A Co-Hf-Ta ternary diffusion couple and its preparation method

Abstract

This invention belongs to the field of diffusion couple preparation and phase diagram determination technology, specifically relating to a Co-Hf-Ta ternary diffusion couple and its preparation method. The method uses pure metal blocks of Co, Hf, and Ta with a purity of 99.95% as raw materials. After wire cutting via electrical discharge machining, the pressing interface is mechanically ground and polished. Subsequently, binary pressing is performed using a graphite mold and spark plasma sintering (SPS) process. Then, ternary pressing is performed using the binary pressed block as an intermediate layer to obtain a Co-Hf-Ta ternary metal block. Afterward, the ternary metal block is coated with a Ta sheet and placed in a quartz tube, subjected to diffusion annealing at 1173 K for 30 days, and then water quenched to obtain the Co-Hf-Ta ternary diffusion couple. The diffusion couple sample is characterized after metallographic hot mounting, grinding, and polishing. The results show that the Co-Hf-Ta ternary diffusion couple prepared by this invention has a tight interface, a continuous diffusion layer, and a stable structure. It can simultaneously obtain diffusion and phase equilibrium information of Co-Hf, Co-Ta, and Hf-Ta systems, and is suitable for phase diagram construction and diffusion behavior research of Co-Hf-Ta systems.

Description

Technical Field

[0001] This invention relates to the field of diffusion couple preparation and phase diagram determination technology, and in particular to a Co-Hf-Ta ternary diffusion couple prepared by a graphite mold and a spark plasma sintering (SPS) pressing process, and the preparation method thereof. Background Technology

[0002] The diffusion couple method is an experimental technique that utilizes the interdiffusion between different metals or alloys to form a continuous compositional gradient and diffusion layer structure in a single sample. By analyzing the microstructure, phase composition, and elemental distribution of the diffusion region, the phase equilibrium relationship, diffusion path, and interfacial migration behavior in multi-component systems can be obtained simultaneously. Therefore, it is widely used in the determination of phase diagrams for binary and multi-component alloys, diffusion kinetics research, and high-temperature material design.

[0003] Currently, multi-component diffusion couples are typically fabricated using simple mechanical bonding, spot welding, or brazing. Simple mechanical bonding relies mainly on manual clamping or ordinary fixtures, resulting in uneven interfacial pressure and limited contact area. During prolonged high-temperature annealing, this can easily lead to interfacial gaps, localized debonding, and discontinuous diffusion layers. While spot welding and brazing can improve connection stability, they usually require the introduction of solder or intermediate layer elements, which can easily form additional intermediate phases or contaminant layers at the diffusion interface, thus affecting the intrinsic diffusion and phase equilibrium behavior of the target system.

[0004] Furthermore, for the Co-Hf-Ta ternary system, publicly available experimental phase diagrams and diffusion data are still limited, and a dedicated diffusion couple preparation process suitable for large-area tight bonding, stable multi-interface connection, and long-term high-temperature diffusion annealing is lacking. Especially when multiple metals are combined to form a ternary diffusion joint, the refractory metals such as Hf and Ta have limited plastic deformation capabilities and differ in their coefficients of thermal expansion from Co, which can easily lead to insufficient interfacial adhesion during multi-metal combination. Traditional methods are insufficient to guarantee interfacial smoothness and structural stability during long-term heat treatment.

[0005] Therefore, it is necessary to provide a method for preparing Co-Hf-Ta ternary diffusion couples by combining graphite molds with SPS pressing technology, so as to achieve large-area close contact between multi-metal blocks, improve the interface quality of diffusion couples and experimental repeatability. Summary of the Invention

[0006] The purpose of this invention is to provide a Co-Hf-Ta ternary diffusion couple and its preparation method. By using a graphite mold and a spark plasma sintering (SPS) pressing process, a large-area stable contact between multiple metal blocks is achieved, resulting in a Co-Hf-Ta ternary diffusion couple with a smooth interface, continuous diffusion layer, and good repeatability.

[0007] This invention is achieved through the following technical solution:

[0008] S1. Raw material preparation and wire cutting: Select pure metal blocks of Co, Hf and Ta with a purity of not less than 99.95%, and use electric spark wire cutting to cut the Hf and Ta metal blocks into metal blocks of 5 mm × 5 mm × 5 mm respectively, and cut the Co metal block into metal blocks of 5 mm × 5 mm × 15 mm.

[0009] S2. Preparation of Ta / Hf / Ta binary pressed block: The interface to be pressed is mechanically ground and polished. Two Ta metal blocks and one Hf metal block are arranged sequentially along the length direction and placed in a graphite mold. The axial pressure is applied through the graphite cover in the discharge plasma sintering (SPS) equipment to press the Ta / Hf / Ta binary pressed block.

[0010] S3. Preparation of Co-Hf-Ta ternary pressed block: The interface to be pressed is mechanically ground and polished. The Ta / Hf / Ta binary pressed block obtained in step S2 is placed in the middle position, and Co metal blocks are placed on both sides of it, so that the Co metal blocks are in contact with the sides of the Ta / Hf / Ta binary pressed block. Then it is placed in a graphite mold and pressed by applying axial pressure through the graphite cover in the spark plasma sintering (SPS) equipment to form the Co-Hf-Ta ternary pressed block.

[0011] S4. Diffusion annealing treatment: After coating the Ta sheet with the Co-Hf-Ta ternary press block obtained in step S3, the block is placed in a quartz tube and evacuated to a vacuum level not exceeding 10°C. -2 After Pa, argon gas was introduced and the tube was sealed. Diffusion annealing was carried out at 1173 K for 30 days, and then the tube was immediately taken out and water quenched to obtain a Co-Hf-Ta ternary diffusion couple with a continuous diffusion layer.

[0012] S5. Tissue and composition analysis: The diffusion couple sample was placed in the metallographic hot mounting machine mold, thermosetting mounting powder was added, and it was heated and pressed at 130 ℃ to obtain the metallographic mounting sample; then it was ground and polished in sequence, and the morphology of the diffusion layer was observed by scanning electron microscopy (SEM), and the composition was analyzed by electron probe microanalysis (EPMA).

[0013] Furthermore, all the graphite molds are cylindrical structures with a height of 30 mm and a diameter of 22 mm.

[0014] Furthermore, the graphite mold has a rectangular groove at the top that is 6 mm long, 6 mm wide, and 13 mm deep, for placing a binary pressed metal block. The depth of the groove is less than the height of the binary pressed metal block, so that the top part of the pressed metal block is exposed outside the groove.

[0015] Furthermore, the graphite mold has a rectangular groove at the top that is 15 mm long, 6 mm wide, and 13 mm deep, for placing a ternary pressed metal block. The depth of the groove is less than the height of the ternary pressed metal block, so that the top part of the pressed metal block is exposed outside the groove.

[0016] Furthermore, the pressing process in steps S2 and S3 is carried out in conjunction with the pressing of a cylindrical graphite cap, which is 10 mm high and 22 mm in diameter and is placed on top of the graphite mold. Axial pressure is applied by the SPS device to uniformly transmit the pressure to the metal block to be pressed, thereby improving the interface adhesion and structural stability.

[0017] Furthermore, the SPS pressing process in steps S2 and S3 is as follows: first, the temperature is raised from room temperature to 923 K at a heating rate of 100 K / min, then raised to 1023 K at a heating rate of 50 K / min, an axial pressure of 30 MPa is applied at 1023 K and held for 10 min, and then cooled to room temperature in the furnace.

[0018] Furthermore, in steps S2 and S3, the mechanical grinding and polishing processes are carried out by mechanical grinding with sandpaper of different grit sizes and polishing with metallographic polishing paste to make the surface of the pressed interface smooth and flat.

[0019] Furthermore, the diffusion annealing time in step S4 is 20 to 40 days, preferably 30 days.

[0020] Furthermore, before tissue observation in step S5, the diffusion couple sample needs to undergo metallographic mounting treatment. The mounting uses thermosetting resin mounting powder to form a standard metallographic mounting sample under heating and pressure conditions, so as to improve the stability of subsequent polishing and protect the integrity of the diffusion interface.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention uses a combination of graphite mold and SPS axial pressure to achieve large-area stable contact between multiple metal blocks, thereby improving the flatness and continuity of the diffusion couple interface.

[0023] (2) The present invention adopts a step-by-step construction method of "binary pressing + ternary pressing", which effectively avoids the problems of interface misalignment and local debonding when multiple metals are directly combined;

[0024] (3) The entire pressing process of this invention does not introduce solder or intermediate layer elements, which can avoid contamination by foreign elements and ensure the intrinsic diffusion and phase transition behavior of the Co-Hf-Ta system;

[0025] (4) The graphite mold used in this invention has good high temperature resistance and dimensional stability, which can ensure structural stability during long-term high-temperature diffusion annealing.

[0026] (5) The present invention uses a cylindrical graphite cap to assist SPS axial pressing, which can effectively improve the uniformity of pressure transmission, reduce the metal block displacement and local interface separation during the pressing process, thereby improving the interface bonding quality and experimental repeatability of the diffusion couple.

[0027] (6) The diffusion couple prepared by the present invention has a smooth interface and a continuous diffusion layer, which can meet the requirements of SEM tissue observation and EPMA elemental analysis, and provide reliable experimental samples for the construction of phase diagrams and diffusion behavior studies of the Co-Hf-Ta system. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments will be briefly introduced below.

[0029] Figure 1 A schematic diagram of the process for preparing Co-Hf-Ta ternary diffusion couples.

[0030] Figure 2 This is a schematic diagram of the binary and ternary pressing steps of the Co-Hf-Ta ternary diffusion couple of the present invention.

[0031] Figure 3 This is a photograph of the Co-Hf-Ta ternary diffusion couple sample after heat treatment in Example 1.

[0032] Figure 4 This is a SEM microstructure of the Co-Hf-Ta ternary diffusion couple after heat treatment in Example 1. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments. It should be noted that the embodiments described in this invention are merely preferred embodiments and are not intended to limit the invention. Various modifications and variations can be made to this invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Example 1

[0034] Pure metal blocks of Co, Hf, and Ta with a purity of 99.95% were selected.

[0035] The Hf and Ta metal blocks were cut into Hf metal blocks and Ta metal blocks with dimensions of 5 mm × 5 mm × 5 mm respectively by wire electrical discharge machining, and the Co metal block was cut into Co metal blocks with dimensions of 5 mm × 5 mm × 15 mm.

[0036] The bonding interface was mechanically ground with sandpaper of different grit sizes, and then polished with metallographic polishing paste until there were no obvious scratches on the surface.

[0037] A 5 mm × 5 mm × 5 mm Ta metal block, a 5 mm × 5 mm × 5 mm Hf metal block, and another 5 mm × 5 mm × 5 mm Ta metal block are arranged sequentially along their length and placed within a rectangular groove at the top of a binary graphite mold. The graphite mold is a cylindrical structure with a height of 30 mm and a diameter of 22 mm. The top has a rectangular groove measuring 6 mm in length, 6 mm in width, and 13 mm in depth. The height of the Ta / Hf / Ta binary pressing block is greater than the depth of the graphite mold groove, allowing its top portion to protrude outside the groove. This enables the graphite cap to directly contact the metal blocks and apply axial pressure during the SPS pressing process.

[0038] A cylindrical graphite cap, 10 mm high and 22 mm in diameter, is then placed on top of the graphite mold. The assembled graphite mold is placed in an SPS (Special Purpose Particulate Graphite) apparatus and heated from room temperature to 923 K at a rate of 100 K / min, then to 1023 K at a rate of 50 K / min. An axial pressure of 30 MPa is applied at 1023 K and held for 10 min. The pressure is then uniformly transferred to the Ta / Hf / Ta metal composite interface through a graphite punch and the graphite cap. The mold is then cooled to room temperature in the furnace to obtain a Ta / Hf / Ta binary composite block with dimensions of 5 mm × 5 mm × 15 mm.

[0039] Two 5 mm × 5 mm × 15 mm Co metal blocks are placed on either side of the Ta / Hf / Ta binary composite block, so that their sides are in contact to form a Co / Ta / Hf / Ta / Co composite structure, which is then placed in the rectangular groove at the top of the ternary graphite mold. The ternary graphite mold is a cylindrical structure with a height of 30 mm and a diameter of 22 mm. The top has a rectangular groove with a length of 15 mm, a width of 6 mm, and a depth of 13 mm. The height of the Co-Hf-Ta ternary composite structure is greater than the depth of the groove in the ternary graphite mold, so that the top part of the composite structure is exposed outside the groove, so that axial pressure can be applied to the graphite cap and the interface can be pressed together.

[0040] Subsequently, a cylindrical graphite cap with a height of 10 mm and a diameter of 22 mm is placed on top of the ternary graphite mold. The assembled ternary graphite mold is placed in an SPS device, and first heated from room temperature to 923 K at a heating rate of 100 K / min, then heated to 1023 K at a heating rate of 50 K / min. An axial pressure of 30 MPa is applied at 1023 K and held for 10 min. Axial pressure is applied through the graphite cap by a graphite punch, so that a large-area close contact is formed between the Co metal block and the Ta / Hf / Ta binary pressed block. Then, the mold is cooled to room temperature in the furnace to obtain the Co-Hf-Ta ternary pressed block.

[0041] The resulting ternary press block was coated with a Ta sheet and then placed into a quartz tube. A vacuum system was then connected, and the pressure was evacuated to no higher than 10. -2 After Pa, argon gas is introduced and the tube is sealed.

[0042] The encapsulated quartz tube was placed in a tube furnace and subjected to diffusion annealing at 1173 K for 30 days to allow Co, Hf and Ta to fully interdiffuse at each interface to form a continuous diffusion layer. After annealing, the tube was immediately quenched in water to obtain a Co-Hf-Ta ternary diffusion couple sample.

[0043] The diffusion couple sample was placed in the metallographic hot mounting machine mold, thermosetting mounting powder was added, and it was heated and pressed at 130 ℃ to obtain a cylindrical metallographic mounting sample. Subsequently, it was polished with sandpaper of different grits and polished with metallographic polishing paste until there were no obvious scratches on the sample surface.

[0044] The diffused couple cross section was then observed using backscattered electron imaging with scanning electron microscopy (SEM).

[0045] SEM results showed that multiple diffusion layer regions with different compositional characteristics could be observed along the diffusion direction. The interfaces of each diffusion layer were straight and continuous, without obvious macroscopic cracks or large-area pores. Compositional analysis combining SEM and EPMA confirmed that the diffusion layers contained CoHf2, CoHf, Co2Hf, Co3Hf, and Co... 23 Intermetallic compound phases such as Hf6, CoTa, CoTa2, and Co2Ta.

[0046] Further electron probe microanalysis (EPMA) was used to perform elemental line scanning and surface distribution analysis on the diffusion couple cross section. The results show that Co, Hf, and Ta elements exhibit continuous gradient changes along the diffusion direction, and regular composition-distance curves can be obtained, providing a reliable data foundation for subsequent phase diagram construction and diffusion coefficient calculation of the Co-Hf-Ta system.

[0047] Compared with diffusion couples prepared by traditional mechanical bonding, the present invention uses a graphite mold and SPS step-by-step pressing process, which significantly improves the degree of interface bonding and interface flatness; after long-term diffusion annealing at 1173 K, the diffusion layer is continuous and the interface is stable, and the experimental repeatability is significantly improved.

[0048] Compared to diffusion couples prepared using only simple mechanical contact or spot welding, this invention combines Ta / Hf / Ta binary bonding with Co / binary / Co ternary bonding, along with fine interface polishing, significantly improving interface bonding quality and structural stability. Traditional mechanical bonding-prepared Co-Hf-Ta diffusion couples are prone to discontinuities in the diffusion layer and localized debonding near the interface after prolonged annealing at 1173 K. In contrast, the diffusion couples prepared by this invention exhibit intact interfaces, stable diffusion layer morphology, and better repeatability.

[0049] Further EPMA surface scanning and local composition analysis results show that the Co-Hf-Ta ternary diffusion couple prepared in this invention can simultaneously obtain the composition and phase structure information of three binary systems (Co-Hf, Co-Ta, and Hf-Ta) and the Co-Hf-Ta ternary diffusion joint in the same sample under heat treatment conditions.

[0050] In summary, this invention achieves stable preparation of Co-Hf-Ta ternary diffusion couples by rationally designing the metal block size, graphite mold structure, and SPS stepwise pressing process. The prepared diffusion couples have tight interfacial bonding, continuous diffusion layers, and stable microstructure, which can meet the requirements of SEM microstructure observation and EPMA elemental analysis, providing a reliable experimental method for the construction of phase diagrams and the study of diffusion behavior of the Co-Hf-Ta system.

Claims

1. A method for preparing a Co-Hf-Ta ternary diffusion couple, characterized in that, Includes the following steps: S1. Raw material preparation and wire cutting: Select pure metal blocks of Co, Hf and Ta with a purity of 99.95%. Use electric spark wire cutting to cut the Hf and Ta metal blocks into metal blocks of 5 mm × 5 mm × 5 mm respectively, and cut the Co metal block into metal blocks of 5 mm × 5 mm × 15 mm. S2. Preparation of Ta / Hf / Ta binary pressed block: The interface to be pressed is mechanically ground and polished. Two Ta metal blocks and one Hf metal block are arranged sequentially along the length direction and placed in a graphite mold. The axial pressure is applied through the graphite cover in the discharge plasma sintering (SPS) equipment to press the Ta / Hf / Ta binary pressed block. S3. Preparation of Co-Hf-Ta ternary pressed block: The interface to be pressed is mechanically ground and polished. The Ta / Hf / Ta binary pressed block obtained in step S2 is placed in the middle position, and Co metal blocks are placed on both sides of it, so that the Co metal blocks are in contact with the sides of the Ta / Hf / Ta binary pressed block. Then it is placed in a graphite mold and pressed by applying axial pressure through the graphite cover in the spark plasma sintering (SPS) equipment to form the Co-Hf-Ta ternary pressed block. S4. Diffusion annealing treatment: After coating the Ta sheet with the Co-Hf-Ta ternary press block obtained in step S3, the block is placed in a quartz tube and evacuated to a vacuum level not exceeding 10°C. -2 After Pa, argon gas was introduced and the tube was sealed. Diffusion annealing was carried out at 1173 K for 30 days, followed by immediate water quenching to obtain a Co-Hf-Ta ternary diffusion couple with a continuous diffusion layer. S5. Tissue and composition analysis: After cutting the diffusion couple sample, it was placed in a metallographic mounting mold, thermosetting mounting powder was added, and it was hot-pressed and mounted at 130 ℃ to obtain a metallographic mounting sample that was easy to prepare for subsequent sample preparation. Then, the mounting sample was ground and polished in sequence, and the morphology of the diffusion layer was observed by scanning electron microscopy (SEM), and the composition was analyzed by electron probe microanalysis (EPMA).

2. The method for preparing the Co-Hf-Ta ternary diffusion couple according to claim 1, characterized in that, The graphite mold in step S2 is a cylindrical structure with a height of 30 mm and a diameter of 22 mm. The top has a rectangular groove with a length of 6 mm, a width of 6 mm, and a depth of 13 mm for placing the Ta / Hf / Ta binary metal block to be pressed. The depth of the groove is less than the height of the Ta / Hf / Ta binary metal block to be pressed, so that the top part of the binary metal block is exposed outside the groove. During the pressing process, the graphite cover directly applies axial pressure to the metal block to be pressed.

3. The method for preparing the Co-Hf-Ta ternary diffusion couple according to claim 1, characterized in that, The graphite mold in step S3 is a cylindrical structure with a height of 30 mm and a diameter of 22 mm. The top has a rectangular groove with a length of 15 mm, a width of 6 mm, and a depth of 13 mm for placing the Co / Ta / Hf / Ta / Co ternary metal block to be pressed. The depth of the groove is less than the height of the Co / Ta / Hf / Ta / Co ternary metal block to be pressed, so that the top part of the ternary metal block is exposed outside the groove. During the pressing process, the graphite cap directly applies axial pressure to the metal block to be pressed.

4. The method for preparing the Co-Hf-Ta ternary diffusion couple according to any one of claims 1 to 3, characterized in that, In both steps S2 and S3, the pressing process uses a cylindrical graphite cap for axial pressure. The cylindrical graphite cap has a height of 10 mm and a diameter of 22 mm. The graphite cap is placed on top of the graphite mold, and pressure is applied by an electric discharge plasma sintering device to improve the uniformity of stress on the pressing interface and the bonding quality of the interface.

5. The method for preparing a Co-Hf-Ta ternary diffusion couple according to any one of claims 1 to 4, characterized in that, The SPS pressing process in steps S2 and S3 is as follows: First, the temperature is raised from room temperature to 923 K at a heating rate of 100 K / min, and then raised to 1023 K at a heating rate of 50 K / min. An axial pressure of 30 MPa is applied at 1023 K and held for 10 min. Then, the furnace is cooled to room temperature.

6. The method for preparing the Co-Hf-Ta ternary diffusion couple according to claims 1 to 5, characterized in that, In steps S2 and S3, the grinding and polishing processes are carried out by mechanical grinding with sandpaper of different grit sizes and polishing with metallographic polishing paste to make the surface of the pressing interface smooth.

7. The method for preparing the Co-Hf-Ta ternary diffusion couple according to claims 1 to 6, characterized in that, The diffusion annealing time in step S4 is 20 to 40 days, preferably 30 days. Before annealing, the quartz tube containing the Co-Hf-Ta ternary press block is evacuated to a pressure not higher than 10⁻² Pa, then filled with argon gas and sealed. After annealing, it is immediately water quenched to preserve the phase structure formed in the high-temperature diffusion state.

8. The method for preparing the Co-Hf-Ta ternary diffusion couple according to claim 1, characterized in that: In step S5, the diffusion couple sample is cut and then subjected to metallographic mounting using a thermal mounting method. The thermal mounting uses thermosetting resin mounting powder to form a metallographic mounting sample under heating and pressure conditions. Subsequently, the mounting sample is ground and polished, and the cross-sectional microstructure of the diffusion couple is observed using a scanning electron microscope (SEM). Composition analysis is performed using electron probe microanalysis (EPMA).

9. A Co-Hf-Ta ternary diffusion couple, characterized in that, Prepared by the method described in any one of claims 1 to 8, the diffusion couple forms a continuous diffusion layer structure inside, and the elements Co, Hf and Ta are distributed in a continuous gradient along the diffusion direction.

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