Heat treatment method for improving room-temperature plasticity of TiAl alloy

Abstract

The invention provides a heat treatment method for improving room-temperature plasticity of a TiAl alloy, and relates to the technical field of heat treatment of TiAl alloys. The method comprises the following steps: weighing raw materials according to the atom content ratio of the TiAl alloy; smelting the raw material cloth in a vacuum induction suspension smelting furnace, casting the raw material cloth in a stainless steel mold, and performing furnace cooling to room temperature to obtain an as-cast TiAl alloy ingot; the TiAl alloy cast ingot is subjected to hot isostatic pressing treatment, and a hot isostatic pressing state alloy is obtained; and performing high-temperature heat treatment on the alloy in the hot isostatic pressing state to obtain the TiAl alloy with the near-lamellar structure. According to the TiAl alloy prepared through component design and smelting, after hot isostatic pressing and heat treatment, the lamellar cluster size and lamellar spacing are reduced, and fine lamellar clusters with nano lamellas are obtained in equiaxial gamma crystal grains; the prepared TiAl alloy is high in room temperature strength and good in plasticity, the percentage elongation after fracture can reach 1-1.84%, the subsequent machinability is further improved, and the method is simple and easy to operate, low in cost, short in process, high in efficiency and beneficial to industrial large-scale production and popularization.

Description

Technical Field

[0001] The invention relates to the technical field of heat treatment of TiAl alloy, in particular to a heat treatment method for improving the room temperature plasticity of TiAl alloy. Background Art

[0002] As a new type of lightweight high-temperature structural material, TiAl alloy has the advantages of high melting point, low density, high specific strength, and excellent comprehensive mechanical properties. The theoretical density of TiAl alloy is about half of that of nickel-based high-temperature alloy, only 3.9-4.2g / cm 3 , is an ideal material for engine weight reduction design in the aerospace field.

[0003] TiAl alloys have four typical microstructures: near-gamma (NG), duplex, near-lamellar (NL), and fully lamellar (FL). According to the Hall-Petch relationship, a gradual reduction in grain size improves the alloy's strength and ductility. Therefore, fine, uniform fully lamellar or near-lamellar microstructures are ideal for this alloy.

[0004] Currently, typical materials used for blades in the aviation field include cast 4822 alloy and forged TNM alloy. Industrially, TiAl alloys are primarily produced through casting, which is the most economical method. However, cast TiAl alloys suffer from problems such as coarse microstructure, component segregation, and casting defects, which in turn reduce the mechanical properties of TiAl alloys. Therefore, while retaining the low-cost production advantages of casting, improving the room temperature and high-temperature mechanical properties of cast TiAl alloys and obtaining alloy compositions and preparation processes with excellent comprehensive mechanical properties are the key areas of development and research for this alloy system.

[0005] Heat treatment is an effective method to improve the microstructure and mechanical properties of TiAl alloys. Studies have shown that hot isostatic pressing can eliminate casting defects and reduce composition segregation in cast TiAl alloys. High-temperature heat treatment after hot isostatic pressing can further adjust the microstructure of TiAl alloys, refine the grain size and interlamellar spacing, and thus improve the mechanical properties of TiAl alloys.

[0006] Chinese patent CN105220096A discloses a multi-step cyclic heat treatment method for improving the mechanical properties of conventional cast γ-TiAl alloys. This method effectively improves the room-temperature properties of the γ-TiAl alloy by continuously cyclically heat treating the homogenized TiAl alloy in the α+γ two-phase region. However, this method requires a large amount of time or multiple repeated treatments and is relatively costly.

[0007] Chinese patent CN118241138A discloses a method for multi-physics collaborative processing to modify the room temperature elongation of cast TiAl4822 alloy. The method improves the room temperature elongation of the alloy after multi-physics field combined heat treatment. However, the alloy strength is low and the entire production process is too long. A large number of equipment is required, which is difficult to meet engineering applications. It also does not improve the composition of the TiAl alloy from the source.

[0008] Chinese patent CN112746232A discloses a method for improving the strength and plasticity of β-type γ-TiAl alloy. This method improves the strength and plasticity by hot isostatic pressing the TiAl alloy cast rod, removing the surface oxide layer, hot extruding after jacketing, and removing the jacket after annealing. Therefore, the heat treatment and machining process are complicated, the operation is difficult, the production cost is high, and it is not suitable for industrial production.

[0009] Chinese patent CN108385046A discloses a heat treatment method for a TiAl-V alloy, which includes solution treatment, cooling, and tempering steps. The microstructure of the prepared alloy is a cast microstructure with low density. The microstructure and the gaps therebetween are larger than the microstructure size after hot isostatic pressing. The room temperature strength and plasticity of the material after hot isostatic pressing are not effectively adjusted by selecting the alloy composition.

[0010] Therefore, improving the heat treatment process of TiAl alloy to obtain excellent comprehensive mechanical properties, especially taking into account the room temperature strength and plasticity, is crucial for the engineering application of TiAl alloy, especially a new refinement method that is suitable for industrial application, simple, easy and low-cost. Summary of the Invention

[0011] In order to solve the technical problems in the existing technology of TiAl alloy preparation that cannot balance room temperature strength and plasticity, and that heat treatment and machining can improve strength and plasticity, but the process is complicated, the operation is difficult, the production cost is high, the efficiency is low, and it is not conducive to industrial production, and the prepared alloy material has a coarse structure and large interlamellar spacing; the present invention proposes a heat treatment method for improving the room temperature plasticity of TiAl alloy that can solve all the above technical problems. The technical solution is as follows:

[0012] A heat treatment method for improving the room temperature plasticity of a TiAl alloy comprises the following steps:

[0013] S1. Raw material weighing: weigh the raw materials according to the atomic content ratio of the chemical composition of TiAl alloy;

[0014] S2. Vacuum melting and casting: The raw material weighed in S1 is melted in a copper crucible of a vacuum induction levitation melting furnace, and then cast into a stainless steel mold and cooled to room temperature with the furnace to obtain a cast TiAl alloy ingot;

[0015] S3, hot isostatic pressing: hot isostatic pressing the S2 cast TiAl alloy ingot to obtain a hot isostatically pressed alloy;

[0016] S4. High temperature heat treatment: The S3 hot isostatically pressed alloy is subjected to high temperature heat treatment to obtain a TiAl alloy with a near lamellar structure.

[0017] Optionally, the chemical composition atomic content ratio of the TiAl alloy in S1 is: Al 46-50at%, Nb 1-4at%, Cr1-4at%, Si 0-0.4at%, and the balance is Ti and unavoidable impurity elements.

[0018] Optionally, the raw materials in S1 include pure metal sponge titanium with a purity of 99.99%, aluminum ingot, chromium powder, silicon powder, and aluminum-niobium master alloy with a niobium mass fraction of 73.2%.

[0019] Optionally, when the melting power in S2 is 100-120W, the alloy is kept for 5 minutes after being completely melted to allow the molten alloy liquid to fully mix and react; in addition, the melting needs to be repeated 2-3 times to obtain a TiAl alloy ingot with uniform composition; this step can heal casting shrinkage and some shrinkage cavities, improve density, and promote tissue evolution.

[0020] Optionally, the hot isostatic pressing process parameters in S3 are as follows: temperature controlled within the range of 1200-1330° C., pressure of 150-200 MPa, holding time of 2-10 h, and furnace cooling.

[0021] Optionally, the microstructure of the hot isostatically pressed alloy in S3 is a dual-state microstructure consisting of lamellar clusters and equiaxed γ grains.

[0022] Optionally, the high temperature heat treatment in S4 is carried out in a muffle furnace, and the process parameters are temperature control in the range of 1250-1360°C, heating rate of 10-20°C / min, holding time of 0-10h, and air cooling.

[0023] Optionally, the TiAl alloy with near-lamellar structure in S4 is composed of fine lamellar clusters, equiaxed γ grains and extremely fine lamellar clusters with nano-lamellar layers within the equiaxed γ grains; the extremely fine lamellar clusters within the equiaxed γ grains are only 5-20 μm in size, and the lamellar spacing is 5-60 nm; the α2 phase content is 5-15%, and the γ phase content is 85-95%.

[0024] Alternatively, the mechanical properties of the TiAl alloy with near lamellar structure in S4 were tested, and the room temperature tensile rate was 1.0×10 ‐4 s ‐1The tensile strength is 600-660MPa, the yield strength is 430-490MPa, the elongation after fracture is 1.0-1.8%, and the room temperature plasticity is increased by 60-90% compared with the cast state.

[0025] Optionally, the TiAl alloy composition of the lamellar structure in S4 is Ti-47Al-2Cr-2Nb-0.2Si, and the alloy of this composition is subjected to hot isostatic pressing at a temperature of 1310°C, a pressure of 150 MPa, and a time of 4 hours, followed by furnace cooling; the alloy of this composition after hot isostatic pressing is subjected to high-temperature heat treatment at a temperature of 1310°C, a time of 4 hours, and air cooling; a room temperature tensile test is performed at a tensile rate of 1.0×10 ‐4 s ‐1 The room temperature tensile results show that the tensile strength of Ti-47Al-2Cr-2Nb-0.2Si alloy is 644MPa, the elongation after fracture is 1.84%, and the room temperature plasticity is improved by 90% compared with the cast state.

[0026] The technical principle of the present invention is as follows: hot isostatic pressing is used to eliminate casting defects, improve density, and reduce the dispersion of mechanical properties; under an optimized heat treatment process, a fine and uniform microstructure is obtained by controlling the heat treatment temperature, holding time, and cooling rate, and phase transformation is used to obtain extremely fine lamellar clusters with nanosheet layers within equiaxed γ grains, greatly improving room temperature plasticity.

[0027] Compared with the prior art, the above technical solution has at least the following beneficial effects:

[0028] The above scheme, the present invention proposes a heat treatment method for improving the room temperature plasticity of TiAl alloy, which can solve the technical problems in the existing technology that the preparation of TiAl alloy cannot take into account both room temperature strength and plasticity, and there are problems such as heat treatment and machining that can improve strength and plasticity but the process is complicated, the operation is difficult, the production cost is high, the efficiency is low, and it is not conducive to industrial production, and the prepared alloy material has coarse structure and large lamellar cluster spacing.

[0029] The present invention eliminates casting defects by hot isostatic pressing of TiAl alloy, and well controls the organizational evolution through subsequent heat treatment to obtain a near-lamellar structure consisting of fine lamellar clusters, equiaxed γ grains and very fine lamellar clusters with nano-lamellae within the equiaxed γ grains.

[0030] The present invention effectively improves the room temperature performance of the cast TiAl alloy through simple heat treatment. After the heat treatment method of the present invention, the room temperature tensile strength of the TiAl alloy is 600-660 MPa, and the elongation after fracture is 1.4-1.8%.

[0031] The present invention improves the composition of the TiAl alloy from the source and combines hot isostatic pressing and high-temperature heat treatment to refine the microstructure, synergistically improve the room-temperature plasticity and strength, and facilitate subsequent processing, thereby expanding the application range of the TiAl alloy and having a high degree of commercialization.

[0032] The present invention has simple and efficient operation, a simple process, a short cycle, and low production cost, and can be used as an effective means to effectively improve the strength and plasticity of TiAl alloys.

[0033] In summary, compared with other traditional methods, the method of the present invention improves the room temperature strength and plasticity of TiAl alloy through composition design, multiple smelting, hot isostatic pressing and high-temperature heat treatment; the prepared TiAl alloy has good room temperature tensile strength and elongation after fracture, and excellent strength and plasticity, further improving the subsequent machinability of the prepared TiAl alloy, greatly broadening the commercial prospects of TiAl alloy. The method is simple and easy to operate, low cost, short process and high efficiency, which is conducive to large-scale industrial production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 This is a cast microstructure diagram of a TiAl alloy ingot prepared by a heat treatment method for improving the room temperature plasticity of a TiAl alloy according to Example 1 of the present invention;

[0036] Figure 2 This is a microstructure diagram of a TiAl alloy after hot isostatic pressing and heat treatment, prepared by a heat treatment method for improving the room temperature plasticity of a TiAl alloy according to Example 1 of the present invention;

[0037] Figure 3 This is a microstructure diagram of a TiAl alloy after hot isostatic pressing and heat treatment, prepared by a heat treatment method for improving the room temperature plasticity of a TiAl alloy according to Example 2 of the present invention;

[0038] Figure 4 This is a comparison diagram of room temperature tensile curves of the cast and heat-treated TiAl alloys prepared by a heat treatment method for improving the room temperature plasticity of TiAl alloys in Example 1 of the present invention. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0040] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as an "exemplary" in the present invention should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of the word "exemplary" is intended to present concepts in a concrete manner. Furthermore, in the embodiments of the present invention, "and / or" can mean both or either of the two.

[0041] In the embodiments of the present invention, “image” and “picture” may sometimes be used interchangeably. It should be noted that when the distinction between them is not emphasized, the meanings they intend to express are the same.

[0042] In the embodiments of the present invention, sometimes a subscript such as W1 may be written as a non-subscript such as W1. When the difference is not emphasized, the meanings to be expressed are the same.

[0043] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0044] A heat treatment method for improving the room temperature plasticity of a TiAl alloy comprises the following steps:

[0045] S1. Raw material weighing: weigh the raw materials according to the atomic content ratio of the chemical composition of TiAl alloy;

[0046] S2. Vacuum melting and casting: The raw material weighed in S1 is melted in a copper crucible of a vacuum induction levitation melting furnace, and then cast into a stainless steel mold and cooled to room temperature with the furnace to obtain a cast TiAl alloy ingot;

[0047] S3, hot isostatic pressing: hot isostatic pressing the S2 cast TiAl alloy ingot to obtain a hot isostatically pressed alloy;

[0048] S4. High temperature heat treatment: The S3 hot isostatically pressed alloy is subjected to high temperature heat treatment to obtain a TiAl alloy with a near lamellar structure.

[0049] In particular, the chemical composition atomic ratio of the TiAl alloy in S1 is: Al 46-50at%, Nb 1-4at%, Cr1-4at%, Si 0-0.4at%, and the balance is Ti and unavoidable impurity elements.

[0050] In particular, the raw materials in S1 are pure metal sponge titanium with a purity of 99.99%, aluminum ingots, chromium powder, silicon powder, and aluminum-niobium master alloy with a niobium mass fraction of 73.2%.

[0051] In particular, when the melting power in S2 is 100-120W, the alloy is kept for 5 minutes after being completely melted to allow the molten alloy liquid to fully mix and react; in addition, the melting needs to be repeated 2-3 times to obtain a TiAl alloy ingot with uniform composition; this step can heal casting shrinkage and some shrinkage cavities, improve density, and promote organizational evolution.

[0052] In particular, the hot isostatic pressing process parameters in S3 are temperature controlled in the range of 1200-1330°C, pressure of 150-200 MPa, holding time of 2-10 h, and furnace cooling.

[0053] In particular, the microstructure of the hot isostatically pressed alloy in S3 is a dual-state microstructure consisting of lamellar clusters and equiaxed γ grains.

[0054] In particular, the high-temperature heat treatment of S4 was carried out in a muffle furnace, and the process parameters were temperature control in the range of 1250-1360 °C, heating rate of 10-20 °C / min, holding time of 0-10 h, and air cooling.

[0055] In particular, the TiAl alloy with near-lamellar structure in S4 is composed of fine lamellar clusters, equiaxed γ grains and extremely fine lamellar clusters with nano-lamellar layers within the equiaxed γ grains; the extremely fine lamellar clusters within the equiaxed γ grains are only 5-20μm in size, and the interlamellar spacing is 5-60nm; the α2 phase content is 5-15%, and the γ phase content is 85-95%.

[0056] In particular, the mechanical properties of the TiAl alloy with near lamellar structure in S4 were tested, and the room temperature tensile rate was 1.0×10 ‐4 s ‐1 The tensile strength is 600-660MPa, the yield strength is 430-490MPa, the elongation after fracture is 1.0-1.8%, and the room temperature plasticity is increased by 60-90% compared with the cast state.

[0057] In particular, the composition of the TiAl alloy with lamellar structure in S4 is Ti-47Al-2Cr-2Nb-0.2Si. The alloy was subjected to hot isostatic pressing at a temperature of 1310°C, a pressure of 150 MPa, and a time of 4 h, followed by furnace cooling. The alloy after hot isostatic pressing was subjected to high-temperature heat treatment at a temperature of 1310°C, a time of 4 h, and air cooling. A room temperature tensile test was performed at a tensile rate of 1.0×10 ‐4 s ‐1 The room temperature tensile results show that the tensile strength of Ti-47Al-2Cr-2Nb-0.2Si alloy is 644MPa, the elongation after fracture is 1.84%, and the room temperature plasticity is improved by 90% compared with the cast state.

[0058] Example 1

[0059] A heat treatment method for improving the room temperature plasticity of a TiAl alloy, wherein the TiAl alloy is Ti-47Al-2Cr-2Nb-0.2Si, and the heat treatment method for improving the room temperature plasticity of the TiAl alloy comprises the following steps:

[0060] S1. Raw material weighing: weigh the raw materials according to the atomic content ratio of the chemical composition of the TiAl alloy; the raw materials used are pure metal sponge titanium with a purity of 99.99%, high-purity aluminum ingot, chromium powder, silicon powder, and aluminum-niobium master alloy with a niobium mass fraction of 73.2%;

[0061] S2, vacuum melting and casting: The raw material weighed in S1 is melted in a copper crucible of a vacuum induction suspension melting furnace. When the melting power is 100-120W, the alloy is completely melted and kept for 5 minutes to allow the molten alloy liquid to fully mix and react. The melting needs to be repeated twice to obtain a TiAl alloy ingot with uniform composition. The ingot is then cast into a stainless steel mold and cooled to room temperature with the furnace to obtain a cast TiAl alloy ingot. Figure 1 As shown in the figure, the as-cast TiAl alloy is a nearly full lamellar structure with a lamellar cluster size of 200 μm. 19 It is composed of Ti3Al (α2) phase with L10 structure and TiAl (γ) phase with L10 structure, with the volume fraction of α2 phase being 15% and the volume fraction of γ phase being 85%.

[0062] S3. Hot isostatic pressing: The S2 cast TiAl alloy ingot was subjected to hot isostatic pressing. The hot isostatic pressing process parameters were as follows: temperature controlled at 1310°C, pressure of 150 MPa, holding time of 4 h, and furnace cooling to obtain a hot isostatically pressed alloy. The hot isostatically pressed alloy had a dual-state structure, a grain size of 190 μm, and a phase structure of α2 phase and γ phase. The volume fraction of α2 phase was 7%, and the volume fraction of γ phase was 93%.

[0063] S4. High temperature heat treatment: The S3 hot isostatically pressed alloy was subjected to high temperature heat treatment in a muffle furnace. The process parameters were as follows: temperature controlled at 1310°C, heating rate of 20°C / min, holding time of 4h, and air cooling to obtain a TiAl alloy with a near lamellar structure.

[0064] like Figure 2 As shown in the figure, the near-lamellar structure prepared in this embodiment has an average grain size of 144 μm, and is composed of fine lamellar clusters, equiaxed γ grains and extremely fine lamellar clusters with nano-sheet layers within the equiaxed γ grains; the extremely fine lamellar clusters within the equiaxed γ grains are only 10 μm in size, and the lamellar spacing is 50 nm; the α2 phase content is 9%, and the γ phase content is 91%.

[0065] The mechanical properties of the TiAl alloy with near lamellar structure prepared in this example were tested. The tensile rate at room temperature was 1.0×10 ‐4 s‐1 ,like Figure 4 As shown, the tensile strength is 634 MPa, the yield strength is 550 MPa, the elongation after fracture is 1.8%, the strength-ductility product is 1.141 GPa·%, and the room temperature plasticity is improved by 90% compared with the cast state.

[0066] Example 2

[0067] A heat treatment method for improving the room temperature plasticity of a TiAl alloy, wherein the TiAl alloy is Ti-47Al-2Cr-2Nb, and the heat treatment method for improving the room temperature plasticity of the TiAl alloy comprises the following steps:

[0068] S1. Raw material weighing: weigh the raw materials according to the atomic content ratio of the chemical composition of the TiAl alloy; the raw materials used are pure metal sponge titanium with a purity of 99.99%, high-purity aluminum ingots, chromium powder, and aluminum-niobium master alloy with a niobium mass fraction of 73.2%;

[0069] S2, vacuum melting and casting: The raw material weighed in S1 is melted in a copper crucible of a vacuum induction suspension melting furnace. When the melting power is 100-120W, the alloy is completely melted and kept for 5 minutes to allow the molten alloy liquid to fully mix and react. The melting needs to be repeated twice to obtain a TiAl alloy ingot with uniform composition. The ingot is then cast into a stainless steel mold and cooled to room temperature with the furnace to obtain a cast TiAl alloy ingot. Figure 3 As shown in the figure, the as-cast TiAl alloy is nearly fully lamellar, with a lamellar cluster size of 210 μm. 19 It is composed of Ti3Al (α2) phase with L10 structure and TiAl (γ) phase with L10 structure, with the volume fraction of α2 phase being 14% and the volume fraction of γ phase being 86%.

[0070] S3. Hot isostatic pressing: The S2 cast TiAl alloy ingot was subjected to hot isostatic pressing. The hot isostatic pressing process parameters were as follows: temperature controlled at 1310°C, pressure at 150 MPa, holding time at temperature and pressure for 4 hours, and furnace cooling to obtain a hot isostatically pressed alloy. The hot isostatically pressed alloy had a dual-state structure, a grain size of 230 μm, and a phase structure of α2 phase and γ phase. The volume fraction of α2 phase was 8%, and the volume fraction of γ phase was 92%.

[0071] S4. High temperature heat treatment: The S3 hot isostatically pressed alloy was subjected to high temperature heat treatment in a muffle furnace. The process parameters were as follows: temperature controlled at 1310°C, heating rate of 20°C / min, holding time of 4h, and air cooling to obtain a TiAl alloy with a near lamellar structure.

[0072] The TiAl alloy with a near-lamellar structure prepared in this example consists of fine lamellar clusters, equiaxed γ grains, and extremely fine lamellar clusters with nano-lamellar layers within the equiaxed γ grains; the extremely fine lamellar clusters within the equiaxed γ grains are only 15 μm in size, and the lamellar spacing is 60 nm; the α2 phase content is 9%, and the γ phase content is 91%.

[0073] The mechanical properties of the TiAl alloy with near lamellar structure prepared in this example were tested. The tensile rate at room temperature was 1.0×10 ‐4 s ‐1 The tensile strength is 647MPa, the yield strength is 494MPa, the elongation after fracture is 1.47%, the strength-ductility product is 0.951GPa·%, and the room temperature plasticity is increased by 64.5% compared with the cast state.

[0074] From the comparison between Example 1 and Example 2, it can be seen that the composition of Example 1 has 0.2% more Si, the tensile strength of the two is similar, the yield strength and elongation after fracture are improved, and the overall strength-ductility product is improved.

[0075] Example 3

[0076] A heat treatment method for improving the room temperature plasticity of a TiAl alloy, wherein the TiAl alloy is Ti-48Al-2Cr-2Nb-0.2Si, and the heat treatment method for improving the room temperature plasticity of the TiAl alloy comprises the following steps:

[0077] S1. Raw material weighing: weigh the raw materials according to the atomic content ratio of the chemical composition of the TiAl alloy; the raw materials used are pure metal sponge titanium with a purity of 99.99%, aluminum ingot, chromium powder, silicon powder, and aluminum-niobium master alloy with a niobium mass fraction of 73.2%;

[0078] S2. Vacuum melting and casting: The raw materials weighed in S1 are melted in a copper crucible of a vacuum induction levitation melting furnace. When the melting power is 100-120W, the alloy is completely melted and kept for 5 minutes to allow the molten alloy liquid to fully mix and react. The melting needs to be repeated twice to obtain a TiAl alloy ingot with uniform composition. The ingot is then cast into a stainless steel mold and cooled to room temperature with the furnace to obtain a cast TiAl alloy ingot. The cast TiAl alloy has a nearly fully lamellar structure with a lamellar cluster size of 250μm. At room temperature, it consists of an ordered D0 19 It is composed of Ti3Al (α2) phase with L10 structure and TiAl (γ) phase with L10 structure, with the volume fraction of α2 phase being 13% and the volume fraction of γ phase being 87%.

[0079] S3. Hot Isostatic Pressing: The S2 cast TiAl alloy ingot was hot isostatically pressed (HIP) using the following process parameters: temperature controlled within 1280°C, pressure of 170 MPa, holding time of 4 hours, and furnace cooling to obtain a HIP alloy. The HIP alloy exhibited a dual-phase structure with a grain size of 230 μm and a phase structure of α2 and γ phases. The volume fraction of the α2 phase was 7%, and the volume fraction of the γ phase was 93%. S4. High-Temperature Heat Treatment: The S3 HIP alloy was subjected to high-temperature heat treatment in a muffle furnace using the following process parameters: temperature controlled within 1330°C, heating rate of 10°C / min, holding time of 10 hours, and air cooling to obtain a TiAl alloy with a near-lamellar structure.

[0080] The TiAl alloy with a near-lamellar structure prepared in this embodiment consists of fine lamellar clusters, equiaxed γ grains, and extremely fine lamellar clusters with nano-lamellar layers within the equiaxed γ grains; the extremely fine lamellar clusters within the equiaxed γ grains are only 30 μm in size, and the lamellar spacing is 50 nm; the α2 phase content is 10%, and the γ phase content is 90%.

[0081] The mechanical properties of the TiAl alloy with near lamellar structure prepared in this example were tested. The tensile rate at room temperature was 1.0×10 ‐4 s ‐1 The tensile strength is 630MPa, the yield strength is 539MPa, the elongation after fracture is 1.3%, the strength-ductility product is 0.819GPa·%, and the room temperature plasticity is increased by 70% compared with the cast state.

[0082] Example 4

[0083] A heat treatment method for improving the room temperature plasticity of a TiAl alloy, wherein the TiAl alloy is Ti-48Al-2Cr-2Nb-0.4Si, and the heat treatment method for improving the room temperature plasticity of the TiAl alloy comprises the following steps:

[0084] S1. Raw material weighing: weigh the raw materials according to the atomic content ratio of the chemical composition of the TiAl alloy; the raw materials used are pure metal sponge titanium with a purity of 99.99%, aluminum ingot, chromium powder, silicon powder, and aluminum-niobium master alloy with a niobium mass fraction of 73.2%;

[0085] S2. Vacuum melting and casting: The raw materials weighed in S1 are melted in a copper crucible of a vacuum induction levitation melting furnace. When the melting power is 100-120W, the alloy is completely melted and kept for 5 minutes to allow the molten alloy liquid to fully mix and react. The melting is repeated 3 times to obtain a TiAl alloy ingot with uniform composition. The ingot is then cast into a stainless steel mold and cooled to room temperature with the furnace to obtain a cast TiAl alloy ingot. The cast TiAl alloy has a nearly fully lamellar structure with a lamellar cluster size of 210μm. At room temperature, it consists of ordered D0 19It is composed of Ti3Al (α2) phase with L10 structure and TiAl (γ) phase with L10 structure, with the volume fraction of α2 phase being 14% and the volume fraction of γ phase being 86%.

[0086] S3. Hot isostatic pressing: The S2 cast TiAl alloy ingot was subjected to hot isostatic pressing. The hot isostatic pressing process parameters were as follows: temperature controlled at 1310°C, pressure at 150 MPa, holding time at temperature and pressure for 4 hours, and furnace cooling to obtain a hot isostatically pressed alloy. The hot isostatically pressed alloy had a dual-state structure, a grain size of 230 μm, and a phase structure of α2 phase and γ phase. The volume fraction of α2 phase was 8%, and the volume fraction of γ phase was 92%.

[0087] S4. High temperature heat treatment: The S3 hot isostatically pressed alloy was subjected to high temperature heat treatment in a muffle furnace. The process parameters were as follows: temperature controlled at 1310°C, heating rate of 10°C / min, holding time of 4h, and air cooling to obtain a TiAl alloy with a near lamellar structure.

[0088] The TiAl alloy with a near-lamellar structure prepared in this embodiment consists of fine lamellar clusters, equiaxed γ grains, and extremely fine lamellar clusters with nano-lamellar layers within the equiaxed γ grains; the extremely fine lamellar clusters within the equiaxed γ grains are only 10 μm in size, and the interlamellar spacing is 60 nm; the α2 phase content is 11%, and the γ phase content is 90%.

[0089] The mechanical properties of the TiAl alloy with near lamellar structure prepared in this example were tested. The tensile rate at room temperature was 1.0×10 ‐4 s ‐1 The tensile strength is 600MPa, the yield strength is 497MPa, the elongation after fracture is 1.0%, the strength-ductility product is 0.6GPa·%, and the room temperature plasticity is increased by 60% compared with the cast state.

[0090] Example 5

[0091] A heat treatment method for improving the room temperature plasticity of a TiAl alloy, wherein the TiAl alloy is Ti-48Al-2Cr-2Nb, and the heat treatment method for improving the room temperature plasticity of the TiAl alloy comprises the following steps:

[0092] S1. Raw material weighing: weigh the raw materials according to the atomic content ratio of the chemical composition of the TiAl alloy; the raw materials used are pure metal sponge titanium, aluminum ingots, chromium powder with a purity of 99.99%, and aluminum-niobium master alloy with a niobium mass fraction of 73.2%;

[0093] S2. Vacuum melting and casting: The raw materials weighed in S1 are melted in a copper crucible of a vacuum induction levitation melting furnace. When the melting power is 100-120W, the alloy is completely melted and kept for 5 minutes to allow the molten alloy liquid to fully mix and react. The melting needs to be repeated twice to obtain a TiAl alloy ingot with uniform composition. The ingot is then cast into a stainless steel mold and cooled to room temperature with the furnace to obtain a cast TiAl alloy ingot. The cast TiAl alloy has a nearly fully lamellar structure with a lamellar cluster size of 240μm. At room temperature, it consists of ordered D0 19 It is composed of Ti3Al (α2) phase with L10 structure and TiAl (γ) phase with L10 structure, with the volume fraction of α2 phase being 12% and the volume fraction of γ phase being 88%.

[0094] S3. Hot Isostatic Pressing: The S2 cast TiAl alloy ingot was hot isostatically pressed (HIP) using the following process parameters: temperature controlled within 1310°C, pressure of 150 MPa, holding time of 4 hours, and furnace cooling to obtain a HIP alloy. The HIP alloy exhibited a dual-phase structure with a grain size of 200 μm and a phase structure of α2 and γ phases. The volume fraction of the α2 phase was 7%, and the volume fraction of the γ phase was 93%. S4. High-Temperature Heat Treatment: The S3 HIP alloy was subjected to high-temperature heat treatment in a muffle furnace using the following process parameters: temperature controlled within 1310°C, heating rate of 20°C / min, holding time of 4 hours, and air cooling to obtain a TiAl alloy with a near-lamellar structure.

[0095] The TiAl alloy with a near-lamellar structure prepared in this example consists of fine lamellar clusters, equiaxed γ grains, and extremely fine lamellar clusters with nano-lamellar layers within the equiaxed γ grains; the extremely fine lamellar clusters within the equiaxed γ grains are only 20 μm in size, and the lamellar spacing is 55 nm; the α2 phase content is 9%, and the γ phase content is 91%.

[0096] The mechanical properties of the TiAl alloy with near lamellar structure prepared in this example were tested. The tensile rate at room temperature was 1.0×10 ‐4 s ‐1 The tensile strength is 632MPa, the yield strength is 485MPa, the elongation after fracture is 1.1%, the strength-ductility product is 0.695GPa·%, and the room temperature plasticity is increased by 61% compared with the cast state.

[0097] Example 6

[0098] A heat treatment method for improving the room temperature plasticity of a TiAl alloy, wherein the TiAl alloy is Ti-47Al-2Cr-3Nb-0.2Si, and the heat treatment method for improving the room temperature plasticity of the TiAl alloy comprises the following steps:

[0099] S1. Raw material weighing: weigh the raw materials according to the atomic content ratio of the chemical composition of the TiAl alloy; the raw materials used are pure metal sponge titanium with a purity of 99.99%, aluminum ingot, chromium powder, silicon powder, and aluminum-niobium master alloy with a niobium mass fraction of 73.2%;

[0100] S2. Vacuum melting and casting: The raw materials weighed in S1 are melted in a copper crucible of a vacuum induction suspension melting furnace. When the melting power is 100-120W, the alloy is completely melted and kept for 5 minutes to allow the molten alloy liquid to fully mix and react. The melting is repeated 3 times to obtain a TiAl alloy ingot with uniform composition. The ingot is then cast into a stainless steel mold and cooled to room temperature with the furnace to obtain a cast TiAl alloy ingot. The cast TiAl alloy has a nearly fully lamellar structure with a lamellar cluster size of 220μm. At room temperature, it consists of ordered D0 19 It is composed of Ti3Al (α2) phase with L10 structure and TiAl (γ) phase with L10 structure, with the volume fraction of α2 phase being 15% and the volume fraction of γ phase being 85%.

[0101] S3. Hot Isostatic Pressing: The S2 cast TiAl alloy ingot was hot isostatically pressed (HIP) using the following process parameters: temperature controlled within 1250°C, pressure of 170 MPa, holding time of 4 hours, and furnace cooling to obtain a HIP alloy. The HIP alloy exhibited a dual-phase structure with a grain size of 200 μm and a phase structure of α2 and γ phases, with a volume fraction of 10% for the α2 phase and 90% for the γ phase. S4. High-Temperature Heat Treatment: The S3 HIP alloy was subjected to high-temperature heat treatment in a muffle furnace using the following process parameters: temperature controlled within 1320°C, heating rate of 20°C / min, holding time of 2 hours, and air cooling to obtain a TiAl alloy with a near-lamellar structure.

[0102] The TiAl alloy with a near-lamellar structure prepared in this example consists of fine lamellar clusters, equiaxed γ grains, and extremely fine lamellar clusters with nano-lamellar layers within the equiaxed γ grains; the extremely fine lamellar clusters within the equiaxed γ grains are only 10 μm in size, and the lamellar spacing is 60 nm; the α2 phase content is 11%, and the γ phase content is 89%.

[0103] The mechanical properties of the TiAl alloy with near lamellar structure prepared in this example were tested. The tensile rate at room temperature was 1.0×10 ‐4 s ‐1 The tensile strength is 640MPa, the yield strength is 500MPa, the elongation after fracture is 1.6%, the strength-ductility product is 1.024GPa·%, and the room temperature plasticity is increased by 63% compared with the cast state.

[0104] Comparative Example 1

[0105] The same preparation method as in Example 1 was used to prepare a Ti-47Al-2Cr-2Nb cast alloy. The same hot isostatic pressing process as in Example 1 was then used to obtain a hot isostatically pressed alloy. The difference was in the heat treatment process, which is as follows:

[0106] High temperature heat treatment: The S3 hot isostatically pressed alloy was subjected to high temperature heat treatment in a muffle furnace. The process parameters were temperature control at 1360°C, heating rate of 20°C / min, holding time of 0.1h, and air cooling to obtain a TiAl alloy with full lamellar structure.

[0107] The TiAl alloy with full lamellar structure prepared in this embodiment has a lamellar cluster size of 400 μm, an α2 phase content of 15%, and a γ phase content of 85%.

[0108] The mechanical properties of the TiAl alloy with near lamellar structure prepared in this example were tested. The tensile rate at room temperature was 1.0×10 ‐4 s ‐1 The tensile strength is 636MPa, the yield strength is 574MPa, the elongation after fracture is 0.37%, the strength-ductility product is 0.235GPa·%, and the plasticity at room temperature is lower than that of the cast state.

[0109] Compared with Comparative Example 1, Example 1 of the present application has a reduced grain size, an increased γ phase content, and after heat treatment, an extremely fine lamellar structure is obtained in the equiaxed γ grains, which has a nano-scale lamellar spacing. Therefore, while maintaining high room temperature strength, the room temperature plasticity is significantly improved; while in Comparative Example 1, the lamellar cluster size is as high as 400 μm, and the room temperature plasticity is only 0.37%.

[0110] A comparison of Examples 1-6 shows that, for alloys within this composition range, hot isostatic pressing can eliminate casting defects, increase density, and reduce the dispersion of tensile data; subsequent heat treatment further regulates the microstructure, refines the grains, and obtains extremely fine lamellar clusters with nanosheets, significantly improving room temperature plasticity.

[0111] The above scheme, the present invention proposes a heat treatment method for improving the room temperature plasticity of TiAl alloy, which can solve the technical problems in the existing technology that the preparation of TiAl alloy cannot take into account both room temperature strength and plasticity, and there are problems such as heat treatment and machining that can improve strength and plasticity but the process is complicated, the operation is difficult, the production cost is high, the efficiency is low, and it is not conducive to industrial production, and the prepared alloy material has coarse structure and large lamellar cluster spacing.

[0112] The present invention eliminates casting defects by hot isostatic pressing of TiAl alloy, and well controls the organizational evolution through subsequent heat treatment to obtain a near-lamellar structure consisting of fine lamellar clusters, equiaxed γ grains and very fine lamellar clusters with nano-lamellae within the equiaxed γ grains.

[0113] The present invention effectively improves the room temperature performance of the cast TiAl alloy through simple heat treatment. After the heat treatment method of the present invention, the room temperature tensile strength of the TiAl alloy is 600-660 MPa, and the elongation after fracture is 1.4-1.8%.

[0114] The present invention improves the composition of the TiAl alloy from the source and combines hot isostatic pressing and high-temperature heat treatment to refine the microstructure, synergistically improve the room-temperature plasticity and strength, and facilitate subsequent processing, thereby expanding the application range of the TiAl alloy and having a high degree of commercialization.

[0115] The present invention has simple and efficient operation, a simple process, a short cycle, and low production cost, and can be used as an effective means to effectively improve the strength and plasticity of TiAl alloys.

[0116] In summary, compared with other traditional methods, the method of the present invention improves the room temperature strength and plasticity of TiAl alloy through composition design, multiple smelting, hot isostatic pressing and high-temperature heat treatment; the prepared TiAl alloy has good room temperature tensile strength and elongation after fracture, and excellent strength and plasticity, further improving the subsequent machinability of the prepared TiAl alloy, greatly broadening the commercial prospects of TiAl alloy. The method is simple and easy to operate, low cost, short process and high efficiency, which is conducive to large-scale industrial production and promotion.

[0117] It should be understood that the term "and / or" as used herein simply describes a relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A alone, A and B together, or B alone. A and B can be singular or plural. Furthermore, the character " / " as used herein generally indicates an "or" relationship between the associated objects, but it may also indicate an "and / or" relationship. For specific understanding, please refer to the context.

[0118] In this disclosure, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" can mean: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or plural.

[0119] It should be understood that in various embodiments of the present invention, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0120] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A heat treatment method for improving the room temperature plasticity of TiAl alloy, characterized in that: The heat treatment method for improving the room temperature plasticity of TiAl alloy comprises the following steps: S1. Raw material weighing: weigh the raw materials according to the atomic content ratio of the chemical composition of TiAl alloy; S2. Vacuum melting and casting: The raw material weighed in S1 is melted in a copper crucible of a vacuum induction levitation melting furnace, and then cast into a stainless steel mold and cooled to room temperature with the furnace to obtain a cast TiAl alloy ingot; S3, hot isostatic pressing: hot isostatic pressing the S2 cast TiAl alloy ingot to obtain a hot isostatically pressed alloy; S4. High temperature heat treatment: The S3 hot isostatically pressed alloy is subjected to high temperature heat treatment to obtain a TiAl alloy with a near lamellar structure.

2. The heat treatment method for improving the room temperature plasticity of TiAl alloy according to claim 1, characterized in that: The chemical composition atomic content ratio of the TiAl alloy in S1 is: Al 46-50at%, Nb 1-4at%, Cr 1-4at%, Si 0-0.4at%, and the balance is Ti and unavoidable impurity elements.

3. The heat treatment method for improving the room temperature plasticity of TiAl alloy according to claim 1, characterized in that: The raw materials in S1 are pure metal sponge titanium with a purity of 99.99%, aluminum ingots, chromium powder, silicon powder, and aluminum-niobium master alloy with a niobium mass fraction of 73.2%.

4. The heat treatment method for improving the room temperature plasticity of TiAl alloy according to claim 1, characterized in that: When the melting power in S2 is 100-120W, the alloy is kept for 5 minutes after being completely melted to allow the molten alloy liquid to fully mix and react; in addition, the melting needs to be repeated 2-3 times to obtain a TiAl alloy ingot with uniform composition.

5. The heat treatment method for improving the room temperature plasticity of TiAl alloy according to claim 1, characterized in that: The hot isostatic pressing process parameters of S3 are as follows: temperature controlled in the range of 1200-1330℃, pressure of 150-200MPa, holding time of 2-10h, and furnace cooling.

6. The heat treatment method for improving the room temperature plasticity of TiAl alloy according to claim 1, characterized in that: The microstructure of the hot isostatically pressed S3 alloy is a dual-state microstructure consisting of lamellar clusters and equiaxed γ grains.

7. The heat treatment method for improving the room temperature plasticity of TiAl alloy according to claim 1, characterized in that: The S4 medium and high temperature heat treatment is carried out in a muffle furnace. The process parameters are temperature control in the range of 1250-1360℃, heating rate of 10-20℃ / min, holding time of 0-10h, and air cooling.

8. The heat treatment method for improving the room temperature plasticity of TiAl alloy according to claim 1, characterized in that: The TiAl alloy with near-lamellar structure in S4 is composed of fine lamellar clusters, equiaxed γ grains and extremely fine lamellar clusters with nano-lamellar layers within the equiaxed γ grains; the extremely fine lamellar clusters within the equiaxed γ grains are only 5-20μm in size, and the interlamellar spacing is 5-60nm; the α2 phase content is 5-15%, and the γ phase content is 85-95%.

9. The heat treatment method for improving the room temperature plasticity of TiAl alloy according to claim 1, characterized in that: The mechanical properties of the TiAl alloy with near lamellar structure in S4 were tested, and the tensile rate at room temperature was 1.0×10 ‐4 s ‐1 The tensile strength is 600-660MPa, the yield strength is 430-490MPa, the elongation after fracture is 1.0-1.8%, and the room temperature plasticity is increased by 60-90% compared with the cast state.

10. The heat treatment method for improving the room temperature plasticity of TiAl alloy according to claim 1, characterized in that: The composition of the TiAl alloy with lamellar structure in S4 is Ti-47Al-2Cr-2Nb-0.2Si. The alloy was subjected to hot isostatic pressing at a temperature of 1310℃, a pressure of 150MPa, and a time of 4h, followed by furnace cooling. The alloy after hot isostatic pressing was subjected to high-temperature heat treatment at a temperature of 1310℃, a time of 4h, and air cooling. A room temperature tensile test was conducted at a tensile rate of 1.0×10 ‐4 s ‐1 The room temperature tensile results show that the tensile strength of Ti-47Al-2Cr-2Nb-0.2Si alloy is 644MPa, the elongation after fracture is 1.84%, and the room temperature plasticity is improved by 90% compared with the cast state.

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