Heat treatment-liquid nitrogen treatment-cryogenic forging composite forming method for obtaining alpha '+ alpha' biphase martensitic structure titanium alloy

Abstract

The invention aims to provide a heat treatment-liquid nitrogen treatment-cryogenic forging composite forming method for obtaining an alpha '+ alpha' double-phase martensitic structure titanium alloy, and belongs to the technical field of titanium alloy plastic processing and heat treatment. Through liquid nitrogen treatment, the sample obtains a uniform cryogenic temperature and stabilizes an alpha'martensite phase structure; alpha'martensite to alpha '' martensite phase transformation of the alloy is promoted through cryogenic forging. And finally, obtaining the needle-shaped alpha '+ alpha' 'biphase martensitic structure titanium alloy forge piece based on the synergistic effect of heat treatment, liquid nitrogen treatment and cryogenic forging. Compared with traditional cryogenic forming of the titanium alloy, the method can achieve uniform distribution of nanoscale alpha '+ alpha' 'biphase martensite in the titanium alloy forge piece, meanwhile, the technological process is simple, and actual production is easy.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of plastic processing and heat treatment of titanium alloy, and particularly relates to a heat treatment-liquid nitrogen treatment-deep cryogenic forging composite forming method for obtaining alpha prime + alpha double-phase martensite structure titanium alloy. BACKGROUND

[0002] Titanium alloy has more excellent comprehensive performance and broader market prospect compared with traditional cobalt-chromium alloy, stainless steel and other biomedical implant materials. For biomedical implant materials, strength and elasticity are two most critical mechanical performance parameters, and alloys with low elastic modulus, high elasticity and high strength are more suitable for use as human bone implants and dental implant materials. Titanium alloy can be divided into alpha titanium alloy, alpha + beta titanium alloy and beta titanium alloy. Among them, the alpha + beta titanium alloy has high strength, but also has high elastic modulus and poor elasticity. For example, Ti-6Al-4V is the most widely used biomedical titanium alloy material at present, but its high elastic modulus (about 110 GPa) is difficult to meet the performance requirements of advanced biomedical implants, and how to reduce the elastic modulus of alpha + beta titanium alloy is still a difficult problem to solve. On the other hand, beta titanium alloy contains beta phase or alpha '' martensite phase with low elastic modulus, and has lower elastic modulus and higher elasticity compared with alpha + beta titanium alloy. However, the melting point of Mo, Ta, Nb and other alloying elements in beta titanium alloy is too high, causing the alloy to be difficult to smelt, and the prices of these alloying elements are too high, increasing the cost of the alloy. On the other hand, the strength of beta titanium alloy is generally lower than that of alpha + beta titanium alloy, and it has high elasticity and high strength.

[0003] The martensite phase (i.e. alpha'hexagonal martensite and alpha '' tetragonal martensite) in titanium alloy has a significant influence on the mechanical properties of the alloy. The martensite phase transformation of titanium alloy is closely related to the element composition of the alloy, among which alpha'hexagonal martensite is commonly found in quenched alpha titanium alloy and alpha + beta titanium alloy, and alpha '' tetragonal martensite with low elastic modulus mostly appears in quenched or deformed beta titanium alloy. At present, the existing forming processing and heat treatment process is difficult to introduce alpha '' tetragonal martensite in alpha + beta titanium alloy, so it is difficult to reduce the elastic modulus of alpha + beta titanium alloy by introducing alpha '' phase.

[0004] Deep cryogenic forming refers to a method of plastic forming of a workpiece at liquid nitrogen temperature, which has been proved to be able to significantly improve the mechanical properties of alloys. At present, the reports on deep cryogenic forming of titanium alloys are mostly focused on refining the grain size of the alloy, homogenizing the structure, and improving the strength and plasticity of the alloy. There is no report on deep cryogenic forming of alpha prime martensite structure titanium alloy to obtain alpha prime plus alpha double phase martensite structure titanium alloy. The publication CN116274592A relates to a low-temperature superplastic forming method of TC4 titanium alloy sheet, which specifically includes liquid nitrogen soaking and deep cryogenic rolling processes. The publication CN119702753A relates to a short process preparation method of high strength and plasticity titanium plate, which obtains titanium plate with excellent strength and plasticity through high temperature forging breakdown, hot rolling, deep cryogenic rolling and other processes. The publication CN118291900A relates to a titanium material based on mixed crystal and twin crystal synergistic strength and plasticity and a preparation method thereof, which obtains a mixed crystal and twin crystal structure through hot rolling breakdown, multi-pass cold rolling, annealing, deep cryogenic rolling and partial recrystallization annealing. The structure can improve the strength and plasticity matching performance of the titanium material and has excellent strength and work hardening capacity. The publication CN109518107A relates to a deep cryogenic rolling and heat treatment preparation method of high-performance titanium strip. The obtained titanium strip has higher strength and toughness than the material prepared by cold rolling. Although the above processes can improve the strength and plasticity of titanium alloy, they cannot obtain titanium alloy with alpha prime plus alpha double phase martensite structure. SUMMARY

[0005] The present application provides a heat treatment-liquid nitrogen treatment-deep cryogenic forging composite forming method for obtaining alpha prime plus alpha double phase martensite structure titanium alloy to solve the problems in the prior art. The titanium alloy forgings prepared by the method contain alpha prime hexagonal martensite and alpha double phase tetragonal martensite. The method is simple and easy to implement and promote industrial production.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: A heat treatment-liquid nitrogen treatment-deep cryogenic forging composite forming method for obtaining alpha prime plus alpha double phase martensite structure titanium alloy, comprising the following steps: S1, selecting an alpha plus beta type titanium alloy blank as a raw material, heating and holding the titanium alloy blank, and then water cooling the titanium alloy blank to room temperature to obtain an alpha prime martensite phase structure; S2, welding an R-type thermocouple at the center of the side of the sample after heat treatment, and then quenching into liquid nitrogen and holding in liquid nitrogen to obtain uniform temperature distribution; S3, deep cryogenic forging the titanium alloy sample in a liquid nitrogen atmosphere to promote the phase transition of the alloy from alpha prime martensite to alpha double phase martensite. After forging, the forgings are slowly restored to room temperature in a room temperature environment.

[0007] Further, the titanium alloy blank in S1 is heated to a temperature interval of 30 DEG C above the phase transition point to 30 DEG C below the phase transition point, and is kept for 15-30 min.

[0008] Further, the keeping time in the liquid nitrogen in S2 is 30-60 min.

[0009] Further, the deformation rate of the cryogenic forging in S3 is 0.001 / s to 0.1 / s, and the deformation amount is 10%-50%.

[0010] In the above process, the purpose of the heat treatment and water quenching is to obtain a needle-shaped α' martensite phase titanium alloy; the purpose of the liquid nitrogen treatment is to make the sample obtain a uniform cryogenic temperature and stabilize the α' martensite phase; the purpose of the cryogenic forging is to promote the phase transition of the alloy from α' martensite to α'' martensite. Finally, based on the synergistic effect of the heat treatment-liquid nitrogen treatment-cryogenic forging, a needle-shaped α'+α'' dual-phase martensite titanium alloy forging is obtained.

[0011] The beneficial effects of the present application are as follows: 1. It is difficult for the traditional forming processing and heat treatment process to introduce α'' tetragonal martensite into the α+β titanium alloy, and the present application promotes the phase transition of the alloy from α' martensite to α'' martensite through cryogenic forging, thereby successfully introducing α'' tetragonal martensite into the α+β titanium alloy, and obtaining an α'+α'' dual-phase martensite titanium alloy forging.

[0012] 2. The α'+α'' dual-phase martensite structure obtained in the α+β titanium alloy has a nanoscale grain size, while the traditional forming and heat treatment process for obtaining nanocrystalline titanium alloy is relatively complex, and the present application can be completed through a three-stage composite process of heat treatment-liquid nitrogen treatment-cryogenic forging, which requires simple equipment and does not need expensive molds. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 The process flowchart of the present application.

[0014] Figure 2 The microstructure photo of the nanoscale α'+α'' dual-phase martensite Ti-6Al-4V titanium alloy forging prepared in Example 1 of the present application.

[0015] Figure 3 The microstructure photo of the nanoscale α'+α'' dual-phase martensite Ti-6Al-4V titanium alloy forging prepared in Example 2 of the present application. DETAILED DESCRIPTION

[0016] In order to make the purposes, technical solutions and advantages of the present application more clear, the specific embodiments of the present application are described in detail, but not limited to. The raw materials used in the embodiments are ordinary commercially available products unless otherwise specified; the methods used are common methods in the art unless otherwise specified.

[0017] A heat treatment-liquid nitrogen treatment-cryogenic forging composite forming method for obtaining an α'+α" two-phase martensite structure titanium alloy, comprising the following steps: S1, selecting an α+β type titanium alloy blank as a raw material, heating and holding the titanium alloy blank, and then water cooling the titanium alloy blank to room temperature to obtain an α' martensite phase structure; S2, welding an R-type thermocouple at the center of the side of the sample after heat treatment, then quenching into liquid nitrogen, and holding in liquid nitrogen to obtain uniform temperature distribution; S3, cryogenic forging the titanium alloy sample under liquid nitrogen atmosphere to promote the phase transition of the alloy from α' martensite to α'' martensite, and then slowly recovering the forged piece to room temperature in a room temperature environment after forging, and obtaining the titanium alloy with α'+α" two-phase martensite structure.

[0018] Further, the titanium alloy blank in S1 is heated to a temperature interval of 30 ℃ above the phase transition point to 30 ℃ below the phase transition point, and held for 15-30 min.

[0019] Further, the holding time in liquid nitrogen in S2 is 30-60 min.

[0020] Further, the deformation rate of the cryogenic forging in S3 is 0.001 / s to 0.1 / s, and the deformation amount is 10%-50%.

[0021] Example 1 The raw material used in this embodiment is a typical α+β type titanium alloy, Ti-6Al-4V, and the phase transition temperature (T β ) of the alloy is about 990℃. The specific process of this embodiment is as follows: Step one, heat the Ti-6Al-4V titanium alloy blank (sample 1) to 1020℃ (T β +30℃) at a heating rate of 10℃ / s, then hold at 1020℃ for 15 min to obtain uniform structure, and then water cool the titanium alloy blank to room temperature after holding.

[0022] Step two, weld an R-type thermocouple at the center of the side of the sample after heat treatment, then quench into liquid nitrogen, and hold in liquid nitrogen for 30 min to obtain uniform temperature distribution.

[0023] Step 3: In liquid nitrogen atmosphere, the titanium alloy sample is cryogenically forged, wherein the deformation rate is 0.04 / s and the deformation amount is 35%. After forging, the forging is placed in a room temperature environment and slowly restored to room temperature. Figure 2 shown.

[0024] Depend on Figure 2 It can be seen that the forged sample is composed of dark gray needle-shaped α″ martensite and light gray needle-shaped α′ martensite, and a nanoscale α′+α″ dual-phase martensite structure is obtained.

[0025] Example 2 The raw material used in this example is a typical α+β type titanium alloy, Ti-6Al-4V, and the phase transition temperature (T β ) is about 990°C. The specific process of this embodiment is as follows: Step 1: Heat the Ti-6Al-4V titanium alloy blank (sample 2) to 1020°C (T β +30℃), the heating rate was 10℃ / s, and then the titanium alloy billet was kept at 1020℃ for 15 min to obtain a uniform structure. After the holding period, the titanium alloy billet was water-cooled to room temperature.

[0026] Step 2: Weld an R-type thermocouple to the center of the side of the heat-treated sample, then quench it into liquid nitrogen and keep it in liquid nitrogen for 30 minutes to obtain a uniform temperature distribution.

[0027] Step 3: In liquid nitrogen atmosphere, the titanium alloy sample is cryogenically forged with a deformation rate of 0.04 / s and a deformation amount of 10%. After forging, the forging is placed in a room temperature environment and slowly restored to room temperature. Figure 3 shown.

[0028] Depend on Figure 3 It can be seen that the forged sample is composed of dark gray needle-shaped α″ martensite and light gray needle-shaped α′ martensite, and a nanoscale α′+α″ dual-phase martensite structure is obtained.

[0029] The technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application. The description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all fall within the scope of protection of the present application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.

Claims

1. A heat treatment-liquid nitrogen treatment-cold forging composite forming method for obtaining an α′+α″ dual-phase martensitic titanium alloy, characterized by: The steps include: S1. Selecting an α+β titanium alloy billet as a raw material, heating and keeping the titanium alloy billet warm, and then water-cooling the titanium alloy billet to room temperature to obtain an α′ martensite phase structure; S2. Weld an R-type thermocouple to the center of the side of the heat-treated sample, then quench it into liquid nitrogen and keep it in liquid nitrogen to obtain a uniform temperature distribution; S3. In a liquid nitrogen atmosphere, the titanium alloy sample is cryogenically forged to induce a phase transformation from α′ martensite to α′′ martensite in the alloy. After forging, the forging is placed in a room temperature environment and slowly restored to room temperature.

2. The heat treatment-liquid nitrogen treatment-cold forging composite forming method for obtaining an α′+α″ dual-phase martensitic titanium alloy according to claim 1, characterized in that: The titanium alloy billet described in S1 is heated to a temperature range of 30°C above the phase transformation point to 30°C below the phase transformation point, and is kept at this temperature for 15-30 minutes.

3. The heat treatment-liquid nitrogen treatment-cold forging composite forming method for obtaining an α′+α″ dual-phase martensitic titanium alloy according to claim 1, characterized in that: The holding time in liquid nitrogen in S2 is 30-60 min.

4. The heat treatment-liquid nitrogen treatment-cold forging composite forming method for obtaining an α′+α″ dual-phase martensitic titanium alloy according to claim 1, characterized in that: The deformation rate of the deep cold forging in S3 is 0.001 / s to 0.1 / s, and the deformation amount is 10%-50%.

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