A high-temperature and cryogenic combined forging method for preparing isomeric equiaxed structure titanium alloy forgings

Abstract

The application aims to provide a high-temperature-low-temperature combined forging method for preparing isomeric equiaxed structure titanium alloy forgings, and belongs to the technical field of titanium alloy forging processes.The application obtains a dual-state structure titanium alloy composed of coarse equiaxed grains and fine lamellar grains through high-temperature forging and heat treatment; the fine lamellar grains are broken into fine equiaxed grains without damaging the coarse equiaxed grains through deep cold forging. Finally, the isomeric equiaxed structure titanium alloy forgings with coarse equiaxed grains and fine equiaxed grains are obtained based on the synergistic effect of high-temperature forging and deep cold forging. Compared with the traditional process for preparing gradient materials, the application can realize the uniform distribution of isomeric structure in the forgings, and can precisely control the structure based on the forging parameters, and the process flow is simple and easy to produce.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy forging technology, specifically relating to a high-temperature-deep cryogenic composite forging method for preparing titanium alloy forgings with heterogeneous equiaxed structures. Background Technology

[0002] Titanium alloys are widely used in aerospace, chemical, transportation, and biomedical fields due to their high specific strength, high corrosion resistance, good high-temperature performance, and excellent biocompatibility. In the biomedical field, β-titanium alloys are gradually replacing traditional biomedical metal materials such as stainless steel and cobalt-based alloys as the preferred choice for medical implants, showing broad market prospects. However, β-titanium alloys struggle to simultaneously meet the requirements of high strength and high ductility. Traditional strengthening methods reduce alloy ductility, leading to decreased material formability and failure during service.

[0003] Heterogeneous metallic materials exhibit superior overall performance compared to traditional homogeneous metallic materials, maintaining good ductility and toughness while achieving high strength. This is due to their multi-scale heterogeneous microstructure, which simultaneously contains coarse and fine grains. The coarse grains possess excellent plastic deformation capacity and suppress crack initiation and propagation during deformation, while the fine grains have a higher yield strength compared to the coarse grains, contributing significantly to the improvement of the alloy's strength and hardness. Therefore, introducing heterogeneous structures into titanium alloys can achieve a "win-win" situation in terms of both strength and ductility.

[0004] Publication No. CN111659747A proposes a method for obtaining heterogeneous metal sheets using composite stamping. This method employs a pair of conjugate dies for heated stamping, followed by heat treatment to form heterogeneous laminated metal sheets. However, this technique has the following problems: (1) it can only produce heterogeneous metal sheets; (2) the heterogeneous structure is unevenly distributed overall, and the connection effect of the laminated materials is difficult to guarantee. Publication No. CN114369772A proposes a method for preparing gradient metal materials with high elongation, mainly involving torsional deformation and heat treatment processes. However, this technique has the following problems: (1) it can only produce gradient structure rods; (2) the alloy surface layer obtained by this method has a nanostructure, and the central layer has a coarse-grained structure, making it difficult to prepare a structure with a uniform distribution of coarse and fine grains overall. Publication No. CN103320734A proposes a method for producing medical fine-grained titanium / titanium alloy rods, which includes a phase transformation point T... β The above, T β The following combined multi-directional upsetting deformation method can obtain fine-grained structures, but it cannot prepare gradient structures and heterogeneous structures containing coarse and fine grains.

[0005] In addition, publication numbers CN102764839A, CN102581188A, CN101648254A, CN112676503A, and CN110814250A all involve forging methods for titanium alloys, but based on the above processes, it is impossible to prepare a uniform heterogeneous structure containing both coarse and fine grains. Summary of the Invention

[0006] This invention addresses the problems existing in the prior art by proposing a high-temperature-deep cryogenic composite forging method for preparing titanium alloy forgings with heterogeneous equiaxed structures. The titanium alloy forgings prepared by this method are composed of a mixture of coarse and fine equiaxed grains, and the heterogeneous equiaxed grains are uniformly distributed within the forging. This method is simple, easy to implement, and readily applicable to industrial production.

[0007] The present invention adopts the following technical solution:

[0008] A high-temperature-deep-cryogenic composite forging method for preparing heterogeneous equiaxed titanium alloy forgings involves obtaining a dual-phase titanium alloy with coarse equiaxed grains and fine lamellar grains through high-temperature forging and heat treatment; breaking the fine lamellar grains into fine equiaxed grains through deep-cryogenic forging without destroying the coarse equiaxed grains; and finally, obtaining a heterogeneous equiaxed titanium alloy forging with inclusions of coarse and fine equiaxed grains based on the synergistic effect of high-temperature forging and deep-cryogenic forging. The method specifically includes the following steps:

[0009] The first step is to heat the titanium alloy billet to a temperature 30°C above the phase transformation point and hold it for 15-30 minutes to obtain a uniform β phase structure. After holding, the billet is air-cooled to room temperature to obtain a lamellar α phase structure.

[0010] The second step is to heat the billet after the first heat treatment to 30-50°C below the phase transformation point, hold it at that temperature for 15-30 minutes, and then perform isothermal forging. After forging, air cool it to room temperature.

[0011] The third step is to heat the billet after the second step forging to 30-80°C below the phase transformation point and perform recrystallization annealing. After annealing, air cool to room temperature to obtain a dual-state titanium alloy.

[0012] The fourth step is to weld an R-type thermocouple to the center of the side of the forging after the third step to monitor the temperature change of the forging during the subsequent cryogenic forging process. Then, the forging is immersed in liquid nitrogen for 30 minutes to make the internal temperature evenly distributed.

[0013] The fifth step involves cryogenic forging the titanium alloy sample treated in the fourth step under a liquid nitrogen atmosphere. This process breaks the fine lamellar grains into fine equiaxed grains, while the coarse equiaxed grains remain almost unchanged. After forging, the forging is placed in a room temperature environment and slowly restored to room temperature to obtain the final product.

[0014] Furthermore, the deformation rate of the isothermal forging described in the second step is 0.01 / s to 1.0 / s, and the deformation is 10%-50%.

[0015] Furthermore, the annealing time described in the third step is 30-120 mins.

[0016] Furthermore, the deformation rate of the cryogenic forging described in step five is 0.01 / s to 0.1 / s, and the deformation is 10%-30%.

[0017] The purpose of the high-temperature forging and heat treatment in the above process is to obtain a dual-phase titanium alloy, that is, an alloy composed of coarse equiaxed grains and fine lamellar grains. The purpose of cryogenic forging is to break the fine lamellar grains into fine equiaxed grains, while the coarse equiaxed grains remain almost unchanged during cryogenic forging. Ultimately, based on the synergistic effect of high-temperature forging and cryogenic forging, a titanium alloy forging with a heterogeneous equiaxed microstructure and inclusions of coarse and fine equiaxed grains is obtained.

[0018] The beneficial effects of this invention are:

[0019] 1) Traditional forming processes for obtaining heterogeneous titanium alloys are mostly complex and cumbersome, requiring high-end molds and equipment. This invention only requires three main processes: high-temperature forging, heat treatment, and cryogenic forging to obtain heterogeneous titanium alloys, which greatly simplifies the processing of titanium alloys and eliminates the need for expensive molds.

[0020] 2) Traditional heterostructure titanium alloys are mostly gradient structures, that is, fine grains on the surface and coarse grains inside. It is difficult to achieve an alternating distribution of coarse and fine grains in the alloy as a whole. This invention introduces coarse grain structure through high temperature forging and heat treatment, and introduces fine grain structure through deep cryogenic forging. Finally, a microstructure with uniform distribution of coarse equiaxed grains and fine equiaxed grains can be obtained. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the process of the present invention;

[0022] Figure 2 This is a schematic diagram of cryogenic forging.

[0023] Wherein: 1-Thermocouple; 2-Upper anvil; 3-Liquid nitrogen; 4-Sample; 5-Liquid nitrogen container; 6-Lower anvil;

[0024] Figure 3 The microstructure of the central region of the Ti-6Al-4V titanium alloy forging after cryogenic forging. Detailed Implementation

[0025] The invention will be described in more detail below with reference to examples.

[0026] Example 1

[0027] The raw material used in this embodiment is α+β type titanium alloy Ti-6Al-4V, and the experimentally measured β→α phase transformation temperature (T) β The temperature is approximately 989℃. The specific experimental procedure and process parameters are as follows:

[0028] (1) The titanium alloy billet (sample 1) was heated from room temperature to 1019℃ (T β The temperature was increased to +30℃, with a heating rate of 10℃ / s, and then held at 1019℃ for 15 mins to obtain a uniform microstructure. After the holding period, the titanium alloy billet was air-cooled to room temperature.

[0029] (2) Heat the heat-treated billet to 959℃ (T β -30℃), held at this temperature for 15 minutes, then isothermal forging was performed with a deformation rate of 0.01 / s and a deformation of 30%. After forging, the material was air-cooled to room temperature.

[0030] (3) Heat the forged billet to 959℃ (T β Annealed at -30℃ for 60 minutes, then air-cooled to room temperature. The microstructure of the central region of the forging is as follows: Figure 1 As shown;

[0031] (4) Weld an R-type thermocouple to the center of the side of the forging to monitor the temperature change of the forging during the subsequent cryogenic forging process. Then immerse the forging in liquid nitrogen for 30 minutes to ensure uniform internal temperature distribution;

[0032] (5) The titanium alloy sample was cryogenically forged in a liquid nitrogen atmosphere at a deformation rate of 0.05 / s and a deformation of 25%. After forging, the forging was slowly restored to room temperature. The microstructure of the central region of the forging is as follows: Figure 3 As shown in (a).

[0033] Example 2

[0034] The raw material used in this embodiment is α+β type titanium alloy Ti-6Al-4V, and the experimentally measured β→α phase transformation temperature (T) β The temperature is approximately 989℃. The specific experimental procedure and process parameters are as follows:

[0035] (1) The titanium alloy billet (sample 2) was heated from room temperature to 1019℃ (T β The temperature was increased to +30℃, with a heating rate of 10℃ / s, and then held at 1019℃ for 15 mins to obtain a uniform microstructure. After the holding period, the titanium alloy billet was air-cooled to room temperature.

[0036] (2) Heat the heat-treated billet to 959℃ (Tβ-30℃), hold it for 15 mins and then perform isothermal forging. The deformation rate is 0.01 / s and the deformation is 30%. After forging, air cool to room temperature.

[0037] (3) Heat the forged billet to 959℃ (T β Annealed at -30℃ for 60 minutes, then air-cooled to room temperature. The microstructure of the central region of the forging is as follows: Figure 1 As shown;

[0038] (4) Weld an R-type thermocouple to the center of the side of the forging to monitor the temperature change of the forging during the subsequent cryogenic forging process. Then immerse the forging in liquid nitrogen for 30 minutes to ensure uniform internal temperature distribution;

[0039] (5) The titanium alloy sample was cryogenically forged in a liquid nitrogen atmosphere at a deformation rate of 0.01 / s and a deformation of 25%. After forging, the forging was slowly restored to room temperature. The microstructure of the central region of the forging is as follows: Figure 3 As shown in (b).

Claims

1. A high temperature - cryogenic combined forging method for producing a wrought forging of isomeric equiaxed titanium alloy, characterized in that: A titanium alloy with a dual microstructure consisting of coarse equiaxed grains and fine lamellar grains is obtained through high-temperature forging and heat treatment. The fine lamellar grains are then broken into fine equiaxed grains through cryogenic forging without damaging the coarse equiaxed grains. Finally, based on the synergistic effect of high-temperature forging and cryogenic forging, a titanium alloy forging with a heterogeneous equiaxed microstructure containing coarse and fine equiaxed grains is obtained. The specific steps include the following: The first step is to heat the titanium alloy billet to a temperature 30°C above the phase transformation point and hold it for 15-30 minutes to obtain a uniform β phase structure. After holding, the billet is air-cooled to room temperature to obtain a lamellar α phase structure. The second step is to heat the billet after the first heat treatment to 30-50°C below the phase transformation point, hold it at that temperature for 15-30 minutes, and then perform isothermal forging. After forging, air cool it to room temperature. The third step is to heat the billet after the second step forging to 30-80°C below the phase transformation point and perform recrystallization annealing. After annealing, air cool to room temperature to obtain a dual-state titanium alloy. The fourth step is to weld an R-type thermocouple to the center of the side of the forging after the third step to monitor the temperature change of the forging during the subsequent cryogenic forging process. Then, the forging is immersed in liquid nitrogen for 30 minutes to make the internal temperature evenly distributed. The fifth step involves cryogenic forging the titanium alloy sample treated in the fourth step under a liquid nitrogen atmosphere. This process breaks the fine lamellar grains into fine equiaxed grains, while the coarse equiaxed grains remain almost unchanged. After forging, the forging is placed in a room temperature environment and slowly restored to room temperature to obtain the final product.

2. The high-temperature-deep cryogenic composite forging method for preparing heterogeneous equiaxed titanium alloy forgings according to claim 1, characterized in that: The deformation rate of the isothermal forging described in the second step is 0.01 / s to 1.0 / s, and the deformation is 10%-50%.

3. The high-temperature-deep cryogenic composite forging method for preparing heterogeneous equiaxed titanium alloy forgings according to claim 1, characterized in that: The annealing time mentioned in step three is 30-120 minutes.

4. The high temperature-subzero combined forging method for preparing isomeric equiaxed structure titanium alloy forgings according to claim 1, characterized in that: The deformation rate of the cryogenic forging described in step 5 is 0.01 / s to 0.1 / s, and the deformation is 10%-30%.

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