-based alloy was 1000 mass. ppm or more 4600 mass. ppm or less, preferably 1000 mass. ppm or more 3000 mass. The amount of oxygen is controlled so as to be ppm or less.

In _{this step, a lamellar structure in which the α 2} phase and the γ phase are laminated is formed, and _{the difference in Vickers hardness of the α 2} phase with respect to the γ phase is larger than +1.7 GPa and +2.9 GPa or less, preferably 2. It is desirable to control the oxygen content so that it is 6.6 GPa or more and + 2.9 GPa or less.

The TiAl-based alloy can be produced, for example, by a casting method in which melting and casting with a ceramic crucible or a metal powder injection molding (MIM) method.

<Casting method>
In the case of manufacturing by the above casting method, first, metal powder (Ti powder, Al powder, β-stabilizing element powder, etc.) as a raw material is put into a ceramic crucible or an induction melting furnace and melted in an inert gas atmosphere. A cast is obtained by pouring a molten metal material into a mold and cooling to room temperature.

The amount of oxygen contained (mixed) in the manufacturing process can be controlled by adjusting the amount of _{TiO 2 used as a raw material.}

<MIM method>
FIG. 1 is a flowchart illustrating a flow of manufacturing a TiAl-based alloy by the MIM method.
The method for producing a TiAl-based alloy by the MIM method shown in FIG. 1 includes steps of (S1) kneading and granulation, (S2) injection molding, (S3) degreasing, (S4) sintering, and (S5) heat treatment.

Metal powders and binders are used in the production of TiAl-based alloys.

The metal powder used as a raw material includes Ti powder and Al powder. The metal powder may contain powders of β-stabilizing elements as the third element, or the third and fourth elements. Further, the metal powder may contain Ni, C and Si.

The metal powder may be a powder produced by a gas atomizing method, a water atomizing method, a rotating electrode method or the like. The metal powder is preferably a powder produced by the gas atomization method.

The particle size of the metal powder is preferably 45 μm or less, preferably 30 μm or less. If the upper limit is exceeded, the fluidity of the molding material during injection molding becomes low, and filling defects are likely to occur. In addition, the voids between the powders become large and the density of the sintered body decreases. For example, as the metal powder, a powder prepared by the gas atomizing method and adjusted to an average particle size of 45 μm or less by classification can be used.

The binder is a piece of raw material powder that is joined together. The binder may be any material that can impart fluidity (viscosity) to the injection molding material so that the injection molding material is completely filled inside the mold during (S3) injection molding. The binder is a powder made of an organic material such as polyacetal, polypropylene, polyethylene, ethylene vinyl acetate, or an acrylic resin.

The raw material may further contain wax or other lubricants and the like.

(S1) Kneading and Granulation The metal powder and binder as raw materials are put into a kneader and kneaded while being pressurized and heated. The clay-like kneaded product is subjected to a granulation machine to obtain pellets (injection molding material).

The amount of the binder added is preferably about 30 wt% or more and 45 wt% or less of the entire kneaded product. The amount of binder added is adjusted according to the alloy composition, product shape, and mass production specifications in consideration of injection moldability and sinterability. The amount of oxygen contained in the final product varies depending on the alloy raw material, the type of binder, and the manufacturing conditions. In this embodiment, approximately 1000 mass. Add the binder in such an amount that a high oxygen alloy product of ppm or more is formed.

(S2) Injection Molding The injection molding material is put into an injection molding machine, plasticized, and injection molded into the cavity of the mold. As a result, a molded product (green body) having a desired shape can be obtained.

(S3) Solvent degreasing The green body is placed in a furnace and heated under reduced pressure and in a gas atmosphere to volatilize the binder (heat degreasing). The furnace may be either batch or continuous. As a result, a brown body from which the binder has been removed is obtained. When a gas is used here, it may be argon, nitrogen, nitric acid gas or the like.

The heat degreasing is carried out at a temperature at which the metal powders are not bonded to each other. Although it depends on the binder component and the pressure, it can be carried out at a temperature at which the binder of about 333K or more and 873K or less (60 ° C. or more and 600 ° C. or less) volatilizes. The heating is carried out at a temperature lower than that of sintering.

The degreasing may be carried out by a known degreasing method using a solvent, or may be combined with heat degreasing. In that case, the green body is immersed in a solvent to extract the binder (solvent degreasing). Depending on the binder component to be extracted, an organic solvent or water can be used as the solvent. The implementation temperature can be from room temperature to below the boiling point of the solvent.

(S4) Sintering Sintering is carried out in one or two steps. Here, a case where the implementation is carried out in two stages will be described.

First, the brown body is tentatively sintered to obtain a tentatively sintered body. Next, the temporary sintered body is main-sintered to obtain a sintered body.

In the tentative sintering, the metal particles are loosely bonded (necked) to each other. The tentative sintering is carried out at a temperature higher than the heating of degreasing and lower than the main sintering. For example, the tentative sintering temperature can be carried out at about 1323 K or more and 1523 K or less (1050 ° C. or more and 1250 ° C. or less), although it depends on the alloy component. If the tentative sintering temperature is less than 1323 K, necking becomes insufficient and the shape cannot be maintained. If the sintering temperature is higher than 1523K, there is a concern that sintering will partially proceed and unplanned shrinkage deformation will occur. Temporary sintering can be carried out with a holding time of 30 minutes or more and 2 hours or less.

The main sintering is carried out at a higher temperature than the temporary sintering. For example, the present sintering temperature can be carried out at 1523 K or more and 177 K or less (1250 ° C. or more and 1500 ° C. or less). Although it depends on the alloy component, if the main sintering temperature is less than 1523 K, the sintering becomes insufficient, a large number of voids remain, and there is a possibility that a sufficient sintering density cannot be reached. If the main sintering temperature is higher than 1773 K, there is a concern that a dissolution reaction may occur in a part of the sintering temperature and the planned shape cannot be maintained. This sintering can be carried out with a holding time of approximately 1 hour or more and 8 hours or less.

(S5) Heat treatment If necessary, the sintered body is heat-treated by a hot hydrostatic press (HIP) method. The heat treatment may be performed at a temperature about 323 K or more and 473 K or less (50 ° C. or more and 200 ° C. or less) lower than the sintering temperature, and at a high pressure of about 100 MPa or more and 180 MPa or less. As a result, internal defects such as voids disappear, and a healthier sintered body can be obtained.

After the HIP treatment, the sintered body may be held at the HIP treatment temperature or lower for a predetermined time.

The amount of oxygen contained (mixed) during the manufacturing process depends on the amount of oxygen contained in the metal powder as a raw material, the amount of oxygen contained in the binder, and the amount of oxygen in the atmosphere. In the MIM method, a low oxygen raw material is used, sufficient degreasing is performed, and sintering is performed in an inert gas to reduce the amount of oxygen mixed in by 1000 mass. ppm to 3000 mass. It is also possible to adjust to ppm.

Hereinafter, the effects of the TiAl-based alloy and the method for producing the same according to the present embodiment will be described.

As described in Patent Document 1, the amount of oxygen contained in the sintered body greatly affects the strength of the sintered body. Oxygen has a high affinity for TiAl-based alloys. Conventionally, many people think that ductility and strength (proof stress and breaking strength) decrease as the amount of oxygen mixed increases. For example, it has been announced that the ductility and strength (proof stress and fracture strength) of Fe, V, and B-added TiAl-based alloys decrease as the amount of dissolved oxygen increases.

On the other hand, the present inventors have found that the mixing of a predetermined amount of oxygen can improve the mechanical strength of the TiAl-based alloy.

(State diagram)
FIG. 2 shows a phase diagram of a TiAl-based alloy (44 at.% Al) in consideration of the oxygen content. In the figure, the vertical axis represents temperature (K) and the horizontal axis represents Cr content (at.%). FIG. 3 shows an isothermal sectional view of Ti—Al—Cr at 1373K.

In FIGS. 2 and 3, the solid line shows the oxygen content of 0.13 at. % (500 mass. ppm), the broken line indicates the oxygen content of 0.5 at. % (2,300 mass.ppm), the alternate long and short dash line has an oxygen content of 1.0 at. It is a line considering% (4,600 mass.ppm). In FIGS. 2 and 3, the oxygen content is 0.13 at. % Is "no oxygen added (0.13O)", oxygen content 0.5 at. % Is "+ 0.5O", oxygen content is 1.0 at. % Is expressed as "+1.0". The oxygen content of 0.75 at. When% is converted into a concentration, 3000 mass. It becomes ppm.

As can be seen from FIG. 2, in the high temperature region, the β phase and the α phase are the main constituent phases.
When the β phase is cooled, it transforms into the α phase, and when the α phase is cooled, it transforms into the γ phase. alpha ₂ phase precipitated in lamellar in γ phase the γ phase is cooled. As a result, a plurality of lamellar colonies (lamellar tissues) are formed. A lamella colony is a region in which the directions of the lamella are aligned. Since the lamella colonies have different directions of lamella, they are distinguished by a boundary even in metallographic observation.

The practical temperature range of the TiAl-based alloy is about 1173K (900 ° C.) from room temperature. According to FIG. 2, in the practical temperature range, the structure of the TiAl-based alloy is mainly composed of the (α ₂ + γ) phase. The (α ₂ + γ) phase is a phase in which an α ₂ phase (α ₂ plate) and a γ phase (γ plate) are mixed.

As the Cr content increases, a phase configuration containing a β phase can be formed even at a lower temperature. This is because the β phase can be stably present by adding Cr. The same tendency is shown when another β-stabilizing element is added instead of Cr.

According to FIG. 2, as the oxygen content increases, the transformation temperature range of each phase shifts. As can be seen from FIGS. 2 and 3, the _{region in which the (α 2} + γ) phase can stably exist increases by increasing the oxygen content. _{A transformation from the α phase to the (α 2} + γ) phase can occur even if the amount of Cr content added is slightly increased as compared with the case where the oxygen content is low.

(Tissue observation)
A low oxygen alloy (forged material, Ti-45Al-6Cr-0.13O (at.%)) And a high oxygen alloy (MIM material, Ti-44Al-4Cr-0.75O (at.%)) Are manufactured and SEM. The tissue was observed and modeled. FIG. 4 is a schematic view of the structure of the hypoxic alloy. FIG. 5 is a schematic view of the structure of the high oxygen alloy.

In the hypoxic alloy, the (α ₂ + γ) phase and the (γ + β) phase were observed. The (α ₂ + γ) phase _{formed lamella colonies in which α 2} plates and γ plates were alternately arranged. The β phase remained in the (α _{2 + γ) phase.}

In the hyperoxygen alloy, (α ₂ + γ) phase and γ grains were observed. In the high oxygen alloy, _{the lamellar structure of the (α 2} + γ) phase was more stable than in the low oxygen alloy. γ grains were produced between lamella colonies.

As shown in FIG. 5, in the structure of the hyperoxygen alloy, fine dispersion of the β phase between the lamella colonies _{of the (α 2 + γ) phase was observed.} The fine dispersion of the β phase causes precipitation strengthening, which leads to improvement in ductility and strength of the TiAl-based alloy.

(Oxygen content and hardness of each phase)
TiAl-based alloys (test pieces 1 to 3) having different oxygen contents were prepared, and the following studies were conducted.
Test piece 1 (0.13O): Ti-41Al-2.5Cr-0.13O (at.%)
Test piece 2 (0.5O): Ti-44Al-4Cr-0.5O (at.%)
Test piece 3 (1.0O): Ti-44Al-4Cr-1.0O (at.%)

The test piece 1 is a forged material produced by a forging method. The metal material was kept at a high temperature of 1573 K (1300 ° C.) in the heating furnace and then taken out from the heating furnace. In the cooling process, stationary forging was carried out with a forging machine. The strain rate was 30 mm / sec. The obtained forged material was held at 1673 K for 30 minutes, then cooled with water, and then subjected to aging heat treatment at 1373 K for 720 hours.

Test pieces 2 and 3 are MIM materials manufactured by the MIM method. Specimen 2 was sintered at 1653K for 2 hours and then HIP-treated at 1523K for 2 hours. The test piece 3 had the same manufacturing process as the test piece 2 up to HIP, and was further subjected to a low temperature heat treatment of holding at 1273 K for 16 hours. The oxygen content of the test pieces 2 and 3 is different as described above due to the difference in the amount of _{TiO 2} used as the raw material.

_{FIG. 6 shows the oxygen content in each phase (β phase, α 2} phase and γ phase) of the test pieces 1 to 3 (1373K). In the figure, the vertical axis is phase oxygen (at.%). The oxygen content in each phase was measured by soft X-ray spectroscopy using a soft X-ray spectrometer.

According to FIG. 6, oxygen (O) are mainly allocated to the alpha ₂ phase and the β phase and γ-phase was found that not very allocation.

FIG. 7 shows the change in hardness of the test pieces 1 to 3 (1373K) with increasing oxygen. In the figure, the vertical axis is Vickers hardness (GPa).

According to FIG. 7, as the oxygen content in the specimen is increased, it increased Vickers hardness of alpha ₂ phase. On the other hand, in the test pieces 1 to 3, the Vickers hardness of the γ phase hardly changed. This result is considered to be related to the amount of oxygen distributed to each phase. That is, in the oxygen distribution is often alpha ₂ phase increases the accompanied Vickers hardness to increase the oxygen content, oxygen Vickers hardness was hardly changed in almost not allocated γ phase.

alpha ₂ phase and γ-phase and the difference between the Vickers hardness (Delta] HV) is about 1.7GPa in specimen 1, about 2.6GPa the test piece 2 was about 2.9GPa in specimen 3. According to FIG. 7, by increasing the oxygen content of the TiAl based alloy, it was found that the ΔHv between alpha ₂ phase and γ-phase increases. This result suggests that the greater the difference in the mechanical properties of the alpha ₂ phase and γ-phase.

8 and 9 are schematic views of crack growth in the _{(α 2 + γ) phase lamellar tissue.} FIG. 8 shows crack growth in a lamellar tissue with a small ΔHv. FIG. 9 shows the crack growth in the lamellar tissue where ΔHv is larger than that in FIG.

When ΔHv is small, the cracks tend to grow linearly in the lamella colonies and show low fracture toughness. On the other hand, if the ΔHv is large, Taki entered the hard and brittle α ₂ phase cleft, a tendency to develop the interface between the γ-phase becomes strong. This complicates the crack growth path. As a result, the energy required for destruction increases and the toughness of destruction improves.

(Tissue and mechanical properties)
Test piece A, test piece B, and test piece C were prepared, and the following studies were conducted.
Specimen A: Ti-45Al-6Cr-0.13O (with low temperature heat treatment)
Specimen B: Ti-44Al-4Cr-0.75O (without low temperature heat treatment)
Test piece C: Ti-44Al-4Cr-0.75O (with low temperature heat treatment)

The test piece A is a forged material produced by a forging method. The metal material was kept at a high temperature of 1573 K (1300 ° C.) in the heating furnace and then taken out from the heating furnace. In the cooling process, stationary forging was carried out with a forging machine. The strain rate was 30 mm / sec. The obtained cast was held at 1673 K for 30 minutes, then cooled with water, and then subjected to aging heat treatment at 1373 K for 720 hours.

The test pieces B and C are MIM materials manufactured by the MIM method. It was sintered at 1653K for 2 hours and then HIP-treated at 1523K for 2 hours. The test piece C was further subjected to a low temperature heat treatment held at 1273 K for 16 hours.

The tissues of test pieces A, B, and C were observed by SEM. FIG. 10 shows a schematic diagram of the tissue observed for the test piece B. FIG. 11 shows a schematic diagram of the tissue observed for the test piece C.

In the test piece A, the surface integral of the lamellar tissue in the _{(α 2} + γ) phase was lower than that in the test pieces B and C (not shown). That is, by increasing the oxygen content, the interview rate of the lamellar tissue increased. Lamellar tissue has higher ductility and fracture strength than other tissues. Therefore, an increase in the interview rate of the lamellar structure leads to an improvement in ductility and fracture strength of the TiAl-based alloy.

According to FIG. 10, almost no γ grains were observed in the tissue of the test piece B. On the other hand, according to FIG. 11, in the tissue of the test piece C, γ grains were observed between the lamella colonies. From this, it was shown that γ grains grow by further heat treatment after the HIP treatment.

(Ductility)
FIG. 12 shows the ductility of the test pieces A to C. In the figure, the vertical axis is ductility, ε (%).

The ductility of test piece A was the lowest, and the ductility of test piece C was the highest. Since the test pieces B and C contain more oxygen than the test pieces A, it is considered that the surface integral of the lamellar tissue is increased, and as a result, the ductility is increased.

Specimens B and C contained the same amount of oxygen, but Specimen C showed higher ductility. It is considered that this is because the γ grains grew and the ductility was improved by performing an appropriate heat treatment after the HIP treatment. gamma particle (gamma phase) is softer than the alpha ₂ phase is a phase responsible for the deformation of the TiAl based alloy.

(Breaking strength)
FIG. 13 shows the breaking strength (UTS) of the test pieces A to C. In the figure, the vertical axis is the breaking strength and σ _UTS (MPa).

The test piece B, which is a MIM material, had a lower breaking strength than the test piece A, which is a forged material. On the other hand, the test piece C, which is the same MIM material as the test piece B, showed a higher breaking strength than the test pieces A and B.

The breaking strength tends to increase as the particles become finer. It is considered that the breaking strength of the test piece B was lowered because the MIM method could not make the particles as fine as the forging method. On the other hand, in the test piece C in which the test piece B was further heat-treated at a low temperature, it is considered that the breaking strength was increased because the γ phase (γ grains) having high ductility was precipitated.

(Destructive toughness)
FIG. 14 shows the destructive toughness of the test pieces A to C. In the figure, the vertical axis represents the _K IC ^{(MPam 0.5).}

According to FIG. 14, the fracture toughness was lowest in test piece A and highest in test piece B. As described above, by increasing the oxygen content, in addition to high lamellar structure area fraction of the fracture toughness rises, the difference in Vickers hardness between the alpha ₂ phase and γ-phase increases, the crack propagation It is probable that the destructive toughness of the test pieces B and C became higher due to the complexity of.

Specimen C was less destructive toughness than Specimen B. As described above, in the test piece C, γ grains are precipitated. The grains do not act as a resistance to crack growth. Therefore, it is considered that the test piece C has a lower fracture toughness than the test piece B as the surface integral of the lamellar structure decreases with the precipitation of γ grains.

<Additional notes>
The TiAl-based alloy described in the above-described embodiment and the method for producing the same are grasped as follows, for example.

TiAl based alloy according to the present disclosure include a lamellar tissue and alpha ₂ phase and γ-phase is complexed in layers, oxygen content 1000Mass. ppm or more 4600 mass. It is less than ppm.

When the oxygen content is in the above range, _{the lamellar structure of the (α 2} + γ) phase is stabilized. Lamella tissue is a tissue with relatively high ductility. Therefore, the ductility of the TiAl-based alloy is improved.

When the total oxygen content is increased, the increased oxygen content _{is mainly distributed to the α 2} phase and not so much to the γ phase _{when transforming from the α phase to the (α 2} + γ) phase. When oxygen is often distributed, alpha ₂ phase becomes hard, the ductility is reduced. On the other hand, even if the total oxygen content is increased, the oxygen distribution to the γ phase does not increase so much, so that the decrease in ductility is small. Thus, the difference in the mechanical properties of the alpha ₂ phase and γ-phase is relatively large.

In one aspect of the disclosure, it is desirable that the difference between the Vickers hardness of the alpha ₂ phase to the γ phase is not more than + greater than 1.7 GPa + 2.9 GPa.

If the difference in the mechanical properties of the alpha ₂ phase and γ-phase is small, the crack to become stronger tendency to progress linearly within lamellar colonies, indicating a low toughness. On the other hand, if _{the difference in mechanical properties between the α 2} phase and the γ phase is large, the crack tends to develop at the interface between _{the α 2 phase and the γ phase.} This complicates the crack growth path. As a result, the energy required for destruction increases and the toughness of destruction improves.

alpha ₂ phase than other phases, low originally fracture toughness. Therefore, the effect of increased oxygen distribution in alpha ₂ phase has on the ductility and fracture strength of the whole TiAl based alloy is small.

In one aspect of the above disclosure, β-stabilizing elements may be included.

In a TiAl-based alloy containing a β-stabilizing element, a β phase may be present in a practical temperature range (room temperature to 1173K). That is, the β phase can be finely dispersed at the lamella interface of _{the (α 2 + γ) phase.} Since the fine dispersion of the β phase causes precipitation strengthening, the ductility and breaking strength of the TiAl-based alloy are improved.

The method for producing a TiAl-based alloy according to the present disclosure has an oxygen content of 1000 mass. ppm or more 4600 mass. The amount of oxygen contained in the manufacturing process is controlled so as to be ppm or less.

In one aspect of the disclosure, further and alpha ₂ phase and γ-phase is formed by lamellar tissue laminate, the difference in Vickers hardness of the alpha ₂ phase to the γ phase is + greater than 1.7 GPa + 2.9 GPa It is desirable to control the amount of oxygen contained in the manufacturing process so as to be as follows.

In one aspect of the above disclosure, a metal powder injection molding method can be used.

In one aspect of the above disclosure, a casting method in which melting and casting with a ceramic crucible may be used.

By adopting the above method, a TiAl-based alloy having a desired oxygen content can be obtained.

In one aspect of the above disclosure, a β-stabilizing element may be added.

Claims (8)

and alpha ₂ phase and γ phase comprises a composite lamellar tissue in layers,
Oxygen content is 1000 mass. ppm or more 4600 mass. TiAl-based alloy of ppm or less. TiAl based alloy of claim 1 difference in Vickers hardness of the alpha ₂ phase + is greater + 2.9 GPa or less than 1.7GPa for the γ-phase. The TiAl-based alloy according to claim 1 or 2, which contains a β-stabilizing element. Oxygen content is 1000 mass. ppm or more 4600 mass. A method for producing a TiAl-based alloy, which controls the amount of oxygen contained in the production process so as to be ppm or less. Furthermore, alpha ₂ phase and lamellar tissue γ phase and are stacked is formed, the alpha as the difference between the Vickers hardness of the _two phases is equal to or less than + greater than 1.7 GPa + 2.9 GPa for the γ-phase, production The method for producing a TiAl-based alloy according to claim 4, wherein the amount of oxygen contained in the step is controlled. The method for producing a TiAl-based alloy according to claim 4 or 5, wherein a metal powder injection molding method is used. The method for producing a TiAl-based alloy according to claim 4 or 5, wherein a casting method of melting and casting with a ceramic crucible is used. The method for producing a TiAl-based alloy according to any one of claims 4 to 7, wherein a β-stabilizing element is added.

Images