A processing technology for improving mechanical properties of Ti-Al-V-Cr-Fe system low-cost titanium alloy

Abstract

This invention discloses a processing technology to improve the mechanical properties of low-cost Ti-Al-V-Cr-Fe titanium alloys. The process includes: 1. performing multi-stage forging and high-temperature forging of the titanium alloy ingot above its phase transformation temperature; 2. forging below its phase transformation temperature; 3. final forging above its phase transformation temperature; and 4. annealing followed by air cooling to room temperature to obtain the Ti-Al-V-Cr-Fe titanium alloy. This invention employs a high-low-high forging method, combined with post-forging air cooling and water cooling, and annealing, to obtain a complex microstructure with necklace-like grain boundary α phases and basket-like multi-scale lamellar α phases. This results in a finished titanium alloy with high strength, good plasticity, and toughness, significantly improving the overall strength-plasticity-toughness performance of the titanium alloy.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy technology, specifically relating to a processing technology for improving the mechanical properties of low-cost titanium alloys based on the Ti-Al-V-Cr-Fe system. Background Technology

[0002] Titanium and titanium alloys are widely used in the marine field due to their excellent comprehensive properties, such as low density, high specific strength, corrosion resistance, high temperature resistance, non-magnetic properties, and good weldability. With the increasing use of titanium alloys in the marine field, there is an urgent need to develop low-cost titanium alloys and research their preparation technologies. To vigorously develop high-reliability and long-life titanium alloy products, titanium alloys for key structural components must possess superior strength-toughness matching and damage resistance. Currently, the Northwest Nonferrous Metals Research Institute, considering the reduction of raw material costs and the recycling of recycled materials, has designed a novel Ti-Al-V-Cr-Fe low-cost titanium alloy by controlling the alloy composition and content. Researching the processing and preparation technology of this low-cost titanium alloy to achieve a good match of its mechanical properties, expand its application range in the marine field, and increase its usage and application level in the marine sector is urgently needed.

[0003] The mechanical properties of titanium alloys depend on their microstructure, which in turn is closely related to processing techniques. Studies have shown that the size, volume fraction, and location distribution of the α phase in titanium alloys significantly affect their mechanical properties. Equiaxed α phases exhibit excellent deformation-coordinating capabilities, which is beneficial for improving plasticity. Lamellar α phases effectively hinder crack propagation, thus improving fracture toughness; however, continuously distributed lamellar α phases at β grain boundaries easily induce intergranular crack propagation, significantly reducing fracture toughness. The fineness of the intragranular lamellar α phases also has a significant impact on strength; finer lamellars result in higher strength. Therefore, controlling the precipitation behavior of the α phase through appropriate processing methods to construct multi-level precipitates / multi-layered microstructures helps to obtain high-performance, low-cost titanium alloys with good strength-plasticity-toughness matching.

[0004] Chinese invention patent application number 202311569275.2, entitled "A Method for Preparing Large-Size Ti60 Titanium Alloy Bars," obtains a uniform microstructure in both the core and edges through a high-low-high-low forging process combined with water cooling and recrystallization β heat treatment; however, this method is not effective in improving the balance of strength, plasticity, and toughness. Chinese invention patent application number 202311209252.0, entitled "A Forging Method for Improving the Strength-Toughness Matching of TC21 Titanium Alloy," obtains an intermediate billet through quasi-β forging, followed by two-phase forging. Compared to the traditional quasi-β forging process, the strength level of the obtained TC21 titanium alloy is increased by 30 MPa to 60 MPa, but the fracture toughness is reduced by 5 MPa·m. 1 / 2 ~8MPa·m 1 / 2This method also failed to simultaneously improve the strength and toughness mechanical properties. Therefore, obtaining a uniform microstructure by changing the forging process in existing technologies cannot improve the overall mechanical properties of titanium alloys. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a processing technology to improve the mechanical properties of low-cost Ti-Al-V-Cr-Fe titanium alloys. This process employs a high-low-high forging method, combined with post-forging air cooling and water cooling, and annealing, to obtain a complex microstructure with necklace-like grain boundary α phases and basket-like multi-scale lamellar α phases. This significantly improves the overall strength, plasticity, and toughness of the titanium alloy, solving the problem of poor performance matching.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a processing technology for improving the mechanical properties of low-cost titanium alloys based on the Ti-Al-V-Cr-Fe system, characterized in that the process includes the following steps:

[0007] Step 1: The Ti-Al-V-Cr-Fe titanium alloy ingot is subjected to multiple rounds of forging and high-temperature forging above the phase transformation point temperature. The forging and high-temperature forging process involves three upsetting and three drawing operations. Then, it is air-cooled to room temperature to obtain a titanium alloy forging.

[0008] Step 2: Forge the primary titanium alloy forging obtained in Step 1 below the phase transformation point temperature, and perform three upsetting and three drawing processes during the forging process. Then air cool it to room temperature to obtain the secondary titanium alloy forging.

[0009] Step 3: Perform final forging on the secondary titanium alloy forging obtained in Step 2 above the phase transformation point temperature, and perform three upsetting and three drawing processes during the final forging process. Then, cool it to room temperature using a combination of air cooling and water cooling to obtain the tertiary titanium alloy forging.

[0010] Step 4: Anneal the titanium alloy forgings obtained in Step 3, and then air-cool them to room temperature to obtain a Ti-Al-V-Cr-Fe titanium alloy. The Ti-Al-V-Cr-Fe titanium alloy has a tensile strength greater than 1100 MPa, a yield strength greater than 1000 MPa, an elongation greater than 10%, and a fracture toughness K0. IC Greater than 100 MPa·m 1 / 2 .

[0011] The above-mentioned processing technology for improving the mechanical properties of low-cost Ti-Al-V-Cr-Fe titanium alloys is characterized in that the temperature of billet preparation and high-temperature forging in step one is 60℃ to 210℃ above the phase transformation point temperature, and the holding time for each heat treatment is t1 = (d1×0.6+23) min to (d1×0.6+30) min, where d1 is the cross-sectional diameter of the Ti-Al-V-Cr-Fe titanium alloy ingot in mm.

[0012] The aforementioned processing technology for improving the mechanical properties of low-cost Ti-Al-V-Cr-Fe titanium alloys is characterized by the following: in step two, the forging temperature is 20°C to 50°C below the phase transformation temperature, and the holding time is t2 = (d2 × 0.6 + 23) min to (d2 × 0.6 + 30) min, where d2 is the cross-sectional diameter of the titanium alloy forging in mm. The forging temperature and holding time selected in this invention effectively refine the grains, avoiding the problem of difficulty in obtaining uniformly refined equiaxed α grains when the forging temperature is above 20°C below the phase transformation temperature, and the problem of easy cracking of titanium alloys when the forging temperature is below 50°C below the phase transformation temperature.

[0013] The aforementioned processing technology for improving the mechanical properties of low-cost Ti-Al-V-Cr-Fe titanium alloys is characterized by the following: in step three, the final forging temperature is 10°C to 50°C above the phase transformation temperature, and the holding time is t3 = (d3 × 0.6 + 23) min to (d3 × 0.6 + 30) min, where d3 is the cross-sectional diameter of the secondary titanium alloy forging in mm. This invention combines phase transformation and deformation by controlling the final forging temperature and holding time, thus constructing the microstructure. This avoids the problem of excessively large β grains when the final forging temperature is 50°C above the phase transformation temperature, which is detrimental to strength improvement, and the problem of excessive equiaxed α grains forming during the cooling process of the titanium alloy when the final forging temperature is 10°C below the phase transformation temperature, which is detrimental to fracture toughness improvement.

[0014] The aforementioned processing technology for improving the mechanical properties of low-cost Ti-Al-V-Cr-Fe titanium alloys is characterized by the following cooling method in step three: first air cooling to 680℃~710℃, then water cooling to room temperature. This invention supplements the grain refinement process by controlling the cooling method after forging. Air cooling to 680℃~710℃ first effectively controls the size and content of the secondary coarse α phase after forging, avoiding the problem of excessively high content of the secondary coarse α phase after forging due to air cooling below 680℃, and the problem of excessively low content of the secondary coarse α phase after forging due to air cooling above 710℃, which is detrimental to the release of internal stress in the alloy. Then, water cooling is performed after air cooling to increase the degree of supercooling, increase the number of crystal nuclei, and provide a driving force for the phase transformation in subsequent annealing heat treatment. This provides a large number of crystal nuclei for the transformation of martensite into strip-shaped α phase, changing the precipitation mechanism of the β phase (i.e., from induced nucleation under air cooling conditions to independent nucleation).

[0015] The aforementioned processing technology for improving the mechanical properties of low-cost Ti-Al-V-Cr-Fe titanium alloys is characterized by the annealing temperature in step four being 880℃~910℃ and the holding time being 1h~2h. This invention, through high-temperature annealing with the above parameters, effectively eliminates the internal stress generated during post-forging water cooling, promotes the transformation of martensite α phase to fine strip-shaped α phase, improves mechanical properties, and avoids the problems of annealing temperatures above 910℃ and holding times above 2h resulting in large strip-shaped α phase sizes that cannot guarantee the strength of the titanium alloy, and annealing temperatures below 880℃ and holding times below 1h resulting in the inability to completely eliminate internal stress in the titanium alloy.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. This invention employs a high-low-high forging method, combined with post-forging air cooling + water cooling and annealing, to obtain a complex microstructure of multi-scale lamellar α-phase with necklace-like grain boundary α-phase and basket-like distribution. This results in a titanium alloy with a tensile strength greater than 1100 MPa, a yield strength greater than 1000 MPa, an elongation greater than 10%, and a fracture toughness K0. IC Greater than 100 MPa·m 1 / 2 This breakthrough overcomes the limitation of poorly matching the strength, plasticity, and toughness of titanium alloys, and meets the application requirements of high-performance, low-cost titanium alloys.

[0018] 2. By limiting the final forging temperature to 10°C to 50°C above the phase transformation point, this invention effectively controls the β grain size in the finished titanium alloy. Combined with the "air cooling + water cooling" cooling process after final forging, it effectively suppresses the precipitation and growth of secondary intragranular α phase. Furthermore, needle-like α precipitates at the β grain boundaries, resulting in a necklace-like distribution of α at the grain boundaries after subsequent annealing. The intragranular α lamellae are uneven in size and tightly interwoven, leading to better mechanical properties of the finished titanium alloy.

[0019] 3. The processing technology of this invention is easy to implement and can be widely applied to the processing and preparation of two-phase titanium alloys, with high practical value.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 The image shows the microstructure (50×) of the tertiary titanium alloy forging prepared in Example 1 of this invention.

[0022] Figure 2 Microstructure (200×) of the Ti-5.88Al-3.92V-1Cr-1Fe titanium alloy prepared in Example 1 of this invention. Detailed Implementation

[0023] Example 1

[0024] This embodiment includes the following steps:

[0025] Step 1: The Ti-5.88Al-3.92V-1Cr-1Fe titanium alloy ingot with a cross-sectional diameter d1 = 180 mm is subjected to three-stage forging and high-temperature forging above the phase transformation point temperature. The holding temperature for the first forging is 1150℃, the holding temperature for the second forging is 1050℃, and the holding temperature for the third forging is 1000℃. The holding time for each forging is t1 = 131 min. Each forging process involves three upsetting and three drawing operations. Then, it is air-cooled to room temperature to obtain a primary titanium alloy forging with a cross-sectional diameter d2 = 150 mm.

[0026] Step 2: Forge the primary titanium alloy forging obtained in Step 1. The forging holding temperature is 920℃, the holding time is t2=113min, and the forging process involves three upsetting and three drawing. Then, air cool to room temperature to obtain a secondary titanium alloy forging with a cross-sectional diameter d3=150mm.

[0027] Step 3: Perform final forging on the secondary titanium alloy forging obtained in Step 2. The holding temperature for final forging is 950℃, and the holding time is t3 = 113 min. The final forging process involves three upsetting and three drawing operations. Then, the forging is first air-cooled to 680℃ and then water-cooled to room temperature to obtain the tertiary titanium alloy forging.

[0028] Step 4: Anneal the titanium alloy forgings obtained in Step 3, and then air-cool them to room temperature to obtain Ti-5.88Al-3.92V-1Cr-1Fe titanium alloy; the annealing temperature is 880℃, and the holding time is 1h; the tensile strength of the Ti-5.88Al-3.92V-1Cr-1Fe titanium alloy is greater than 1100MPa, the yield strength is greater than 1000MPa, the elongation is greater than 10%, and the fracture toughness K IC Greater than 100 MPa·m 1 / 2 .

[0029] Figure 1 The image shows the microstructure (50×) of the tertiary titanium alloy forging prepared in this embodiment. Figure 1 It can be seen that the microstructure of the tertiary titanium alloy forging prepared by the forging process of this embodiment consists of elongated β grains parallel to the drawing direction and α plates of varying sizes. The β grains are very uneven in size, ranging from 200μm to 700μm. There are a large number of grain boundary α phases at the grain boundaries of the elongated β grains, and there are many α plates of varying sizes inside the grains. These are nucleated and grown during the air cooling + water cooling process after forging.

[0030] Figure 2 The image shows the microstructure (200×) of the Ti-5.88Al-3.92V-1Cr-1Fe titanium alloy prepared in this embodiment. Figure 2 It can be seen that the Ti-5.88Al-3.92V-1Cr-1Fe titanium alloy prepared by the forging process and annealing treatment in this embodiment is composed of elongated β grains, discontinuous grain boundaries α, and intragranular α with an uneven basket-like structure. It belongs to a multi-scale lamellar structure, thus the Ti-5.88Al-3.92V-1Cr-1Fe alloy has high strength and good plasticity and toughness.

[0031] Example 2

[0032] This embodiment includes the following steps:

[0033] Step 1: The Ti-5.88Al-3.92V-1Cr-1Fe titanium alloy ingot with a cross-sectional diameter d1 = 180 mm is subjected to three-stage forging and high-temperature forging above the phase transformation point temperature. The holding temperature for the first forging is 1150℃, the holding temperature for the second forging is 1050℃, and the holding temperature for the third forging is 1000℃. The holding time for each forging is t1 = 138 min. Each forging process involves three upsetting and three drawing operations. Then, it is air-cooled to room temperature to obtain a primary titanium alloy forging with a cross-sectional diameter d2 = 150 mm.

[0034] Step 2: Forge the primary titanium alloy forging obtained in Step 1. The forging holding temperature is 890℃, the holding time is t2=120min, and the forging process involves three upsetting and three drawing. Then, air cool to room temperature to obtain a secondary titanium alloy forging with a cross-sectional diameter d3=150mm.

[0035] Step 3: Perform final forging on the secondary titanium alloy forging obtained in Step 2. The holding temperature for final forging is 990℃, and the holding time is t3 = 120 min. The final forging process involves three upsetting and three drawing operations. Then, the forging is first air-cooled to 710℃ and then water-cooled to room temperature to obtain the tertiary titanium alloy forging.

[0036] Step 4: Anneal the titanium alloy forgings obtained in Step 3, and then air-cool them to room temperature to obtain Ti-5.88Al-3.92V-1Cr-1Fe titanium alloy; the annealing temperature is 910℃, and the holding time is 2h; the tensile strength of the Ti-5.88Al-3.92V-1Cr-1Fe titanium alloy is greater than 1100MPa, the yield strength is greater than 1000MPa, the elongation is greater than 10%, and the fracture toughness K IC Greater than 100 MPa·m 1 / 2 .

[0037] Upon testing, the microstructure of the tertiary titanium alloy forgings prepared using the forging process of this embodiment consists of elongated β grains parallel to the drawing direction and α plates of varying sizes. The β grains are highly uneven in size, ranging from 200 μm to 500 μm. Furthermore, a large number of grain boundary α phases are present at the grain boundaries of the elongated β grains, and many α plates of varying sizes are present inside the grains. These α plates are nucleated and grown during the air cooling and water cooling process after forging.

[0038] Testing revealed that the Ti-5.88Al-3.92V-1Cr-1Fe titanium alloy prepared using the forging process and annealing treatment described in this embodiment consists of elongated β grains, discontinuous grain boundaries α, clustered domain structures of varying sizes, and intragranular α structures with uneven coarseness and fineness. This results in a multi-layered lamellar structure, giving the Ti-5.88Al-3.92V-1Cr-1Fe alloy high strength, good plasticity, and toughness.

[0039] Example 3

[0040] This embodiment includes the following steps:

[0041] Step 1: The Ti-5.88Al-3.92V-1Cr-1Fe titanium alloy ingot with a cross-sectional diameter d1 = 180 mm is subjected to three-stage forging and high-temperature forging above the phase transformation point temperature. The holding temperature for the first forging is 1150℃, the holding temperature for the second forging is 1050℃, and the holding temperature for the third forging is 1000℃. The holding time for each forging is t1 = 136 min. Each forging process involves three upsetting and three drawing operations. Then, it is air-cooled to room temperature to obtain a primary titanium alloy forging with a cross-sectional diameter d2 = 150 mm.

[0042] Step 2: Forge the primary titanium alloy forging obtained in Step 1. The forging holding temperature is 900℃, the holding time is t2=118min, and the forging process involves three upsetting and three drawing. Then, air cool to room temperature to obtain a secondary titanium alloy forging with a cross-sectional diameter d3=150mm.

[0043] Step 3: Perform final forging on the secondary titanium alloy forging obtained in Step 2. The holding temperature for final forging is 970℃, and the holding time is t3 = 116 min. The final forging process involves three upsetting and three drawing operations. Then, the forging is first air-cooled to 700℃ and then water-cooled to room temperature to obtain the tertiary titanium alloy forging.

[0044] Step 4: Anneal the titanium alloy forgings obtained in Step 3, and then air-cool them to room temperature to obtain Ti-5.88Al-3.92V-1Cr-1Fe titanium alloy; the annealing temperature is 900℃, and the holding time is 1.5h; the tensile strength of the Ti-5.88Al-3.92V-1Cr-1Fe titanium alloy is greater than 1100MPa, the yield strength is greater than 1000MPa, the elongation is greater than 10%, and the fracture toughness K IC Greater than 100 MPa·m 1 / 2 .

[0045] Upon testing, the microstructure of the tertiary titanium alloy forgings prepared using the forging process of this embodiment consists of elongated β grains parallel to the drawing direction and α plates of varying sizes. The β grains are highly uneven in size, ranging from 200 μm to 500 μm. Furthermore, a large number of grain boundary α phases are present at the grain boundaries of the elongated β grains, and many α plates of varying sizes are present inside the grains. These α plates are nucleated and grown during the air cooling and water cooling process after forging.

[0046] Testing revealed that the Ti-5.88Al-3.92V-1Cr-1Fe titanium alloy prepared using the forging process and annealing treatment described in this embodiment consists of elongated β grains, discontinuous grain boundaries α, clustered domain structures of varying sizes, and intragranular α structures with uneven coarseness and fineness. This results in a multi-layered lamellar structure, giving the Ti-5.88Al-3.92V-1Cr-1Fe alloy high strength, good plasticity, and toughness.

[0047] The mechanical properties of the Ti-5.88Al-3.92V-1Cr-1Fe titanium alloys prepared by forging and annealing in Examples 1-3 of this invention were tested, and the results are shown in Table 1 below.

[0048] Table 1

[0049]

[0050]

[0051] As shown in Table 1, the Ti-5.88Al-3.92V-1Cr-1Fe alloys obtained after forging and annealing according to the present invention all have high strength, good plasticity and toughness, and this performance matching is at a high level in the field of titanium alloys.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A processing technology for improving the mechanical properties of low-cost titanium alloys based on the Ti-Al-V-Cr-Fe system, characterized in that, The process includes the following steps: Step 1: The Ti-Al-V-Cr-Fe titanium alloy ingot is subjected to multiple rounds of forging and high-temperature forging above the phase transformation point temperature. The forging and high-temperature forging process involves three upsetting and three drawing operations. Then, it is air-cooled to room temperature to obtain a titanium alloy forging. Step 2: Forge the primary titanium alloy forging obtained in Step 1 below the phase transformation point temperature, and perform three upsetting and three drawing processes during the forging process. Then air cool to room temperature to obtain the secondary titanium alloy forging. Step 3: Perform final forging on the secondary titanium alloy forging obtained in Step 2 above the phase transformation point temperature, and the final forging process involves three upsetting and three drawing operations. Then, cool it to room temperature using a combination of air cooling and water cooling to obtain the tertiary titanium alloy forging. The cooling method is as follows: first air cooling to 680℃~710℃, and then water cooling to room temperature. Step 4: Anneal the titanium alloy forgings obtained in Step 3, and then air-cool them to room temperature to obtain a Ti-Al-V-Cr-Fe titanium alloy. The annealing temperature is 880℃~910℃, and the holding time is 1h~2h. The tensile strength of the Ti-Al-V-Cr-Fe titanium alloy is greater than 1100MPa, the yield strength is greater than 1000MPa, the elongation is greater than 10%, and the fracture toughness K... IC Greater than 100 MPa·m 1 / 2 .

2. The processing technology for improving the mechanical properties of low-cost Ti-Al-V-Cr-Fe titanium alloys according to claim 1, characterized in that, The temperature for billet preparation and high-temperature forging in step one is 60℃~210℃ above the phase transformation point temperature, and the holding time for each heat treatment is t1=(d1×0.6+23)min~(d1×0.6+30)min, where d1 is the cross-sectional diameter of the Ti-Al-V-Cr-Fe titanium alloy ingot, in mm.

3. The processing technology for improving the mechanical properties of low-cost Ti-Al-V-Cr-Fe titanium alloys according to claim 1, characterized in that, The forging temperature in step two is 20℃~50℃ below the phase transformation point temperature, and the holding time is t2=(d2×0.6+23)min~(d2×0.6+30)min, where d2 is the cross-sectional diameter of the titanium alloy forging in one step, in mm.

4. The processing technology for improving the mechanical properties of low-cost Ti-Al-V-Cr-Fe titanium alloys according to claim 1, characterized in that, The final forging temperature mentioned in step three is 10℃~50℃ above the phase transformation point temperature, and the holding time is t3=(d3×0.6+23)min~(d3×0.6+30)min, where d3 is the cross-sectional diameter of the secondary titanium alloy forging in mm.

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