A preparation method of a metastable beta titanium alloy three-state structure

Abstract

The application discloses a preparation method of a metastable beta titanium alloy three-state structure, which comprises the following steps: firstly, using high-energy pulse current rapid heating technology to heat the titanium alloy as a whole; secondly, using medium-temperature short-time heat preservation treatment to obtain a small amount of micron-sized alpha lath; finally, continuing to use low-temperature aging treatment to promote the precipitation of nanometer-sized alpha lamella, so that fine nanometer alpha lamella is dispersedly distributed, and finally, a new three-state structure containing equiaxed alpha phase, micron-sized lath alpha phase and uniform nanometer lamella alpha phase is obtained in the titanium alloy; by adjusting the process parameters of pulse electric heating and pseudo-amplitude decomposition mechanism, the three-state structure can be quickly and efficiently prepared in the metastable beta titanium alloy; compared with the traditional titanium alloy structure, the three-state structure is beneficial to improving the comprehensive mechanical properties of the alloy; the preparation method is environment-friendly and economical, simple to operate, improves the efficiency and reduces the energy consumption, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of titanium alloy heat treatment, and particularly relates to a preparation method of a metastable beta titanium alloy three-state structure. BACKGROUND

[0002] Titanium alloy has been widely used in key load-bearing components in the fields of aerospace and others due to its high specific strength, excellent corrosion resistance and fatigue resistance. The poor matching of strength and plasticity is a difficult and hot issue in the field of titanium alloy research. Once the chemical composition of the alloy is determined, heat treatment technology is an effective means to adjust the matching of strength and plasticity of the alloy. Generally, the microstructure of titanium alloy can be divided into four types according to the differences in the structure form, namely, equiaxed structure, lamellar structure, basketweave structure and duplex structure. However, the four types of structures improve the overall mechanical properties of the alloy to some extent, but there is still a contradiction that the strength is improved at the expense of plasticity. For example, equiaxed structure has high plasticity and low strength, lamellar structure has high strength and low plasticity, and so on. Therefore, the current structure type and heat treatment technology cannot meet the performance requirements of high strength and toughness titanium alloy, and therefore a multiple heat treatment process is developed to precisely control the structure form, phase content and size of the alloy by adjusting the coordination between the solution and aging temperature and time and the cooling method, so as to maximize the performance potential of the alloy. At present, researchers have developed a heat treatment technology to successfully prepare a three-state structure in high strength and toughness titanium alloy. However, due to the need for forging near the phase transition point, the difficulty of structure control is increased, which seriously affects the control and popularization and application of the three-state structure of titanium alloy. SUMMARY

[0003] In view of the above problems of the prior art, the purpose of the present application is to provide a preparation method of a metastable beta titanium alloy three-state structure. The high-energy pulse current rapid heating technology is used for the first time to study the structure control of high-strength titanium alloy, and a three-state structure containing equiaxed alpha phase, coarse lath alpha phase and nanometer alpha phase is obtained. The strong and tough effects of different scale alpha phases are organically combined, so as to improve the matching of strength and plasticity of the alloy. The present application provides a heat treatment method for preparing a three-state structure with three morphologies of alpha phase for a typical high-strength Ti55531 alloy used in aerospace; and a heat treatment method for obtaining an excellent matching of strength and plasticity and preparing a structure design for a complex multi-phase alloy.

[0004] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0005] A preparation method of a metastable beta titanium alloy three-state structure, comprising the following steps:

[0006] Step 1, a plate or round bar sample is prepared by using wire cut electrical discharge, the sample is metastable Ti55531 titanium alloy, and the nominal composition is Ti-5Al-5Mo-5V-3Cr-1Zr;

[0007] Step 2, the plate or round bar sample in step 1 is put into a glove box, and the sample is connected with the positive and negative poles of a high-energy pulse power supply;

[0008] Step 3, the glove box is vacuumized, the vacuum degree is 3.5 KPa, then inert gas protection is conducted, and the gas pressure is kept at 80-85 KPa to prevent the sample from being oxidized;

[0009] Step 4, the pulse power supply is turned on, the pulse voltage is adjusted to 45-50 V, the current and the pulse frequency are adjusted, the titanium alloy sample is heated, and the heating time is 5-10 minutes;

[0010] Step 5, the titanium alloy plate or round bar sample after the pulse current heating treatment is put into a box-type heat treatment furnace for pseudo-amplitude decomposition mechanism process treatment, and the specific process is as follows: first, the sample is placed in a heat treatment furnace at a temperature of 760-800 DEG C, and the holding time is 27-32 minutes; then, the sample is placed in a heat treatment furnace at a temperature of 500-600 DEG C, and the holding time is 200-250 minutes, and then the sample is cooled to room temperature, so that the titanium alloy tri-state structure is obtained.

[0011] Further, the cross-sectional area of the sample in step 1 is 4-15 mm 2 .

[0012] Further, the specific method for connecting the sample with the positive and negative poles of the high-energy pulse power supply in step 2 is that the positive and negative poles of the pulse power supply are clamped to the two ends of the sample to be heated by using copper-zinc alloy plates.

[0013] Further, high-purity inert gas argon is used in step 3.

[0014] Compared with the prior art, the present application has the beneficial effects:

[0015] 1. The present application does not need to change the alloy composition, nor does it need to be subjected to hot working treatment such as forging and rolling, but only by adjusting the pulse electric heating parameters and time, the tri-state structure prepared by the traditional hot working method can be obtained in a short time;

[0016] 2. The high-energy pulse current heating effectively inhibits the abnormal coarsening of the beta grains, and lays a good organizational foundation for the subsequent precipitation and regulation of different morphologies of alpha phase;

[0017] 3. The present application combines the advantages of pulse current and "pseudo-amplitude decomposition mechanism" process, designs and prepares a tri-state structure mode in which micron equiaxial shape, lath shape and nanometer size alpha coexist, and the formation of continuous grain boundary alpha phase is effectively inhibited.

[0018] 4、The tri-state organization is composed of hard nanometer-sized lamellar alpha phase and relatively soft micron-sized equiaxed and lath alpha phase, which combines the toughening effect of micron-sized alpha phase and the strengthening effect of nano alpha particles, effectively improves the plasticity and toughness of the alloy without significantly reducing the strength of the alloy.

[0019] 5、The electric pulse heating method is simple in operation, fast in heat treatment speed, high in efficiency, free of harmful gas generation, economic and environmentally friendly, can improve the production efficiency of materials, and can reduce energy consumption, is a very competitive heat treatment technology, and has a wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The titanium alloy tri-state organization structure prepared for the embodiment 1 of the present application.

[0021] Figure 2 The titanium alloy tri-state organization structure prepared for the embodiment 2 of the present application.

[0022] Figure 3 The titanium alloy tri-state organization structure prepared for the embodiment 3 of the present application. DETAILED DESCRIPTION

[0023] The present application will be described in detail below with reference to the accompanying drawings. The present application takes the original material Ti55531 alloy sample as an example to further illustrate the specific implementation of preparing a multi-scale lamellar structure by using pulse current heating.

[0024] A preparation method of a metastable beta titanium alloy tri-state organization, which is implemented according to the following steps:

[0025] Step 1: Use electric spark wire cutting to prepare a plate or round bar sample, the sample is a metastable Ti55531 titanium alloy, the nominal composition of which is Ti-5Al-5Mo-5V-3Cr-1Zr, and the cross-sectional area of the alloy sample is 4-15mm 2 ;

[0026] Step 2: Put the above plate or round bar sample into a glove box, and connect the sample to the positive and negative electrodes of a high-energy pulse power supply, the positive and negative electrodes of the pulse power supply are copper-zinc alloy plates with a size of 50*200*5mm, and the copper-zinc alloy plates are used to clamp the two ends of the sample to be heated;

[0027] Step 3: Perform vacuum treatment on the glove box, and then introduce inert gas for protection, the vacuum degree is 3.5KPa, and the gas pressure of high-purity inert gas is maintained at 80-85KPa;

[0028] Step 4: Turn on the pulse power supply, adjust the pulse voltage, current and pulse frequency, and quickly heat treat the titanium alloy sample. The pulse voltage is 45-50V, the continuous heating time is 5-10 minutes. The pulse current is used to quickly heat the sample, which causes the original structure to quickly transform into beta phase. Then, the beta matrix is quickly cooled, which does not allow the alpha phase in the beta matrix to fully precipitate. Finally, the equiaxed alpha phase and pure beta matrix structure is obtained.

[0029] Step 5: First, place the titanium alloy plate or round bar sample treated by pulse current heating in a heat treatment furnace at a temperature of 760-800℃ for 27-32 minutes. Use medium-high temperature short time annealing to precipitate a small amount of alpha phase in the beta matrix and grow rapidly at this temperature to precipitate micron and sub-micron size lath alpha phase. Then, place the sample in a heat treatment furnace at 500-600℃ for 200-250 minutes and air cool to room temperature. This is a heat treatment at the temperature where the alloy undergoes pseudo-amplitude decomposition mechanism, which allows uniform nucleation of alpha phase and increases its nucleation rate, effectively inhibiting the growth speed of alpha phase, and obtaining nanometer-sized needle-like alpha phase. This is a titanium alloy three-state structure with micron equiaxed alpha phase, micron lath alpha phase and nanometer-sized needle-like alpha phase.

[0030] Example 1

[0031] (1) Select a Ti55531 titanium alloy sample in the form of a round bar;

[0032] (2) Place the Ti55531 titanium alloy sample in the form of a plate into a glove box and connect the sample to the positive and negative copper-zinc alloy plate electrodes of the pulse power supply;

[0033] (3) Vacuumize the glove box to a vacuum degree of 3.5KPa, then fill high-purity argon gas into the glove box to maintain a gas pressure of 80KPa to prevent oxidation of the sample;

[0034] (4) Turn on the pulse power supply, turn on the pulse power switch, adjust the pulse voltage to 45V, and heat for 7 minutes. Air cool to room temperature;

[0035] (5) Place the sample treated by pulse current heating in a heat treatment furnace at a temperature of 780℃ for 32 minutes, then directly place the sample in a heat treatment furnace at 550℃ for 200 minutes, and air cool to room temperature to obtain a titanium alloy three-state structure.

[0036] After the sample treated by pulse current heating is coarsely ground, finely ground and electrolytically polished, it is etched using a mixed solution of HF:HNO3:H2O in a ratio of 1:2:5, and the microstructure of the sample is observed and analyzed using a scanning electron microscope. Figure 1The scanning picture of the obtained test block shows that the microstructure contains equiaxed α phase (average diameter 2.7 μm), micron-sized platelet α phase (average width 0.6 μm) and nanometer-sized fine α phase (average width 80 nm), i.e. a tri-modal structure containing equiaxed α, platelet α and fine nanometer α phase.

[0037] Example 2

[0038] (1) First, the original Ti55531 alloy was cut into a plate-shaped sample with a cross-sectional area of 15 mm 2 ;

[0039] (2) The sample was connected to the positive and negative copper-zinc alloy plate electrodes of the pulse power supply and placed in a glove box;

[0040] (3) The glove box was vacuumed to a vacuum degree of 3.5 KPa, and then high-purity argon was filled in the glove box to maintain a gas pressure of 82 KPa to prevent the sample from being oxidized;

[0041] (4) The pulse power supply was turned on, the pulse power supply switch was turned on, the pulse voltage was adjusted to 47 V, the heating time was 5 minutes, and then the sample was air-cooled to room temperature;

[0042] (5) After the sample was heated and treated by the pulse current, the sample was directly placed in a 600°C oven for 240 minutes, and then air-cooled to room temperature.

[0043] After the sample heated and treated by the pulse current was coarsely ground, finely ground and electrolytically polished, the sample was etched using a mixed solution of HF:HNO3:H2O in a ratio of 1:2:5, and the microstructure of the sample was observed and analyzed using a scanning electron microscope. Figure 2 The scanning picture of the obtained test block shows that the microstructure contains equiaxed α phase (average diameter 2.7 μm), micron-sized platelet α phase (average width 0.6 μm) and nanometer-sized fine α phase (average width 80 nm), i.e. a tri-modal structure containing equiaxed α, platelet α and fine nanometer α phase.

[0044] Example 3

[0045] (1) First, the original Ti55531 alloy was cut into a plate-shaped sample with a cross-sectional area of 4 mm 2 ;

[0046] (2) The sample was connected to the positive and negative copper-zinc alloy plate electrodes of the pulse power supply and placed in a glove box;

[0047] (3) The glove box was vacuumed to a vacuum degree of 3.5 KPa, and then high-purity argon was filled in the glove box to maintain a gas pressure of 85 KPa to prevent the sample from being oxidized;

[0048] (4) Turn on the pulse power supply, open the pulse power supply switch, adjust the pulse voltage to 50V, and heat for 10 minutes, and then air cool to room temperature;

[0049] (5) After the sample after pulse current heating treatment is continuously kept at 800℃ for 27 minutes, the sample is continuously kept at 500℃ for 250 minutes, and then air cooled to room temperature.

[0050] After the heat-treated sample is coarsely ground, finely ground and electrolytically polished, the sample is etched by using a mixed solution of HF:HNO3:H2O in a ratio of 1:2:5. In the alloy structure, there are equiaxed α phase (average diameter of 2.1 μm), sub-micron size lath α phase (average width of 0.8 μm) and nanometer size fine α phase (average width of 90 nm), i.e. a tri-modal structure including equiaxed α phase, lath α phase and fine lamellar α phase is formed.

[0051] In the present application, the Ti55531 alloy obtains a tri-modal structure by high-energy pulse current heating composite treatment technology. Compared with the conventional structure type, the tri-modal structure includes α phase of different scales, which is beneficial to realize excellent strength-plasticity matching.

[0052] Although the specific embodiments of the present application are described above, those skilled in the art should understand that this is only an example, and the protection scope of the present application is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present application, and these changes and modifications all fall within the protection scope of the present application.

Claims

1. A method for preparing a metastable β-titanium alloy with three-state microstructure, characterized in that, Includes the following steps: Step 1: Prepare plate-shaped or round bar samples by wire electrical discharge machining. The samples are metastable Ti55531 titanium alloy with a nominal composition of Ti-5Al-5Mo-5V-3Cr-1Zr. Step 2: Place the plate-shaped or round bar sample described in Step 1 into the glove box and connect the sample to the positive and negative terminals of the high-energy pulse power supply. Step 3: Evacuate the glove box to a vacuum level of 3.5 kPa, then introduce inert gas for protection, maintaining the gas pressure at 80-85 kPa to prevent the sample from being oxidized; Step 4: Connect the pulse power supply, adjust the pulse voltage to 45-50V, current and pulse frequency, and heat the titanium alloy sample for 5-10 minutes. Step 5: Place the titanium alloy plate or bar sample after pulsed current heating treatment into a box-type heat treatment furnace for pseudo-amplitude decomposition process. The specific process is as follows: First, place the sample in a heat treatment furnace at a temperature of 760-800℃ and hold for 27-32 minutes; then, place the sample in a heat treatment furnace at a temperature of 500-600℃ and hold for 200-250 minutes, and cool to room temperature to obtain the three-state microstructure of titanium alloy.

2. The method for preparing a metastable β-titanium alloy tri-state microstructure according to claim 1, characterized in that, The sample cross-sectional area in step 1 is 4-15 mm². 2 .

3. The method for preparing a metastable β-titanium alloy tri-state microstructure according to claim 1, characterized in that, The specific method for connecting the sample to the positive and negative terminals of the high-energy pulse power supply in step 2 is as follows: the positive and negative terminals of the pulse power supply are clamped at both ends of the sample to be heated using copper-zinc alloy plates.

4. The method for preparing a metastable β-titanium alloy tri-state microstructure according to claim 1, characterized in that, In step 3, high-purity inert gas argon is used.

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