A method for controlling the number and size of multi-element titanium alloy grains

Abstract

The present invention discloses a method for controlling the number and size of multi-component titanium alloy grains, the method comprising: 1. preparing raw materials using high-purity Ti, Al, Mo, V, Fe, and Cr metals; 2. preparing spherical titanium alloys from the raw materials by high vacuum arc melting and vacuum laser melting; 3. placing the spherical titanium alloy in an electrostatic suspension system to melt and overheat to obtain an alloy melt; 4. rapidly solidifying the alloy melt under electrostatic suspension conditions to obtain a multi-component titanium alloy. The present invention effectively controls the number and size of multi-component titanium alloy grains through multi-component titanium alloy component design and extraordinary solidification, realizes direct control of the microstructure of the multi-component titanium alloy, does not require subsequent process effects, simplifies the preparation process while optimizing the organization, and obtains multi-component titanium alloy materials with different structures such as fine grains, twin crystals and single crystals to meet the needs of different application fields.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy preparation, and in particular relates to a method for controlling the number and size of multi-component titanium alloy grains. Background Art

[0002] Titanium alloys have excellent properties such as low density, high specific strength and good corrosion resistance. They have gradually replaced aluminum alloys and steels and are widely used in rockets, satellites, aircraft, submarines and other equipment, becoming an irreplaceable strategic metal material in the fields of aviation, aerospace and navigation. With the continuous improvement of the requirements for alloy performance, titanium alloys have gradually developed towards multi-component and multi-phase systems. Among them, multi-component Ti-Al-Mo-V-Fe alloys are the key alloy systems in high-strength titanium alloys and are also the hot spot for the research of β-type titanium alloys. For example, the typical near-β-type titanium alloy TC18 (Ti-5Al-5Mo-5V-1Cr-1Fe) can reach a tensile strength of more than 1200MPa after strengthening heat treatment, and is mainly used for aircraft load-bearing structures. The Ti1300 (Ti-5Al-4Mo-4V-4Cr-3Zr) near-β-type titanium alloy developed by the Northwest Institute of Nonferrous Metals has achieved a combination of high strength and good ductility on the basis of multi-component strengthening, and can be used as aerospace structural parts for large aircraft. At present, multi-component Ti-Al-Mo-V-Cr based titanium alloy has become an important material for the new generation of aircraft structural components, and has significant strategic needs and development prospects in the aerospace field.

[0003] In industrial production, the organization control method of multi-component titanium alloy is mainly through solidification control, thermal deformation and heat treatment. Patent CN108754373A changes the surface grain morphology of titanium alloy between columnar crystals and equiaxed crystals by adjusting the laser surface melting process parameters, but it cannot achieve precise control of grain size and number. Patents CN114000075A and CN115627430A use multi-fire forging, heat preservation and quenching processes to refine β-Ti grains, but the process steps are cumbersome, time-consuming and costly. Under extraordinary conditions characterized by no container and high vacuum, metal materials can achieve deep supercooling and rapid solidification, thereby significantly improving the organization and performance. However, the solidification process of multi-component titanium alloy is very complicated, involving solute redistribution of multiple elements and multiple phase nucleation and growth processes. At present, there are very limited reports on the preparation of supernormal solidification of multi-component titanium alloys, and it is difficult to achieve precise control of the number and size of grains in the alloy. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for controlling the number and size of multi-component titanium alloy grains in view of the above-mentioned deficiencies of the prior art. The method realizes direct control of the microstructure of the multi-component titanium alloy through multi-component titanium alloy component design and extraordinary solidification, solves the problem that the number and size of grains in the existing multi-component titanium alloy are difficult to accurately control, and does not require subsequent thermal mechanical processing and other processing processes, thereby simplifying the preparation process while optimizing the structure.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for controlling the number and size of multi-element titanium alloy grains, characterized in that the method comprises the following steps:

[0006] Step 1, using high-purity Ti, Al, Mo, V, Fe, Cr metals as raw materials, and preparing the raw materials according to the designed composition of the target product multi-component titanium alloy; the designed composition of the target product multi-component titanium alloy is calculated by mass content: Al 1% to 5%, Mo 1% to 5%, V 1% to 5%, Fe 1% to 25%, Cr 0% to 1%, and the rest is Ti;

[0007] Step 2: preparing a master alloy by high vacuum arc melting the raw materials prepared in step 1, and then crushing the master alloy and preparing a spherical titanium alloy by vacuum laser melting;

[0008] Step 3: placing the spherical titanium alloy prepared in step 2 in an electrostatic suspension system, adjusting the electrostatic field parameters to achieve stable suspension of the spherical titanium alloy, and then controlling the laser heating power to melt and overheat the spherical titanium alloy to obtain an alloy melt;

[0009] Step 4: Under electrostatic suspension conditions, the alloy melt in step 3 is rapidly solidified by controlling the supercooling degree, thereby regulating the number and size of multi-component titanium alloy grains to obtain a multi-component titanium alloy.

[0010] Supercooling will significantly affect the nucleation rate and growth rate of crystals in the alloy melt. When the supercooling increases, the nucleation rate and growth rate of the crystal will increase, and the combined effect of the two determines the final organizational characteristics. For most metal materials, the crystal nucleation rate increases more significantly with the increase of supercooling, so the grain size decreases with the increase of supercooling, and the microstructure is still a polycrystalline material. For some materials, if the crystal growth rate increases more significantly, once the crystal nucleus is formed, it will grow rapidly until the solidification ends, and other crystal nuclei will not have time to form and grow, so the grain size tends to increase, and the microstructure changes from polycrystalline to single crystal material. Based on the above research results, the present invention designs the composition of the multi-crystalline titanium alloy, combines the supernormal solidification technology, and controls the supercooling of the alloy melt for rapid solidification, so as to prepare a multi-crystalline titanium alloy whose grain number and size can be regulated in a large range, without the need for subsequent thermal processing and heat treatment, and effectively shortens the preparation cycle of high-performance titanium alloy.

[0011] The above-mentioned method for controlling the number and size of multi-component titanium alloy grains is characterized in that the mass purity of the high-purity Ti, Al, Mo, V, Fe, and Cr metals described in step one is all above 99.9%.

[0012] The above-mentioned method for controlling the number and size of multi-element titanium alloy grains is characterized in that the mass of the master alloy in step 2 is 300mg to 500mg, and the mass of the spherical titanium alloy is 30mg to 70mg. By controlling the mass range of the master alloy, the lower mass limit is used to ensure the accuracy of weighing low-content elements in the master alloy, and the upper mass limit is used to effectively avoid the segregation of elements such as Fe, Cr, and Mo in large-volume samples, which is conducive to the preparation of spherical titanium alloys with uniform composition. At the same time, by controlling the mass of the spherical titanium alloy, the diameter of the spherical titanium alloy is controlled to be 2.0mm to 3.0mm to ensure the stable suspension of the spherical titanium alloy in the electrostatic field.

[0013] The above-mentioned method for controlling the number and size of multi-component titanium alloy grains is characterized in that the superheat of the alloy melt in step 3 is 10K to 300K. Usually, the vacuum degree in the electrostatic suspension system is controlled to be less than 5×10 -4 Pa.

[0014] The above-mentioned method for controlling the number and size of multi-element titanium alloy grains is characterized in that there is a one-to-one correspondence between the supercooling and the cooling rate of the alloy melt described in step four. For most alloys, there is no corresponding relationship between the supercooling and the cooling rate of the melt, that is, different supercooling can be obtained under one cooling rate condition. Therefore, when performing microstructure control, it is necessary to consider both the cooling rate and the supercooling, and it is difficult to achieve precise control of the number and size of grains. The present invention designs and screens the alloy components so that there is a corresponding relationship between the cooling rate and the supercooling of the melt. Therefore, the supercooling can be determined after the cooling rate is selected, so that precise control of the microstructure can be achieved.

[0015] The above-mentioned method for controlling the number and size of multi-element titanium alloy grains is characterized in that the method for controlling the supercooling of the alloy melt in step four is: controlling the cooling rate of the alloy melt by adjusting the laser heating power, and based on the correspondence between the supercooling of the alloy melt and the cooling rate, allowing the alloy melt to solidify rapidly at a specific supercooling.

[0016] The above-mentioned method for controlling the number and size of multi-component titanium alloy grains is characterized in that the number of grains of the multi-component titanium alloy in step 4 is 1 to 80, and the grain size is 10 μm to 3000 μm.

[0017] The above-mentioned method for regulating the number and size of multi-component titanium alloy grains is characterized in that the method for regulating the number and size of multi-component titanium alloy grains in step 4 is: when the supercooling of the alloy melt is 0-150K, the number of grains of the multi-component titanium alloy is 30-80, and the grain size is 10μm-500μm; when the supercooling of the alloy melt is 180K-250K, the number of grains of the multi-component titanium alloy is 10-29, and the grain size is 50μm-800μm; when the supercooling of the alloy melt is 260K-320K, the number of grains of the multi-component titanium alloy is 2-9, and the grain size is 150μm-2500μm; when the supercooling of the alloy melt is 340K-400K, the number of grains of the multi-component titanium alloy is 1, and the grain size is 2000μm-3000μm.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. The present invention adopts an extraordinary solidification method to control the supercooling of the multi-component titanium alloy melt for rapid solidification, effectively regulate the number and size of the multi-component titanium alloy grains, and realize direct regulation of the microstructure of the multi-component titanium alloy. The structure can be optimized without subsequent complex thermal deformation and heat treatment, effectively shortening the preparation cycle of high-performance titanium alloys and significantly reducing production costs.

[0020] 2. The present invention designs the composition of the multi-component titanium alloy. On the one hand, it makes the grain growth rate in the alloy melt change more obviously with the supercooling degree. On the other hand, it makes the supercooling degree of the alloy melt have a specific corresponding relationship with the cooling rate. Finally, the supercooling degree can be controlled by changing the cooling rate, and then the number of grains can be controlled to 1 to 80, and the grain size can be controlled to 10μm to 3000μm, thereby realizing the precise regulation of the microstructure of the multi-component titanium alloy in a large range.

[0021] 3. The present invention combines high vacuum arc melting with vacuum laser melting. The master alloy is first prepared by high vacuum arc melting, which solves the problem that low-content elements in small batches of master alloys are difficult to directly weigh and mix. The mass range of the master alloy is controlled to reduce the segregation of elements such as Fe, Cr, and Mo. Then, a spherical titanium alloy with uniform chemical composition is prepared by vacuum laser melting.

[0022] 4. The present invention can prepare fine-grained materials with uniform grain shape and size, twin crystal materials containing two grains of identical size, and single crystal materials with consistent orientation through multi-component titanium alloy component design and extraordinary solidification, thereby obtaining multi-component titanium alloy materials with different structures such as fine crystals, twin crystals and single crystals to meet different application requirements.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a cooling curve diagram of the electrostatic suspension process of the multi-component Ti-25Fe-1Al-1Mo-1V-1Cr titanium alloy material in Example 1 of the present invention.

[0025] Figure 2 Graph showing the relationship between the undercooling degree and the cooling rate of the multi-component titanium alloy in Examples 2 and 3 of the present invention.

[0026] Figure 3 This is a microstructure diagram of a multi-component Ti-23Fe-3Al-3Mo-3V titanium alloy material with a polycrystalline structure prepared in Example 2 of the present invention.

[0027] Figure 4 This is a microstructure diagram of a multi-component Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy material with a twin crystal structure prepared in Example 3 of the present invention.

[0028] Figure 5 This is a microstructure diagram of a multi-component Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy material with a single crystal structure prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0029] Example 1

[0030] Step 1, using high-purity Ti, Al, Mo, V, Fe, and Cr metals with a mass purity of 99.9% or more as raw materials, and preparing the raw materials according to the designed composition of the target product multi-component titanium alloy; the designed composition of the target product multi-component titanium alloy is calculated by mass content: Al 1%, Mo 1%, V 1%, Fe 25%, Cr 1%, and the rest is Ti;

[0031] Step 2: 450 mg of the raw material prepared in step 1 is melted by high vacuum arc to prepare a master alloy, and then 51 mg of the master alloy is crushed and melted by vacuum laser to prepare a spherical titanium alloy;

[0032] Step 3: placing the spherical titanium alloy prepared in step 2 in an electrostatic suspension system, adjusting the electrostatic field parameters to achieve stable suspension of the spherical titanium alloy, and then controlling the laser heating power to melt the spherical titanium alloy and overheat it to 277K to obtain an alloy melt;

[0033] Step 4: Under the condition of electrostatic suspension, the cooling rate of the alloy melt is 75K / s by reducing the laser heating power, so that the alloy melt is rapidly solidified at 353K undercooling. The cooling curve is as follows: Figure 1As shown, a multi-component Ti-25Fe-1Al-1Mo-1V-1Cr titanium alloy material with a single crystal structure is prepared; the number of grains in the multi-component Ti-25Fe-1Al-1Mo-1V-1Cr titanium alloy material is 1, and the grain size is 2543 μm.

[0034] Example 2

[0035] This embodiment includes the following steps:

[0036] Step 1: Use high-purity Ti, Al, Mo, V, Fe, and Cr metals with a mass purity of 99.9% or more as raw materials, and prepare the raw materials according to the designed composition of the target product multi-component titanium alloy; the designed composition of the target product multi-component titanium alloy is calculated by mass content: Al 3%, Mo 3%, V 3%, Fe 23%, Cr 0%, and the rest is Ti; the relationship between the supercooling degree and the cooling rate of the multi-component titanium alloy is as follows Figure 2 As shown, there is a linear relationship;

[0037] Step 2: 300 mg of the raw material prepared in step 1 is melted by high vacuum arc to prepare a master alloy, and then 63 mg of the master alloy is crushed and melted by vacuum laser to prepare a spherical titanium alloy;

[0038] Step 3: placing the spherical titanium alloy prepared in step 2 in an electrostatic suspension system, adjusting the electrostatic field parameters to achieve stable suspension of the spherical titanium alloy, and then controlling the laser heating power to melt the spherical titanium alloy and overheat it by 300K to obtain an alloy melt;

[0039] Step 4: Under electrostatic suspension conditions, the cooling rate of the alloy melt is 186K / s by reducing the laser heating power, so that the alloy melt is rapidly solidified at 94K undercooling, and a multi-component Ti-23Fe-3Al-3Mo-3V titanium alloy material with a polycrystalline structure is prepared; the multi-component Ti-23Fe-3Al-3Mo-3V titanium alloy material has 62 grains and a grain size of 10μm to 420μm, such as Figure 3 As shown, the black lines in the figure represent grain boundaries.

[0040] Example 3

[0041] Step 1: Use high-purity Ti, Al, Mo, V, Fe, and Cr metals with a mass purity of more than 99.9% as raw materials, and prepare the raw materials according to the designed composition of the target product multi-component titanium alloy; the designed composition of the target product multi-component titanium alloy is calculated by mass content: Al 5%, Mo 5%, V 5%, Fe 1%, Cr 1%, and the rest is Ti; the relationship between the supercooling degree and the cooling rate of the multi-component titanium alloy is as follows: Figure 2 As shown, there is a linear relationship;

[0042] Step 2: 500 mg of the raw material prepared in step 1 is subjected to high vacuum arc melting to prepare a master alloy, and then the master alloy is crushed and 51 mg is taken out to prepare a spherical titanium alloy by vacuum laser melting;

[0043] Step 3: placing the spherical titanium alloy prepared in step 2 in an electrostatic suspension system, adjusting the electrostatic field parameters to achieve stable suspension of the spherical titanium alloy, and then controlling the laser heating power to melt the spherical titanium alloy and overheat it by 10K to obtain an alloy melt;

[0044] Step 4: Under electrostatic suspension conditions, the cooling rate of the alloy melt is 131K / s by reducing the laser heating power, so that the alloy melt is rapidly solidified at a supercooling degree of 266K, and a multi-component Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy material with a twin crystal structure is prepared; the multi-component Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy material has two grains, and the grain sizes are 1482μm and 1535μm, respectively. Figure 4 shown.

[0045] Example 4

[0046] Step 1: using high-purity Ti, Al, Mo, V, Fe, and Cr metals with a mass purity of 99.9% or more as raw materials, and preparing the raw materials according to the designed composition of the target product multi-component titanium alloy; the designed composition of the target product multi-component titanium alloy is calculated by mass content: Al 5%, Mo 5%, V 5%, Fe 1%, Cr 1%, and the rest is Ti;

[0047] Step 2: 500 mg of the raw material prepared in step 1 is subjected to high vacuum arc melting to prepare a master alloy, and then the master alloy is crushed and 65 mg is taken out to prepare a spherical titanium alloy by vacuum laser melting;

[0048] Step 3: placing the spherical titanium alloy prepared in step 2 in an electrostatic suspension system, adjusting the electrostatic field parameters to achieve stable suspension of the spherical titanium alloy, and then controlling the laser heating power to melt the spherical titanium alloy and overheat it by 40K to obtain an alloy melt;

[0049] Step 4: Under electrostatic suspension conditions, the cooling rate of the alloy melt is 105K / s by reducing the laser heating power, so that the alloy melt is rapidly solidified at a supercooling degree of 363K, and a multi-component Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy material with a single crystal structure is prepared; the multi-component Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy material has one grain and a grain size of 2103μm. Figure 5 shown.

[0050] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for controlling the number and size of multi-component titanium alloy grains, characterized in that: The method comprises the following steps: Step 1, using high-purity Ti, Al, Mo, V, Fe, Cr metals as raw materials, and preparing the raw materials according to the designed composition of the target product multi-component titanium alloy; the designed composition of the target product multi-component titanium alloy is calculated by mass content: Al 1% to 5%, Mo 1% to 5%, V 1% to 5%, Fe 1% to 25%, Cr 0% to 1%, and the rest is Ti; Step 2: preparing a master alloy by high vacuum arc melting the raw materials prepared in step 1, and then crushing the master alloy and preparing a spherical titanium alloy by vacuum laser melting; Step 3: placing the spherical titanium alloy prepared in step 2 in an electrostatic suspension system, adjusting the electrostatic field parameters to achieve stable suspension of the spherical titanium alloy, and then controlling the laser heating power to melt and overheat the spherical titanium alloy to obtain an alloy melt; Step 4: Under electrostatic suspension conditions, the alloy melt in step 3 is rapidly solidified by controlling the supercooling degree, thereby regulating the number and size of multi-component titanium alloy grains to obtain a multi-component titanium alloy.

2. A method for controlling the number and size of multi-component titanium alloy grains according to claim 1, characterized in that: The mass purity of the high-purity Ti, Al, Mo, V, Fe, and Cr metals described in step 1 is all above 99.9%.

3. A method for controlling the number and size of multi-component titanium alloy grains according to claim 1, characterized in that: The mass of the master alloy in step 2 is 300 mg to 500 mg, and the mass of the spherical titanium alloy is 30 mg to 70 mg.

4. A method for controlling the number and size of multi-component titanium alloy grains according to claim 1, characterized in that: The superheat of the alloy melt in step 3 is 10K to 300K.

5. The method for controlling the number and size of multi-component titanium alloy grains according to claim 1, characterized in that: In step 4, there is a one-to-one correspondence between the supercooling degree and the cooling rate of the alloy melt.

6. A method for controlling the number and size of multi-component titanium alloy grains according to claim 1, characterized in that: The method for controlling the supercooling of the alloy melt in step 4 is: controlling the cooling rate of the alloy melt by adjusting the laser heating power, and according to the corresponding relationship between the supercooling of the alloy melt and the cooling rate, allowing the alloy melt to solidify rapidly at a specific supercooling.

7. A method for controlling the number and size of multi-component titanium alloy grains according to claim 1, characterized in that: The number of grains of the multi-component titanium alloy in step 4 is 1 to 80, and the grain size is 10 μm to 3000 μm.

8. The method for controlling the number and size of multi-component titanium alloy grains according to claim 1, characterized in that: The method for regulating the number and size of multi-component titanium alloy grains described in step 4 is: when the supercooling degree of the alloy melt is 0-150K, the number of grains of the multi-component titanium alloy is 30-80, and the grain size is 10μm-500μm; when the supercooling degree of the alloy melt is 180K-250K, the number of grains of the multi-component titanium alloy is 10-29, and the grain size is 50μm-800μm; when the supercooling degree of the alloy melt is 260K-320K, the number of grains of the multi-component titanium alloy is 2-9, and the grain size is 150μm-2500μm; when the supercooling degree of the alloy melt is 340K-400K, the number of grains of the multi-component titanium alloy is 1, and the grain size is 2000μm-3000μm.

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