Preparation method of α single crystal of titanium alloy

Abstract

This invention discloses a method for preparing α-crystals of titanium alloys, belonging to the field of non-ferrous metallurgical technology. The method is as follows: (1) Heat-treating a large-size Ti-6Al-4V alloy ingot in the β single-phase region to obtain an ingot with large-sized β grains; (2) β grain sampling: Selecting a specific orientation for the ingot and cutting out large-sized titanium alloy β grains; (3) Applying constant tensile or compressive stress to the β grains while simultaneously performing heat treatment, and unloading the stress after furnace cooling to room temperature to obtain a sample containing α-crystals; (4) Observing the obtained sample using scanning electron microscopy and performing EBSD analysis to obtain information such as the morphology, size, and crystal orientation of the α phase layers in the sample; (5) Selecting a suitable sample angle to peel out the α-crystals. This invention can prepare titanium alloy α-crystals with a width on the order of millimeters, providing an ideal material for the study of the mechanical behavior of titanium alloys.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal metallurgy technology, specifically to a method for preparing titanium alloy α single crystals. Background Technology

[0002] Single crystals can lay the foundation for studying the deformation mechanism and mechanical properties of polycrystalline materials, but alloys such as titanium and titanium alloys that have solid-state phase transformations generally form polymorphs during the phase transformation, making it difficult to prepare single crystals.

[0003] Currently, the preparation of titanium alloy single crystals mainly employs directional solidification methods. In the absence of a seed crystal, single crystals can be obtained through inter-grain competition growth; with a seed crystal, single crystals with a seed crystal orientation can be prepared. However, the preparation of α-phase single crystals is rarely reported. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing α single crystals of titanium alloys. This method prepares millimeter-scale α single crystals by means of solid-state phase transformation under applied tensile / compressive stress, providing an ideal material for the study of the mechanical behavior of titanium alloys.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing α-crystals of titanium alloy includes the following steps:

[0007] (1) Generate larger β grains: Heat treat the large-size Ti-6Al-4V alloy ingot in the β single-phase region and furnace cool it to room temperature to obtain an ingot with larger β grains.

[0008] (2) β grain sampling: After scanning electron microscopy and EBSD analysis of the internal region of the ingot with large β grains, select a specific orientation and cut out the large titanium alloy β grains to obtain β grain samples.

[0009] (3) Applying tensile / compression load: The β-crystal sample obtained in step (2) is loaded into a tensile / compression device, vacuumed, and then filled with argon for protection; then a constant tensile or compressive stress is applied along a specific direction, and heat treatment is performed at the same time. After the furnace is cooled to room temperature, the stress is unloaded to obtain a sample containing α single crystals.

[0010] (4) The sample obtained after step (3) is observed by scanning electron microscopy and analyzed by EBSD to obtain information such as the morphology, size and crystal orientation of the α phase layer in the sample.

[0011] (5) Single crystal selection: Based on the observation and analysis results in step (4), select a suitable sample angle to peel out the α single crystal.

[0012] In step (1) above, the ingot is a cylindrical ingot with a diameter greater than 40cm.

[0013] In step (1) above, the heat treatment temperature is preferably 950-1050℃ and the holding time is 0.5-1.5h. This heat treatment process can generate larger β grains.

[0014] In step (2) above, selecting a specific orientation and cutting larger titanium alloy β grains means: selecting <100> orientation, <110> Orientation or <111> The titanium alloy β grains are cut from opposite sides of the β grains.

[0015] In step (3) above, the direction of the applied tensile or compressive stress is perpendicular to the specific orientation in step (2); the tensile or compressive stress is 10-50 MPa.

[0016] In step (3) above, the heat treatment process is as follows: first, heat the Ti-6Al-4V alloy to the β single-phase region and hold for 20-30 min; then slowly lower the temperature to 10-20°C below the alloy phase transformation point, hold for 24 h, and then cool the furnace to room temperature to allow the α phase to grow slowly.

[0017] In step (3) above, when the applied external load is 10-50 MPa, it can ensure that the material is within the elastic range; when the heat treatment is carried out at 10-20℃ below the alloy phase transformation point, the nucleation of α phase is reduced, which is beneficial to single crystal preparation.

[0018] In step (3) above, the thickness of the α phase layer can be stably controlled in the millimeter range by applying external load and heat treatment process.

[0019] The advantages and features of this invention are as follows:

[0020] (1) In the solid-state phase transformation process of titanium alloy, the present invention utilizes the selective effect of external stress on α variants to control the nucleation and growth of only a few variants, without the need for seed crystals;

[0021] (2) This invention uses external stress to regulate the selection of variants to promote the growth of fewer variants, thus realizing the preparation of millimeter-scale α single crystals;

[0022] (3) The method of the present invention is simple and easy to operate, with a short cycle, and is convenient for laboratory operation. Attached Figure Description

[0023] Figure 1 For phase field dynamics simulation of applied stress (τ=3×10) 4Prediction of the selection of α variants; where: (a) and (b) are the microstructure morphology and volume fraction of each variant under σ11=σ22=-50e-3GPa, respectively; (c) and (d) are the microstructure morphology and volume fraction of each variant under σ11=σ22=-100e-3GPa, respectively; at this time, the orientation of the external stress coordinate system is: u=0.597, v=-0.799, w=6.677e-2; r=0.547, s=0.345, t=-0.763; h=0.587, k=0.492, l=0.643. Detailed Implementation

[0024] To further understand the present invention, the present invention is described below with reference to examples. However, the examples are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention.

[0025] This invention utilizes external stress to control the types of precipitated phase variants, providing a basis for the preparation of α single crystals of titanium and titanium alloys. The effects of different applied stress conditions on the nucleation, growth, and microtexture evolution of the α phase in titanium and titanium alloys were investigated, such as... Figure 1 As shown, a reasonable external loading method was explored to control the precipitation of α variants in titanium and titanium alloys, providing a solution for the preparation of millimeter-scale α single crystals of titanium and titanium alloys.

[0026] Example 1:

[0027] This embodiment describes the preparation of titanium alloy α single crystals, and the process is as follows:

[0028] (1) A cylindrical Ti-6Al-4V alloy ingot with a diameter of 50cm was heat-treated in the β single-phase region at a temperature of 1010℃ for 1h and then cooled in the furnace to room temperature to obtain an ingot with larger β grains.

[0029] (2) After performing scanning electron microscopy and EBSD analysis on the internal region of the ingot with large β grains, select the 110 orientation (or 001 orientation or 100 orientation) to cut titanium alloy β grains on opposite sides of the β grains (the other two sides can be cut in any direction, just make sure to cut a complete β grain) to obtain β grain samples.

[0030] (3) The obtained β-grain sample was placed in a universal tensile testing machine, evacuated, and then filled with argon gas for protection; then along the direction perpendicular to the β-grain... <110> Orientation (or <100> Orientation or <111> A constant tensile or compressive stress (a value between 10-50 MPa) is applied in the orientation direction (whichever is perpendicular to the cutting direction), while heat treatment is performed. The heat treatment process is as follows: first, the temperature is raised to 1010℃ and held for 25 min; then, it is slowly lowered to 15℃ below the alloy phase transformation point and held for 24 h. After furnace cooling to room temperature, the stress is unloaded to obtain a sample containing α single crystals.

[0031] (4) The sample obtained in step (3) was observed by scanning electron microscopy and analyzed by EBSD to obtain information such as the morphology, size and crystal orientation of the α phase layer in the sample.

[0032] (5) Single crystal selection: Based on the observation and analysis results in step (4), select a suitable sample angle to peel out the α single crystal. Through analysis, the thickness of the α phase layer is on the order of millimeters.

Claims

1. A method of producing a titanium alloy alpha single crystal, characterized by: The method comprises the following steps: (1) generating large beta grains: heat treating a Ti-6Al-4V alloy large-size ingot in a beta single-phase region, furnace cooling to room temperature, and obtaining an ingot with large-size beta grains; (2) beta grain sampling: after scanning electron microscopy and EBSD analysis of the internal region of the large-size beta grain ingot, selecting a specific orientation and cutting a large-size titanium alloy beta grain to obtain a beta grain sample; (3) external tensile / compressive load: loading the beta grain sample obtained in step (2) into a tensile / compressive device, vacuumizing, and then filling argon for protection; then applying a constant tensile or compressive stress along a specific direction, and simultaneously performing heat treatment, furnace cooling to room temperature, and unloading the force to obtain a sample containing alpha single crystals; (4) observing and analyzing the sample obtained in step (3) by scanning electron microscopy and EBSD to obtain the alpha phase lamellar morphology, size, and crystal orientation information of the sample; (5) single crystal selection: selecting an appropriate sample angle to peel off an alpha single crystal according to the observation and analysis results in step (4); In step (3), the direction of the applied tensile or compressive stress is perpendicular to the specific orientation in step (2); the tensile or compressive stress is 10-50 MPa, In step (3), the heat treatment process is: first heating to the beta single-phase region of the Ti-6Al-4V alloy and maintaining for 20-30 min; then slowly reducing to 10-20 ℃ below the alloy phase transition point, maintaining for 24 h, and furnace cooling to room temperature to allow the alpha phase to grow slowly, In step (3), the thickness of the alpha phase lamella can be stably controlled in the millimeter order through the external load and heat treatment process.

2. The method of producing a titanium alloy alpha single crystal according to claim 1, characterized by: In step (1), the ingot is a cylindrical ingot with a diameter greater than 40 cm.

3. The method of producing a titanium alloy alpha single crystal of claim 1, wherein: In step (1), the heat treatment temperature is 950-1050 ℃, and the holding time is 0.5-1.5 h, which can realize the generation of large-size beta grains.

4. The method of producing a titanium alloy alpha single crystal of claim 1 wherein: In step (2), selecting a specific orientation and cutting a large-size titanium alloy beta grain means: selecting <100> orientation, <110> orientation, or <111> orientation to cut titanium alloy beta grains on opposite sides of the beta grain.

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