Ti al alloy, method for deformation heat treatment and application

Abstract

The application discloses a TiAl alloy, a deformation heat treatment method and application, and the alloy is as follows: Ti-(43-48)Al-(0-8)X-(0-0.5)Z, wherein X is one or two or more of Nb, Mo, Cr, Ta, V and Mn elements; Z is one or two or more of Fe, C, N, O, B and Si elements; the alloy is a fine-grain duplex structure, the fine-grain duplex structure is composed of fine-size sheet group and equiaxial gamma grains; the size of the sheet group is 20-40 mu m, the size of the gamma grain is 10-20 mu m, and the volume fraction of the gamma grain is 30-60%; firstly, high-density crystal defects are generated in the original structure by controlling the deformation temperature, the deformation rate and the deformation amount of the pre-deformation treatment; and then, the fine-grain near-sheet structure or the duplex structure is obtained by controlling the holding temperature and the holding time in the isothermal heat treatment process.

Description

Technical Field

[0001] This invention relates to the field of high-temperature structural materials technology, specifically to a TiAl alloy, a deformation heat treatment method, and its application. Background Technology

[0002] TiAl alloys possess characteristics such as low density, high melting point, high specific strength, high creep strength, good oxidation resistance, and stable microstructure, making them a hot topic in the development of lightweight structural materials for aerospace equipment. They show great application potential in the temperature range of 650–1000℃. While TiAl alloys offer advantages of being lightweight and high-strength, their low room-temperature plasticity and insufficient processing and forming capabilities limit their widespread application. Research shows that for as-cast microstructures, plasticity can be significantly improved by reducing the grain size, indicating that microstructure refinement is a necessary condition for effectively improving alloy plasticity. Currently, without sacrificing the already excellent high-temperature properties of TiAl alloys, improving their room-temperature plasticity can often be achieved by refining the size of lamellar cluster grains. In conclusion, controlling the microstructure and refining the grain size of TiAl alloys are important means to improve their room-temperature plasticity.

[0003] Grain refinement can effectively improve the plasticity and machinability of alloys. Due to the intrinsic brittleness of γ-TiAl alloys, microstructure refinement has gradually become a research hotspot for improving their performance. Extensive research has been conducted on refining the microstructure of TiAl alloys through direct heat treatment. For example, CN103498065A discloses "A method for refining grains in TiAl alloys," which involves cyclic heat treatment in the solid-liquid two-phase region, with continuous melting and solidification, causing coarse as-cast structures to continuously form new nuclei and grow, thus achieving grain refinement. However, this method is cumbersome and time-consuming, requiring multiple cycles of heating and cooling around the liquidus temperature, significantly increasing the heat energy required for grain refinement. Furthermore, this method refines grains by remelting coarse columnar crystals, with the melted dendrites acting as new nucleation sites. This makes precise control of the cyclic heat treatment process parameters difficult. If the holding time in the liquid phase region is insufficient to form enough nucleation sites in the original coarse grains, and the holding time is long, the newly nucleated grains grow rapidly, failing to achieve the effect of grain refinement. For example, CN112048690A discloses "a deformation heat treatment method for controlling the fine grain structure of TiAl alloy", which uses pre-deformation treatment and isothermal heat treatment to refine the alloy grains. However, this method has a high pre-deformation temperature, and the deformation temperature is the lower part of the α single-phase region (Tα~Tα+40℃). The high deformation temperature means that the sample cools down during the process of taking it out of the heat treatment furnace and transferring it to the compressor after pre-holding. The actual deformation temperature is difficult to control during manual operation, and complex changes such as α recrystallization and γ-phase to α-phase phase transformation may occur simultaneously during the actual deformation process. Summary of the Invention

[0004] This invention addresses the problems existing in the prior art by providing a TiAl alloy, a deformation heat treatment method, and its application.

[0005] The technical solution adopted in this invention is: a TiAl alloy, wherein the alloy is as follows:

[0006] Ti-(43~48)Al-(0~8)X-(0~0.5)Z, wherein X is one or more of Nb, Mo, Cr, Ta, V, and Mn; Z is one or more of Fe, C, N, O, B, and Si; the alloy has a fine-grained bimorphic structure, which consists of fine-sized lamellar clusters and equiaxed γ grains; the lamellar cluster size is 20μm~40μm, the γ grain size is 10μm~20μm, and the volume fraction of γ grains is 30%~60%.

[0007] Furthermore, the alloy has a fine-grained near-lamellar structure, consisting of small-sized lamellar clusters and fine spherical γ grains dispersed on the boundaries of the lamellar clusters; the size of the lamellar clusters is 40 μm to 80 μm; the diameter of the γ grains is 5 μm to 10 μm, and the volume fraction of the γ grains is 5% to 30%.

[0008] A deformation-based heat treatment method for TiAl alloys includes the following steps:

[0009] Step 1: Hot isostatic pressing is applied to the TiAl alloy to obtain a dense TiAl alloy workpiece;

[0010] Step 2: Hold the alloy workpiece obtained in Step 1 at the upper temperature of the α2+γ phase region for time t1; then compress and deform the alloy workpiece, and after cooling, obtain the pre-deformed and compressed alloy workpiece; wherein the upper temperature of the α2+γ phase region Te–T≤deformation temperature<Te, and Te is the eutectoid temperature of α→α2+γ.

[0011] Step 3: Hold the pre-deformed and compressed alloy workpiece obtained in Step 2 at the upper temperature of the α+γ dual-phase region or the lower temperature of the dual-phase region for t2 time, and after cooling, obtain a fine-grained near-lamellar TiAl alloy or a fine-grained dual-phase structure.

[0012] The upper section of the α+γ two-phase region has a temperature range of Tα-1 / 2(Tα-Tγ) to Tα, and the lower section of the α+γ two-phase region has a temperature range of Tα-3 / 4(Tα-Tγ) to Tα-1 / 2(Tα-Tγ). Tα is the temperature at the boundary between the α single-phase region and the phase region containing α+γ phases, and Tγ is the lower limit temperature of the phase region containing α+γ phases.

[0013] Furthermore, in step 1, the hot isostatic pressing treatment temperature is 1160℃, the pressure is 140MPa, and the treatment time is 4h.

[0014] Furthermore, in step 2, the t1 time is 5 to 20 minutes, and the t2 time is 10 minutes to 24 hours.

[0015] Furthermore, in step 2, T is 100–300°C.

[0016] Furthermore, the cooling in steps 2 and 3 is performed using air cooling.

[0017] Furthermore, the amount of compression deformation in step 2 is 10% to 50%.

[0018] Furthermore, the compression deformation rate in step 2 is 0.05 cm·s. -1 ~0.005cm·s -1 .

[0019] An application of a TiAl alloy, wherein the TiAl alloy is used as a high-temperature structural material.

[0020] The beneficial effects of this invention are as follows:

[0021] (1) The present invention operates at a temperature slightly below the phase transition temperature (γ phase → α phase) and the order-no-transition temperature, so that only a few types and some γ recrystallizations of structural defects occur during the deformation process, accumulating deformation storage energy and nucleation sites for subsequent heat treatment processes.

[0022] (2) At the deformation temperature, the TiAl alloy has already undergone high-temperature softening and its plasticity is much higher than that at room temperature. When small deformation compression is performed at this temperature, the compressed sample is not easy to crack, and the microstructure control has high rationality and operability.

[0023] (3) The deformation process and heat treatment process of the present invention are both isothermal processes, and the control of the heating process and cooling process is not required;

[0024] (4) The present invention has high processing efficiency and simple operation steps. It can precisely control the microstructure characteristics of TiAl alloy, such as fiber structure type, lamellar / γ grain size / lamellar spacing and lamellar content, by controlling the deformation process and heat treatment process. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the process of the present invention.

[0026] Figure 2 This is a schematic diagram illustrating the process and principle of deformation heat treatment in this invention.

[0027] Figure 3The images show the microstructure of the alloy obtained in Example 1 of this invention, where a is a SEM image of the coarse-grained lamellar structure in the cast state without deformation heat treatment, b is a SEM image after hot isostatic pressing, c is a SEM image after pre-deformation treatment, and d is a high-magnification SEM image after pre-deformation treatment.

[0028] Figure 4 The images show the microstructure of the alloy obtained in Example 1 of this invention, where a is a SEM image of the fine-grained bimorphic structure after isothermal heat treatment at 1280℃ for 24h, and b is a SEM image of the fine-grained near-lamellar structure after isothermal heat treatment at 1320℃ for 24h. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] like Figure 1 As shown, a TiAl alloy is described below:

[0031] Ti-(43~48)Al-(0~8)X-(0~0.5)Z, wherein X is one or more of Nb, Mo, Cr, Ta, V, and Mn; Z is one or more of Fe, C, N, O, B, and Si; the alloy has a fine-grained bimorphic structure, consisting of fine-sized lamellar clusters and equiaxed γ grains; the lamellar cluster size is 20μm~40μm, the γ grain size is 10μm~20μm, and the γ grain volume fraction is 30%~60%. Alternatively, the alloy has a fine-grained near-lamellar structure, consisting of fine-sized lamellar clusters and fine spherical γ grains dispersed at the lamellar cluster boundaries; the lamellar cluster size is 40μm~80μm; the γ grain diameter is 5μm~10μm, and the γ grain volume fraction is 5%~30%.

[0032] A deformation-based heat treatment method for TiAl alloys includes the following steps:

[0033] Step 1: The TiAl alloy is subjected to hot isostatic pressing (HIP) to obtain a dense TiAl alloy workpiece; TiAl alloy ingots are prepared by induction solidification melting, and the impurity O introduced into the TiAl alloy ingots does not exceed 0.05% by atomic percentage. The TiAl alloy ingots are subjected to HIP at a temperature of 1160℃, a pressure of 140MPa, and a treatment time of 4h.

[0034] Step 2: Hold the alloy workpiece obtained in Step 1 at the upper temperature of the α2+γ phase region for time t1; then compress and deform the alloy workpiece, and after cooling, obtain the pre-deformed and compressed alloy workpiece; wherein the upper temperature of the α2+γ phase region Te–T≤deformation temperature<Te, and Te is the eutectoid temperature of α→α2+γ.

[0035] Pre-deformation treatment was performed using a heat treatment furnace on a universal testing machine. The TiAl alloy billet was placed in a compression fixture within the furnace and fixed, then held at that temperature for 5–20 minutes (t1). The compression deformation was 10%–50% at a rate of 0.05 cm·s. -1 ~0.005cm·s -1 After the deformation process is completed, the pre-deformed and compressed billet is quickly removed from the heat treatment furnace and allowed to cool naturally to room temperature in the air to obtain the pre-deformed and compressed alloy workpiece.

[0036] Step 3: Hold the pre-deformed and compressed alloy workpiece obtained in Step 2 at the upper temperature of the α+γ dual-phase region or the lower temperature of the dual-phase region for t2 time, and after cooling, obtain a fine-grained near-lamellar TiAl alloy or a fine-grained dual-phase structure; perform heat treatment using a box-type resistance furnace.

[0037] The upper section of the α+γ two-phase region has a temperature range of Tα-1 / 2(Tα-Tγ) to Tα, and the lower section of the α+γ two-phase region has a temperature range of Tα-3 / 4(Tα-Tγ) to Tα-1 / 2(Tα-Tγ). Tα is the temperature at the boundary between the α single-phase region and the phase region containing α+γ phases, and Tγ is the lower limit temperature of the phase region containing α+γ phases.

[0038] The t2 treatment time is 10 min to 24 h. After the heat treatment is completed, the alloy workpiece is placed in the air and allowed to cool naturally to room temperature.

[0039] The TiAl alloy in this invention possesses a thermodynamically stable α+γ two-phase region to meet the processing temperature requirements in the specific steps of this invention. The Ti-Al binary phase diagram is shown below. Figure 2 As shown, the specific composition of the TiAl alloy affects the temperature range of the thermodynamically stable α+γ two-phase region of the TiAl alloy. The alloy composition in this invention satisfies... Figure 2 The phase temperature range in the middle.

[0040] Example 1

[0041] A deformation-based heat treatment method for TiAl alloys includes the following steps:

[0042] Step 1: Ti-47Al-2Cr-2Nb alloy ingots were prepared using induction solidification melting (the composition of the alloy could be determined by inductively coupled atomic emission spectrometry). The impurity O introduced into the TiAl alloy ingot did not exceed 0.05% by atomic percentage. The TiAl alloy ingots were then subjected to hot isostatic pressing (HIP) at a temperature of 1160℃ and a pressure of 140MPa for 4 hours.

[0043] Figure 3Image a shows the SEM image of the alloy. It can be seen that its microstructure consists of coarse lamellar clusters, with cluster sizes ranging from 200 to 400 μm, belonging to a coarse-grained, fully lamellar structure. Image b shows the SEM image after hot isostatic pressing. It can be seen that the average size of the lamellar clusters remains unchanged, but the discontinuous coarsened γ-lamellae at the boundaries of the original as-cast microstructure have grown, forming a small number of γ-grains at the cluster boundaries. The average size of these γ-grains is approximately 55 μm.

[0044] Step 2: The heat treatment furnace of the universal testing machine is heated to 900℃. The Ti-47Al-2Cr-2Nb alloy, after hot isostatic pressing, is placed in the heat treatment furnace of the universal testing machine. After holding at this temperature for 20 minutes, it is compressed at a deformation rate of 0.5 mm / s, with a deformation amount of 25%, ensuring the uniformity of the sample temperature during compression and preventing fracture. After compression, the compressed billet is quickly removed from the heat treatment furnace and allowed to cool naturally to room temperature in air to obtain a pre-deformed compressed forging. The microstructure of the alloy after pre-deformation compression is as follows... Figure 3 Figures c and d show the results. Figure c shows significant bending of the lamellar sheets and γ-recrystallization at the boundaries of the lamellar clusters. Figure d shows a high-magnification SEM image of the interior of the lamellar clusters after pre-deformation treatment, revealing twinning within the sheets.

[0045] Step 3: Before isothermal heat treatment, the pre-deformed billet is vacuum-sealed in a high-temperature resistant quartz tube to prevent the TiAl alloy from oxidizing during the heat treatment process.

[0046] After heating the billet to 1280℃ in a box-type resistance furnace, the pre-deformed and compressed billet is transferred into the furnace and held isothermally for 24 hours. After the holding period, the billet is removed and placed in air to cool naturally to room temperature. The resulting product after this heat treatment process is as follows: Figure 4 As shown in Figure a, the average size of its lamellar clusters is 20 μm, the lamellar cluster refinement is more than 10 times, the average size of the equiaxed γ grains is 12 μm, the lamellar cluster content is about 60%, and it belongs to a bimorphic structure.

[0047] After heating the billet to 1320℃ in a box-type resistance furnace, the pre-deformed and compressed billet is transferred into the furnace and held isothermally for 24 hours. After the holding period, the billet is removed and placed in air to cool naturally to room temperature. The resulting product after heat treatment using this process is as follows: Figure 4 The microstructure of b, as shown in the figure, consists of lamellar clusters and fine equiaxed γ grains at the boundaries of the lamellar clusters. The average size of the lamellar clusters is 73 μm, and the average size of the equiaxed γ grains is 10 μm. The refinement of both the lamellar clusters and γ grains is more than 5 times. The lamellar cluster content is about 85%, which belongs to the near-lamellar structure.

[0048] Example 2

[0049] A deformation-based heat treatment method for TiAl alloys includes the following steps:

[0050] Step 1: Ti-47Al-2Cr-2Nb alloy ingots were prepared using induction solidification melting (the composition of the alloy could be determined by inductively coupled atomic emission spectrometry). The impurity O introduced into the TiAl alloy ingot did not exceed 0.05% by atomic percentage. The TiAl alloy ingots were then subjected to hot isostatic pressing (HIP) at a temperature of 1160℃ and a pressure of 140MPa for 4 hours.

[0051] Step 2: The heat treatment furnace of the universal testing machine is heated to 900℃. The Ti-47Al-2Cr-2Nb alloy, after hot isostatic pressing, is placed into the heat treatment furnace of the universal testing machine. After holding at this temperature for 5 minutes, it is compressed at a deformation rate of 0.05 mm / s with a deformation amount of 10%, ensuring the uniformity of the sample temperature during compression and preventing fracture. After compression, the compressed billet is quickly removed from the heat treatment furnace and allowed to cool naturally to room temperature in air to obtain a pre-deformed compressed forging billet.

[0052] Step 3: Before isothermal heat treatment, the pre-deformed billet is vacuum-sealed in a high-temperature resistant quartz tube to prevent the TiAl alloy from oxidizing during the heat treatment process.

[0053] After heating the billet to 1280℃ in a box-type resistance furnace, the pre-deformed and compressed billet is transferred into the furnace and held isothermally for 12 hours. After the holding period, the billet is removed and placed in air to cool naturally to room temperature. This heat treatment process yields a bimodal microstructure.

[0054] After heating the billet to 1320℃ in a box-type resistance furnace, the pre-deformed and compressed billet is transferred into the furnace and held isothermally for 12 hours. After the holding period, the billet is removed and placed in air to cool naturally to room temperature. This heat treatment process yields a near-lamellar microstructure.

[0055] Example 3

[0056] A deformation-based heat treatment method for TiAl alloys includes the following steps:

[0057] Step 1: Ti-47Al-2Cr-2Nb alloy ingots were prepared using induction solidification melting (the composition of the alloy could be determined by inductively coupled atomic emission spectrometry). The impurity O introduced into the TiAl alloy ingot did not exceed 0.05% by atomic percentage. The TiAl alloy ingots were then subjected to hot isostatic pressing (HIP) at a temperature of 1160℃ and a pressure of 140MPa for 4 hours.

[0058] Step 2: The heat treatment furnace of the universal testing machine is heated to 900℃. The Ti-47Al-2Cr-2Nb alloy, after hot isostatic pressing, is placed into the heat treatment furnace of the universal testing machine. After holding at this temperature for 15 minutes, it is compressed at a deformation rate of 0.1 mm / s, with a deformation amount of 50%, ensuring the uniformity of the sample temperature during compression and preventing fracture. After compression, the compressed billet is quickly removed from the heat treatment furnace and allowed to cool naturally to room temperature in air to obtain a pre-deformed compressed forging billet.

[0059] Step 3: Before isothermal heat treatment, the pre-deformed billet is vacuum-sealed in a high-temperature resistant quartz tube to prevent the TiAl alloy from oxidizing during the heat treatment process.

[0060] After heating the billet to 1280℃ in a box-type resistance furnace, the pre-deformed and compressed billet is transferred into the furnace and held isothermally for 10 minutes. After the holding period, the billet is removed and placed in air to cool naturally to room temperature. This heat treatment process yields a bimodal microstructure.

[0061] After heating the billet to 1320℃ in a box-type resistance furnace, the pre-deformed and compressed billet is transferred into the furnace and held isothermally for 10 minutes. After the holding period, the billet is removed and placed in air to cool naturally to room temperature. This heat treatment process yields a near-lamellar microstructure.

[0062] Due to the low room temperature plasticity and poor deformability of TiAl alloys, room temperature processing is generally difficult, and there is currently no research on using low-temperature deformation of TiAl alloys for microstructure refinement. High-temperature deformation is often accompanied by complex phase transformations, altering its phase structure and microstructure. This invention, operating below the phase transformation temperature (γ phase → α phase) and the order-disorder transition temperature (where, upon temperature increase to a specific temperature, the ordered phase α2 transforms into the high-temperature disordered phase α), ensures that the deformation process only results in the accumulation of microstructural defects and partial γ recrystallization, accumulating deformation storage energy and nucleation sites for subsequent heat treatment. Simultaneously, at this deformation temperature, the TiAl alloy has already undergone high-temperature softening, and its plasticity is much higher than its room temperature plasticity. Small deformation compression at this temperature makes the compressed specimen less prone to cracking. Therefore, this deformation method for microstructure control is highly reasonable and feasible. This invention is simple to operate; both the deformation and heat treatment processes are isothermal, requiring no control of the heating and cooling processes. Meanwhile, since each step is independent, and both deformation and heat treatment are isothermal processes and are air-cooled, the next step is carried out only after each step is completed. There is no need to control temperature changes between steps. Therefore, the pre-deformation and isothermal heat treatment of this invention do not require continuity.

Claims

1. A deformation-based heat treatment method for TiAl alloys, characterized in that, Includes the following steps: Step 1: Hot isostatic pressing is applied to the TiAl alloy to obtain a dense TiAl alloy workpiece; Step 2: Hold the alloy workpiece obtained in Step 1 at the upper temperature of the α2+γ phase region for time t1; then compress and deform the alloy workpiece, and after cooling, obtain the pre-deformed and compressed alloy workpiece; wherein the upper temperature of the α2+γ phase region Te –T≤deformation temperature<Te, Te is the eutectoid temperature of α→α2+γ; T is 100~300 ℃. Step 3: Hold the pre-deformed and compressed alloy workpiece obtained in Step 2 at the upper temperature of the α+γ dual-phase region or the lower temperature of the dual-phase region for t2 time, and after cooling, obtain a fine-grained near-lamellar TiAl alloy or a fine-grained dual-phase structure. The upper section of the α+γ two-phase region has a temperature range of Tα-1 / 2(Tα-Tγ) to Tα, while the lower section of the α+γ two-phase region has a temperature range of Tα-3 / 4(Tα-Tγ) to Tα-1 / 2(Tα-Tγ). Here, Tα is the temperature at the boundary between the α single-phase region and the phase region containing both α and γ phases, and Tγ is the lower limit temperature of the phase region containing both α and γ phases. The alloy is: Ti-(43~48)Al-(0~8)X-(0~0.5)Z, wherein X is one or more of Nb, Mo, Cr, Ta, V, and Mn; Z is one or more of Fe, C, N, O, B, and Si; the alloy has a fine-grained bimorphic structure, which consists of fine-sized lamellar clusters and equiaxed γ grains; the lamellar cluster size is 20 μm~40 μm, the γ grain size is 10 μm~20 μm, and the volume fraction of γ grains is 30%~60%. Alternatively, the alloy may have a fine-grained near-lamellar structure, consisting of small-sized lamellar clusters and fine spherical γ grains dispersed on the boundaries of the lamellar clusters; the size of the lamellar clusters is 40 μm to 80 μm; the diameter of the γ grains is 5 μm to 10 μm, and the volume fraction of the γ grains is 5% to 30%.

2. The deformation-based heat treatment method for TiAl alloy according to claim 1, characterized in that, In step 1, the hot isostatic pressing treatment temperature is 1160 ℃, the pressure is 140 MPa, and the treatment time is 4 h.

3. The deformation-based heat treatment method for TiAl alloy according to claim 1, characterized in that, In step 2, the t1 time is 5~20min, and the t2 time is 10min~24h.

4. The deformation-based heat treatment method for TiAl alloy according to claim 1, characterized in that, The cooling in steps 2 and 3 is achieved by air cooling.

5. The deformation-based heat treatment method for TiAl alloy according to claim 1, characterized in that, The compression deformation in step 2 is 10% to 50%.

6. The deformation-based heat treatment method for TiAl alloy according to claim 1, characterized in that, The compression deformation rate in step 2 is 0.05 cm·s. -1 ~0.005 cm·s -1 .

7. The application of TiAl alloys obtained by deformation heat treatment method according to any one of claims 1 to 6, characterized in that, The TiAl alloy is used as a high-temperature structural material.

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