A method for preparing a stress-inducible phase transformation-free Ti-Mo-Cr alloy diffusion couple

Abstract

This invention discloses a method for preparing a Ti-Mo-Cr alloy diffusion couple without stress-induced phase transformation, belonging to the field of titanium alloy diffusion technology. This invention utilizes hot isostatic pressing (HIP) 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 enabling effective subsequent experimental research and avoiding blindly setting experimental parameters. On the other hand, it allows for precise control, greatly avoiding the occurrence of stress-induced phase transformation or gaps at the diffusion couple interface due to inaccurate parameter control during fixture preparation, which could lead to experimental failure. This invention enables the preparation of diffusion couples that conform to diffusion concentration gradient experiments, which can 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 preparing a Ti-Mo-Cr alloy diffusion couple without stress-induced phase transformation. Background Technology

[0002] Ti-Mo-Cr alloys are widely used in aerospace, marine engineering, and medical devices due to their superior strength and lightweight properties, excellent corrosion resistance, good biocompatibility, and high-temperature stability. However, the processing and subsequent heat treatment often involve a "cooking-style" approach, requiring significant time, money, and effort. Establishing an atomic mobility parameter database using the CALPHAD (CALculation of PHAse Diagram) method can provide comprehensive and accurate information for materials science research. This database not only helps predict the thermodynamic and kinetic properties of materials but also supports phase transition studies, thermodynamic modeling, and the design of novel materials. By gaining a deeper understanding of atomic mobility in crystals, it can optimize material processing, improve product performance, and explore the structure and properties of materials through simulation and computational methods. In the database development process, preparing diffusion couples and determining their composition-distance curves are indispensable experimental steps.

[0003] With the rapid development of engine components, the requirements for titanium alloys have evolved from the side-shaping of the previous two generations to the current focus on improving the comprehensive mechanical properties of the alloys and developing advanced forming processes. To further improve the room temperature performance, high-temperature hot working performance, and oxidation resistance of the alloys, Mo and Cr are often added as β-stabilizing elements, also known as β-solidified alloys, whose initial solidification structure is the β phase. β-solidified alloys have a fine and uniform as-cast structure and excellent hot working performance. Because they can effectively eliminate compositional and microstructural inhomogeneities and reduce casting texture, thereby improving the ductility and high-temperature strength of the alloys, this has become a current research hotspot in the field of titanium alloys.

[0004] Because Ti-Mo-Cr alloys have high service temperatures and their microstructure is in the β single-phase state (i.e., possessing a bcc single-phase structure), diffusion couple technology can be used to determine the composition-distance curve of this system, solve for the diffusion coefficient, and establish an atomic mobility parameter database to better guide alloy design and subsequent heat treatment processes. During the preparation of diffusion couples, the material is in an unstable state. When the applied force is small, the alloy samples cannot bond together, resulting in gaps at the interface and no diffusion. When the applied force is large, stress-induced martensitic transformation easily occurs, causing a phase transformation at the diffusion couple interface. This results in the material not being in the bcc single-phase region, making it impossible to accurately characterize its diffusion behavior in the β single-phase region and establish 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

[0005] The purpose of this invention is to provide a method for preparing a Ti-Mo-Cr alloy diffusion couple without stress-induced phase transformation, which can produce a diffusion couple with single phases at both ends, good adhesion, and no stress-induced phase transformation phenomenon, including the following steps:

[0006] (1) The raw materials of titanium, chromium and molybdenum with a purity of 99.99% are proportioned according to the isothermal section of the phase diagram of the system to ensure that the alloy composition after melting is in the bcc single phase region when it is dissolved 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 hot isostatic pressing. The pressure during the preparation process was 120-200 MPa, the temperature was 850-1000℃, and the time was 3-6 h.

[0010] (5) The prepared diffusion couple is vacuum sealed and subjected to solution heat treatment at a temperature higher than the β phase transformation point, and then quenched to obtain a Ti-Mo-Cr alloy diffusion couple without stress-induced phase transformation.

[0011] Preferably, the molar content of Mo and Cr in the Ti-Mo-Cr alloy of the present invention is 3%-20%.

[0012] Preferably, the vacuum degree of the vacuum melting process in this invention is 4 × 10⁻⁶. -3 Pa~6×10 -3 Pa.

[0013] Preferably, in step (3) of the present invention, the homogenization annealing treatment temperature is 1200-1300℃ and the time is 60-100h.

[0014] Preferably, in step (5) of the present invention, the solution temperature is 1100-1200℃ and the time is 20-50h.

[0015] Another objective of this invention is to provide the application of the Ti-Mo-Cr alloy diffusion couple prepared by the method in establishing a database of atomic mobility parameters for Ti-Mo-Cr alloys. Specifically, after polishing the Ti-Mo-Cr alloy diffusion couple, its compositional distance curve is analyzed using electron probe microanalysis. Then, the atomic mobility parameters database for Ti-Mo-Cr alloys can be established by calculating using Thermo-calc software.

[0016] Establishing a database of atomic mobility parameters not only allows for more accurate prediction of material properties, particularly those related to diffusion, migration, and deformation, but also accelerates the development of new materials. Researchers can screen and select from large datasets to identify potential candidate materials with specific properties, thereby reducing the time and cost of experimental trial and error. For titanium alloys, heat treatment is typically performed in the β single-phase region, thus requiring the establishment of a database of atomic mobility parameters in the bcc single-phase region. Preparing diffusion couple samples that meet experimental requirements is fundamental to establishing this database. This invention allows for the preparation of diffusion couples that meet experimental requirements by adjusting process parameters, thereby enabling effective subsequent experimental research and avoiding the blind setting of experimental parameters. Furthermore, it allows for precise control, greatly reducing the risk of experimental failure due to stress-induced phase transformation or interfacial gaps caused by inaccurate parameter control during fixture preparation. This invention enables the preparation of diffusion couples that meet the requirements of electron probe microanalysis, facilitating the subsequent establishment of a database of atomic mobility parameters for titanium alloys.

[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 Cr element segregation and the occurrence of segregation compound Cr2Ti during the melting process. If this compound exists, it is difficult to eliminate it through subsequent heat treatment, which affects the performance of the diffusion couple.

[0019] (2) The annealing of the smelted sample is homogenized. 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 the inclusions in the smelting process and avoid the inaccuracy of the measurement data caused by the appearance of inclusions in the experiment. 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) During hot isostatic pressing, the temperature may be lower than the phase transformation point of the 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. Attached Figure Description

[0021] Figure 1 The SEM image of the diffusion couple interface was prepared using hot isostatic pressing in Embodiment 1 of the present invention.

[0022] Figure 2 In Example 1 of this invention, the composition-distance curve at the diffusion couple interface was prepared using hot isostatic pressing.

[0023] Figure 3To compare with Example 1, a fixture was used to prepare SEM images of the diffusion couple interface.

[0024] Figure 4 The SEM image of the diffusion couple interface was prepared using hot isostatic pressing in Embodiment 2 of the present invention.

[0025] Figure 5 In Example 2 of this invention, the composition-distance curve at the diffusion couple interface was prepared using hot isostatic pressing.

[0026] Figure 6 To compare with Example 2, a SEM image of the diffusion couple interface was prepared using a fixture. Detailed Implementation

[0027] 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.

[0028] Example 1

[0029] A method for stress-free induced phase transformation during the preparation of titanium alloy diffusion couples includes the following steps:

[0030] (1) The diffusion couple sample prepared in this embodiment consists of Ti-15Cr and Ti-10.6Mo.

[0031] (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.

[0032] (3) The molten sample was subjected to homogenization annealing treatment at a temperature of 1200℃ for 90 hours in an argon atmosphere and then water-cooled. The annealed sample was then polished and mirror-polished.

[0033] (4) The diffusion couple was prepared by hot isostatic pressing (HIP) at a pressure of 150 MPa, a temperature of 950 °C, and a time of 5 h.

[0034] (5) The prepared diffusion couple is vacuum sealed and subjected to solution heat treatment at 1200℃ for 26 hours, and then quenched.

[0035] (6) After the quenched diffusion couple is polished, its compositional distance curve is analyzed by electron probe microanalysis. Then, the atomic mobility parameter database of Ti-Mo-Cr alloy can be established by calculating with Thermo-calc software.

[0036] At the interface of the 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.

[0037] Example 2

[0038] A method for stress-free induced phase transformation during the preparation of titanium alloy diffusion couples includes the following steps:

[0039] (1) The diffusion couple sample prepared in this embodiment has the composition of Ti and Ti-17.3Cr-4.6Mo.

[0040] (2) The proportioned raw materials are smelted in a vacuum non-consumable melting furnace, wherein the vacuum degree is 6×10 -3 Pa, and ensure that each sample is melted at least 6 times.

[0041] (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.

[0042] (4) The diffusion couple was prepared by hot isostatic pressing (HIP) at a pressure of 180 MPa, a temperature of 1000 °C, and a time of 4 h.

[0043] (5) The prepared diffusion couple is vacuum sealed and subjected to solution heat treatment at 1100℃ for 50h, and then quenched.

[0044] (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-Mo-V alloy can be established by calculating with Thermo-calc software.

[0045] At the interface of the 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.

[0046] Example 3

[0047] A method for stress-free induced phase transformation during the preparation of titanium alloy diffusion couples includes the following steps:

[0048] (1) The diffusion couple sample prepared in this embodiment consists of Ti and Ti-20Cr-10Mo.

[0049] (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.

[0050] (3) The molten sample was subjected to homogenization annealing at 1250℃ for 100h in an argon atmosphere and then water-cooled. The annealed sample was then polished and mirror-polished.

[0051] (4) The diffusion couple was prepared by hot isostatic pressing (HIP) at a pressure of 200 MPa, a temperature of 850 °C, and a time of 6 h.

[0052] (5) The prepared diffusion couple is vacuum sealed and subjected to solution heat treatment at 1200℃ for 20h, and then quenched.

[0053] (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-Mo-V alloy can be established by calculating with Thermo-calc software.

[0054] 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.

[0055] Comparative Example 1

[0056] A method for stress-free induced phase transformation during the preparation of titanium alloy diffusion couples includes the following steps:

[0057] (1) The diffusion couple sample prepared in this embodiment consists of Ti-15Cr and Ti-10.6Mo.

[0058] (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.

[0059] (3) The molten sample was subjected to homogenization annealing treatment at a temperature of 1200℃ for 90 hours in an argon atmosphere and then water-cooled. The annealed sample was then polished and mirror-polished.

[0060] (4) Use a clamp to press the diffusion couple to be prepared together and tighten the screws at both ends.

[0061] (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.

[0062] (6) The prepared diffusion couple is vacuum sealed and subjected to solution heat treatment at 1200℃ for 26 hours, and then quenched.

[0063] (7) After the quenched diffusion couple is polished, its composition distance curve is analyzed by electron probe microanalysis.

[0064] 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.

[0065] Comparative Example 2

[0066] A method for stress-free induced phase transformation during the preparation of titanium alloy diffusion couples includes the following steps:

[0067] (1) The diffusion couple sample prepared in this embodiment has the composition of Ti and Ti-17.3Cr-4.6Mo.

[0068] (2) The proportioned raw materials are smelted in a vacuum non-consumable melting furnace, wherein the vacuum degree is 6×10 -3 Pa, and ensure that each sample is melted at least 6 times.

[0069] (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.

[0070] (4) Use a clamp to press the diffusion couple to be prepared together and tighten the screws at both ends.

[0071] (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.

[0072] (6) The prepared diffusion couple is vacuum sealed and subjected to solution heat treatment at 1100℃ for 50h, and then quenched.

[0073] (7) After the quenched diffusion couple is polished, its composition distance curve is analyzed by electron probe microanalysis.

[0074] 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.

[0075] Comparative Example 3

[0076] A method for stress-free induced phase transformation during the preparation of titanium alloy diffusion couples includes the following steps:

[0077] (1) The diffusion couple sample prepared in this embodiment consists of Ti-15Cr and Ti-10.6Mo.

[0078] (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.

[0079] (3) The molten sample was subjected to homogenization annealing treatment at a temperature of 1200℃ for 90 hours in an argon atmosphere and then water-cooled. The annealed sample was then polished and mirror-polished.

[0080] (4) The diffusion couple was prepared by hot isostatic pressing (HIP) at a pressure of 100 MPa, a temperature of 750 °C, and a time of 5 h.

[0081] (5) Observe the prepared diffusion couple under a scanning electron microscope.

[0082] In this comparative example, there is a large gap at the interface of the diffusion couple. The reason for this phenomenon is that when the temperature and pressure are low during the preparation of the diffusion couple using hot isostatic pressing, 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.

[0083] Comparative Example 4

[0084] A method for stress-free induced phase transformation during the preparation of titanium alloy diffusion couples includes the following steps:

[0085] (1) The diffusion couple sample prepared in this embodiment consists of Ti-15Cr and Ti-10.6Mo.

[0086] (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.

[0087] (3) The molten sample was subjected to homogenization annealing treatment at a temperature of 1200℃ for 90 hours in an argon atmosphere and then water-cooled. The annealed sample was then polished and mirror-polished.

[0088] (4) The diffusion couple was prepared by hot isostatic pressing (HIP) at a pressure of 240 MPa, a temperature of 1050 °C, and a time of 5 h.

[0089] (5) Observe the prepared diffusion couple under a scanning electron microscope.

[0090] In this comparative example, the diffusion couples exhibit different contrasts at their interfaces, and there are numerous finely dispersed precipitates at the interfaces. This phenomenon may be due to the high pressure exerted during the hot isostatic pressing (HIP) preparation of the diffusion couples, resulting in a stress-induced phase transformation that causes the originally singular bcc phase to develop into a martensitic phase. Consequently, composition-distance curve analysis cannot be performed, leading to the failure of the experiment.

[0091] 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 preparing a stress-free Ti-Mo-Cr alloy diffusion couple, characterized in that, Includes the following steps: (1) The raw materials of titanium, chromium and molybdenum with a purity of 99.99% are proportioned according to the isothermal section of the phase diagram of the system 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 hot isostatic pressing. The pressure during the preparation process was 120-200 MPa, the temperature was 850-1000℃, and the time was 3-6 h. (5) The prepared diffusion couple is vacuum sealed and subjected to solution heat treatment at a temperature higher than the β phase transformation point, and then quenched to obtain a Ti-Mo-Cr alloy diffusion couple with bcc single phase and no stress-induced phase transformation. The molar content of Mo and Cr in the Ti-Mo-Cr alloy is 3%-20%; In step (3), the homogenization annealing treatment is carried out at a temperature of 1200-1300℃ for 60-100h. In step (5), the solution temperature is 1100-1200℃ and the time is 20-50h.

2. The method for preparing the stress-free Ti-Mo-Cr alloy diffusion couple according to claim 1, characterized in that: The vacuum degree of vacuum melting is 4×10 -3 Pa~6×10 -3 Pa.

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

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