A method for eliminating stress-induced phase transformation during the preparation of diffusion couples in Ti-V-Mo alloys

Abstract

This invention discloses a method for eliminating stress-induced phase transformation during the preparation of diffusion couples in Ti-V-Mo alloys, belonging to the field of titanium alloy diffusion technology. This invention utilizes spark plasma sintering technology, selecting appropriate process parameters to prepare diffusion couples with both ends being single-phase, exhibiting good adhesion and free from stress-induced phase transformation. On the one hand, this invention allows for the preparation of diffusion couples that meet experimental requirements by adjusting process parameters, thus effectively facilitating subsequent experimental research and avoiding blindly setting experimental parameters. On the other hand, it allows for precise control, greatly reducing experimental failures caused by inaccurate parameter control during fixture preparation. This invention enables the preparation of diffusion couples that conform to diffusion concentration gradient experiments, which can then be used for subsequent electron probe microanalysis to further solve for the diffusion coefficient, facilitating the establishment of a titanium alloy diffusion kinetics database.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy diffusion technology, specifically relating to a method for eliminating stress-induced phase transformation during the preparation of Ti-V-Mo alloy diffusion couples. Background Technology

[0002] Ti-V-Mo alloys are widely used in aerospace, shipbuilding, and industrial fields due to their low density, high specific strength, and excellent comprehensive mechanical properties. Compared to Ti-6Al-4V, they exhibit better ballistic resistance under high-speed projectile penetration conditions, while also possessing good room-temperature and dynamic mechanical properties, making them promising for applications in titanium alloy armor plates. However, traditional experiments for the microstructure control and heat treatment processes of Ti-V-Mo alloys are typically time-consuming, inefficient, costly, and yield limited systematic research results. They are not only time-consuming and labor-intensive but may also only be applicable to a single alloy. With the continuous development of computational materials science, scientists have begun to use computer simulations to understand and predict the phase behavior of metallic alloys, replacing traditional experimental observations. CALPHAD (CALculation of PHAse Diagram), as a commonly used computational materials research method, has been widely applied in materials science, especially in the design and optimization of metallic alloys. With the development and advancement of the CALPHAD method, diffusion kinetics has attracted increasing attention. Establishing a corresponding database can not only effectively simulate various diffusion processes quantitatively, but also simulate various diffusion reaction processes such as alloy homogenization, intermediate phase growth and dissolution, which plays a crucial role in material development, design and preparation processes.

[0003] Diffusion kinetics databases can be used for quantitative simulation of various diffusion processes in alloys, including homogenization, mesophase growth, and dissolution. They play a crucial role in material development, design, and fabrication. For titanium alloys, heat treatment is typically performed in the β single-phase region, thus requiring the establishment of a diffusion kinetics database for the bcc single-phase region. During database development, preparing diffusion couples and measuring their composition-distance curves are essential experimental steps. During preparation, the materials are unstable; with low applied forces, alloy samples cannot bond together, resulting in gaps at the interface and a lack of diffusion. With high applied forces, stress-induced martensitic transformation easily occurs, leading to a phase transformation at the diffusion couple interface, thus deviating from the bcc single-phase region and failing to accurately characterize diffusion behavior in the β single-phase region, hindering the establishment of an accurate atomic mobility parameter database. Therefore, it is necessary to prepare diffusion couples with different compositions at both ends of the interface, both being single-phase and free from stress-induced phase transformation. Summary of the Invention

[0004] To address the shortcomings of the existing technology, this invention provides a method for eliminating stress-induced phase transformation during the preparation of Ti-V-Mo alloy diffusion couples, resulting in diffusion couples with both ends being single-phase, exhibiting good adhesion, and free from stress-induced phase transformation. To achieve the above objective, the technical solution adopted by this invention is as follows:

[0005] A method for eliminating stress-induced phase transformation during the preparation of diffusion couples in Ti-V-Mo alloys includes the following steps:

[0006] (1) The high-purity metallic titanium, vanadium and molybdenum raw materials are appropriately proportioned according to the phase diagram information to ensure that the alloy composition after melting is in the bcc single-phase region when it is solidified at high temperature.

[0007] (2) The proportioned raw materials are smelted in a vacuum non-consumable melting furnace to ensure that each sample is smelted at least 6 times.

[0008] (3) The smelted sample is homogenized and annealed in an argon atmosphere, and the annealed sample is then polished and mirror-polished.

[0009] (4) The diffusion couple was prepared by using spark plasma sintering technology.

[0010] (5) The prepared diffusion couple is vacuum sealed and subjected to solution heat treatment at a temperature higher than the β phase transition point, and then quenched.

[0011] In a preferred embodiment of the present invention, the molar content of Mo and V in the Ti-V-Mo system titanium alloy is 5%-20%.

[0012] In a preferred embodiment of the present invention, in step (2), the vacuum degree of vacuum melting is 4×10⁻⁶. -3 Pa~6×10 -3 Pa.

[0013] In a preferred embodiment of the present invention, in step (3), the homogenization annealing treatment is carried out at a temperature of 1100-1300℃ for 60-100h.

[0014] As a preferred embodiment of the present invention, in step (4), the discharge plasma sintering process parameters are pressure of 7-10 kN, temperature of 700-850 °C, and time of 6-12 min.

[0015] In a preferred embodiment of the present invention, the solution temperature in step (5) is 1100-1200℃ and the time is 20-50h.

[0016] Another objective of this invention is to provide the application of the Ti-V-Mo alloy diffusion couple prepared by the method in establishing a database of atomic mobility parameters for Ti-V-Mo alloys. Specifically, after polishing the Ti-V-Mo alloy diffusion couple, its compositional distance curve is analyzed using electron probe microanalysis. Then, the atomic mobility parameters database for Ti-V-Mo alloys can be established by calculating using Thermo-calc software.

[0017] The beneficial effects of this invention are:

[0018] (1) Using a vacuum non-consumable melting furnace for multiple meltings can ensure that the melted sample is in a stable single phase and can effectively avoid the enrichment of Mo elements and the appearance of β spots during the melting process. If the compound is present, it is difficult to eliminate it through subsequent heat treatment.

[0019] (2) The smelted sample is subjected to homogenization annealing. First, annealing at a high temperature for a long time followed by quenching can ensure that the sample is in the bcc single-phase region. Second, it can eliminate inclusions in the smelting process and avoid the occurrence of inclusions in the experiment, which would lead to inaccurate measurement data. Finally, it can transform the coarse dendrites of the smelting into uniform equiaxed crystals, and the grains can grow fully, greatly avoiding the influence of grain boundary diffusion.

[0020] (3) The temperature during spark plasma sintering may be lower than the phase transformation point of titanium alloy, and the diffusion couple undergoes a β→α transformation. By solution heat treatment and holding at a certain temperature for a certain period of time, the diffusion couple can be placed in the bcc single-phase region, and the diffusion couple can undergo a certain degree of diffusion along the interface.

[0021] Due to the high temperature and high pressure conditions of the spark plasma sintering process, the entire sintering cycle is relatively short. This makes the production efficiency of bulk metal diffusion couples high, especially when large-scale production is required. By adjusting the process parameters of spark plasma sintering, the microstructure and performance of bulk metal diffusion couples can be precisely controlled. Therefore, spark plasma sintering has a series of advantages such as high efficiency and controllability, which can avoid the occurrence of stress-induced phase transformation during diffusion couple preparation. Attached Figure Description

[0022] Figure 1 The SEM image of the diffusion couple interface prepared by spark plasma sintering technology in Example 1 of the present invention is shown.

[0023] Figure 2 The composition-distance curve at the diffusion couple interface was prepared using spark plasma sintering technology in Example 1 of this invention.

[0024] Figure 3 To compare with Example 1, a fixture was used to prepare SEM images of the diffusion couple interface.

[0025] Figure 4 The SEM image of the diffusion couple interface prepared by spark plasma sintering technology in Example 2 of the present invention is shown.

[0026] Figure 5 In Example 2 of this invention, the composition-distance curve at the diffusion couple interface was prepared using spark plasma sintering technology.

[0027] Figure 6 To compare with Example 2, a SEM image of the diffusion couple interface was prepared using a fixture. Detailed Implementation

[0028] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0029] Example 1

[0030] A method for eliminating stress-induced phase transformation during the preparation of titanium alloy diffusion couples includes the following steps:

[0031] (1) The diffusion couple sample prepared in this embodiment has the composition of Ti-15.9V and Ti-18.3Mo.

[0032] (2) The proportioned raw materials are smelted in a vacuum non-consumable melting furnace, wherein the vacuum degree is 5×10 -3 Pa, and ensure that each sample is melted at least 6 times.

[0033] (3) The molten sample was subjected to homogenization annealing at 1200℃ for 88 hours in an argon atmosphere and then water-cooled. The annealed sample was then polished and mirror-polished.

[0034] (4) The diffusion couple was prepared by spark plasma sintering technology with a pressure of 8.8 kN, a heat treatment temperature of 800 °C and a time of 8 min.

[0035] (5) The prepared diffusion couple is vacuum sealed and subjected to solution heat treatment at 1200℃ for 24 hours, and then quenched.

[0036] (6) After the quenched diffusion couple is polished, its composition distance curve is analyzed by electron probe microanalysis. Then, the diffusion kinetics database of Ti-V-Mo system titanium alloy can be established by calculation using Thermo-calc software.

[0037] At the interface of the titanium alloy diffusion couple prepared in this embodiment ( Figure 1 Observation revealed that the diffusion couple was well prepared; its composition-distance curve ( Figure 2Analysis shows that the diffusion couples are bonded together, with a significant concentration gradient at the interface, and diffusion occurs without stress-induced phase transformation, ensuring that both ends of the sample are in the bcc single-phase region. Therefore, this process can effectively guide the preparation of titanium alloy diffusion couples.

[0038] Example 2

[0039] A method for eliminating stress-induced phase transformation during the preparation of titanium alloy diffusion couples includes the following steps:

[0040] (1) The diffusion couple sample prepared in this embodiment consists of Ti and Ti-15V-5Mo.

[0041] (2) The proportioned raw materials are smelted in a vacuum non-consumable melting furnace, wherein the vacuum degree is 4×10 -3 Pa, and ensure that each sample is melted at least 6 times.

[0042] (3) The molten sample was subjected to homogenization annealing treatment at a temperature of 1100℃ for 100h in an argon atmosphere and then water-cooled. The annealed sample was then polished and mirror-polished.

[0043] (4) The diffusion couple was prepared by spark plasma sintering technology with a pressure of 10 kN, a heat treatment temperature of 700 °C and a time of 12 min.

[0044] (5) The prepared diffusion couple is vacuum sealed and subjected to solution heat treatment at 1100℃ for 50h, and then quenched.

[0045] (6) After the quenched diffusion couple is polished, its composition distance curve is analyzed by electron probe microanalysis. Then, the diffusion kinetics database of Ti-V-Mo system titanium alloy can be established by calculation using Thermo-calc software.

[0046] At the interface of the titanium alloy diffusion couple prepared in this embodiment ( Figure 4 Observation revealed that the diffusion couple was well prepared; its composition-distance curve ( Figure 5 Analysis shows that the diffusion couples are bonded together, with a significant concentration gradient at the interface, and diffusion occurs without stress-induced phase transformation, ensuring that both ends of the sample are in the bcc single-phase region. Therefore, this process can effectively guide the preparation of titanium alloy diffusion couples.

[0047] Example 3

[0048] A method for eliminating stress-induced phase transformation during the preparation of titanium alloy diffusion couples includes the following steps:

[0049] (1) The diffusion couple sample prepared in this embodiment consists of Ti and Ti-16V-8Mo.

[0050] (2) The proportioned raw materials are smelted in a vacuum non-consumable melting furnace, wherein the vacuum degree is 4×10 -3 Pa, and ensure that each sample is melted at least 6 times.

[0051] (3) The molten sample was subjected to homogenization annealing treatment at a temperature of 1300℃ for 60 hours in an argon atmosphere and then water-cooled. The annealed sample was then polished and mirror-polished.

[0052] (4) The diffusion couple was prepared by spark plasma sintering technology with a pressure of 7 kN, a heat treatment temperature of 850℃ and a time of 6 min.

[0053] (5) The prepared diffusion couple is vacuum sealed and subjected to solution heat treatment at 1200℃ for 20h, and then quenched.

[0054] (6) After the quenched diffusion couple is polished, its composition distance curve is analyzed by electron probe microanalysis. Then, the diffusion kinetics database of Ti-V-Mo system titanium alloy can be established by calculation using Thermo-calc software.

[0055] The diffusion couple prepared in this embodiment has a significant concentration gradient at the interface, and diffusion occurs without stress-induced phase transition, ensuring that both ends of the sample are in the bcc single-phase region.

[0056] Comparative Example 1

[0057] A method for eliminating stress-induced phase transformation during the preparation of titanium alloy diffusion couples includes the following steps:

[0058] (1) The diffusion couple sample prepared in this embodiment has the composition of Ti-15.1V and Ti-18.6Mo.

[0059] (2) The proportioned raw materials are smelted in a vacuum non-consumable melting furnace, wherein the vacuum degree is 5×10 -3 Pa and ensure that each sample is melted at least 6 times.

[0060] (3) The molten sample was subjected to homogenization annealing at 1200℃ for 88 hours in an argon atmosphere and then water-cooled. The annealed sample was then polished and mirror-polished.

[0061] (4) Use a clamp to press the diffusion couple to be prepared together and tighten the screws at both ends.

[0062] (5) Place the fixture with the diffusion couple in a vacuum annealing furnace at 900℃ and keep it at that temperature for 3 hours before air cooling.

[0063] (6) The prepared diffusion couple is vacuum sealed and subjected to solution heat treatment at 1200℃ for 24 hours, and then quenched.

[0064] (7) After the quenched diffusion couple is polished, its composition distance curve is analyzed by electron probe microanalysis.

[0065] In this comparative example, the interface of the diffusion couple was observed ( Figure 3 It is evident that there is a different contrast along the interface, and there are many fine and dispersed precipitates at the interface. The reason for this phenomenon may be that the stress-induced phase transformation caused by the high pressure during the preparation of the diffusion couple caused the originally single bcc phase to become a martensitic phase. Therefore, composition-distance curve analysis could not be performed, leading to the failure of the experiment.

[0066] Comparative Example 2

[0067] A method for eliminating stress-induced phase transformation during the preparation of titanium alloy diffusion couples includes the following steps:

[0068] (1) The diffusion couple sample prepared in this embodiment consists of Ti- and Ti-15V-5Mo.

[0069] (2) The proportioned raw materials are smelted in a vacuum non-consumable melting furnace, wherein the vacuum degree is 4.5×10 - 3 Pa and ensure that each sample is melted at least 6 times.

[0070] (3) The molten sample was subjected to homogenization annealing at 1200℃ for 88 hours in an argon atmosphere and then water-cooled. The annealed sample was then polished and mirror-polished.

[0071] (4) Use a clamp to press the diffusion couple to be prepared together and tighten the screws at both ends.

[0072] (5) Place the fixture with the diffusion couple in a vacuum annealing furnace at 900℃ and keep it at that temperature for 4 hours before air cooling.

[0073] (6) The prepared diffusion couple is vacuum sealed and subjected to solution heat treatment at 1100℃ for 48h, and then quenched.

[0074] (7) After the quenched diffusion couple is polished, its composition distance curve is analyzed by electron probe microanalysis.

[0075] In this comparative example, the interface of the diffusion couple was observed ( Figure 6It is evident that there are large gaps along the interface. The reason for this phenomenon is that the parameters could not be accurately controlled during the preparation of the diffusion couple in the fixture. As a result, when the pressure is low, the samples cannot be bonded together, and no diffusion occurs at the interface. Therefore, composition-distance curve analysis cannot be performed, leading to the failure of the experiment.

[0076] Comparative Example 3

[0077] A method for eliminating stress-induced phase transformation during the preparation of titanium alloy diffusion couples includes the following steps:

[0078] (1) The diffusion couple sample prepared in this embodiment has the composition of Ti-15.9V and Ti-18.3Mo.

[0079] (2) The proportioned raw materials are smelted in a vacuum non-consumable melting furnace, wherein the vacuum degree is 5×10 -3 Pa, and ensure that each sample is melted at least 6 times.

[0080] (3) The molten sample was subjected to homogenization annealing at 1200℃ for 88 hours in an argon atmosphere and then water-cooled. The annealed sample was then polished and mirror-polished.

[0081] (4) The diffusion couple was prepared by spark plasma sintering technology with a pressure of 6 kN, a heat treatment temperature of 650℃ and a time of 8 min.

[0082] (5) Observe the prepared diffusion couple under a scanning electron microscope.

[0083] In this comparative example, there is a large gap along the interface of the diffusion couple. The reason for this phenomenon is that when the diffusion couple is prepared by spark plasma sintering at a low temperature and low pressure, the samples cannot be bonded together and no diffusion occurs at the interface. Therefore, composition-distance curve analysis cannot be performed, leading to the failure of the experiment.

[0084] Comparative Example 4

[0085] A method for eliminating stress-induced phase transformation during the preparation of titanium alloy diffusion couples includes the following steps:

[0086] (1) The diffusion couple sample prepared in this embodiment has the composition of Ti-15.9V and Ti-18.3Mo.

[0087] (2) The proportioned raw materials are smelted in a vacuum non-consumable melting furnace, wherein the vacuum degree is 5×10 -3 Pa, and ensure that each sample is melted at least 6 times.

[0088] (3) The molten sample was subjected to homogenization annealing at 1200℃ for 88 hours in an argon atmosphere and then water-cooled. The annealed sample was then polished and mirror-polished.

[0089] (4) The diffusion couple was prepared by spark plasma sintering technology with a pressure of 12kN, a heat treatment temperature of 950℃ and a time of 8min.

[0090] (5) Observe the prepared diffusion couple under a scanning electron microscope.

[0091] In this comparative example, the diffusion couple exhibits varying contrast along the interface, and there are numerous finely dispersed precipitates at the interface. This phenomenon may be caused by stress-induced phase transformation due to the high pressure during spark plasma sintering to prepare the diffusion couple, which causes the originally singular bcc phase to develop into a martensitic phase. Therefore, composition-distance curve analysis cannot be performed, leading to the failure of the experiment.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for eliminating stress-induced phase transformation during the preparation of diffusion couples in Ti-V-Mo alloys, characterized in that, Includes the following steps: (1) The high-purity metallic titanium, vanadium and molybdenum raw materials are appropriately proportioned according to the phase diagram information to ensure that the alloy composition after melting is in the bcc single-phase region during high-temperature solid solution; (2) The proportioned raw materials are smelted in a vacuum non-consumable melting furnace to ensure that each sample is smelted at least 6 times; (3) The molten sample is subjected to homogenization annealing in an argon atmosphere, and the annealed sample is then polished and mirror-polished. (4) The diffusion couple was prepared by spark plasma sintering technology. The process parameters of spark plasma sintering were: pressure 7-10 kN, temperature 700-850℃, and time 6-12 min. (5) The prepared diffusion couple is vacuum sealed and subjected to solution heat treatment at a temperature higher than the β phase transformation point, followed by water cooling, to obtain a Ti-V-Mo alloy diffusion couple containing only the bcc single phase and without stress-induced phase transformation. The molar content of Mo and V in the Ti-V-Mo system titanium alloy is 5%-20%; In step (3), the homogenization annealing treatment is carried out at a temperature of 1100-1300℃ for 60-100h. In step (5), the solution temperature is 1100-1200℃ and the time is 20-50h.

2. The method for eliminating stress-induced phase transformation during the preparation of diffusion couples in Ti-V-Mo alloys according to claim 1, characterized in that, In step (2), the vacuum degree of vacuum melting is 4×10⁻⁶. -3 Pa~6×10 -3 Pa.

3. The application of the Ti-V-Mo alloy diffusion couple prepared by the method of any one of claims 1 to 2 in establishing a database of atomic mobility parameters of Ti-V-Mo alloys is as follows: after polishing the Ti-V-Mo alloy diffusion couple, its compositional distance curve is analyzed by electron probe microanalysis, and then the atomic mobility parameter database of Ti-V-Mo alloys can be established by calculation using Thermo-calc software.

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