A method for plating diamond surfaces with the intermetallic compound Ni3Al

Abstract

The application discloses a method for plating Ni3Al intermetallic compound on a diamond surface and belongs to the technical field of diamond surface metallization treatment. The method comprises the following steps: mechanically alloying Ni, Al and alloy element powders by high-energy ball milling to obtain nickel-based alloyed powder; mixing the alloyed powder and surface cleaning pretreated diamond according to a proportion, placing the mixture in a crucible, covering NaCl-KCl mixed salt, and heating to 950-1050 DEG C under argon protection in a program-controlled temperature mode to perform molten salt bath plating. The application expands the stable existing interval of Ni3Al ordered phase and reduces the synthesis temperature by using Co, Ti, Mo, W and other alloy elements, promotes the solid phase diffusion reaction between the pre-alloyed powder and the diamond surface by taking molten salt as a liquid phase medium, and generates a plating layer mainly composed of Ni3Al ordered phase on the diamond surface in situ. The method is simple in process, low in cost and suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of diamond surface modification technology, specifically relating to a method for coating a diamond surface with a Ni3Al intermetallic compound. Background Technology

[0002] Diamond possesses extremely high hardness, the highest thermal conductivity, extremely low coefficient of thermal expansion, and excellent chemical stability and wear resistance, making it an ideal reinforcing phase and functional material for preparing high-performance grinding tools, cutting tools, electronic packaging thermal management composites, and wear-resistant components. However, there is an inherent interfacial incompatibility between diamond and most metal matrices: diamond has extremely high surface energy and strong chemical inertness, and its wetting angle with molten metal is usually greater than 90°. The interfacial bonding relies solely on weak physical interlocking caused by cooling contraction, leading to diamond particles being easily detached during service. This results in extremely high interfacial thermal resistance, preventing the full utilization of its excellent thermal conductivity and mechanical properties.

[0003] To address the challenge of interfacial bonding between diamond and metal substrates, diamond surface metallization is currently the most mainstream technological approach. The basic principle involves pre-coating the diamond surface with a metal or alloy layer containing strong carbide-forming elements. These elements then react with the carbon atoms on the diamond surface at high temperatures, generating an in-situ metal carbide transition layer. This transforms the originally non-wetting diamond-metal interface into a wettable diamond-carbide-metal gradient chemically bonded interface. Common coating methods include chemical vapor deposition (CVD), physical vapor deposition (PVD), magnetron sputtering, electroless plating, electroplating, and molten salt plating. Among these, molten salt plating has been widely used in recent years for coating carbide layers (such as TiC, Cr3C2, WC, etc.) on diamond surfaces due to its simple equipment, convenient operation, low cost, and suitability for batch processing.

[0004] Ni3Al is an intermetallic compound with an L12 ordered face-centered cubic structure (γ' phase). Due to its excellent high-temperature strength, unique yield strength-temperature anomalous effect, good oxidation resistance, and corrosion resistance, it is considered an ideal coating material for metallizing diamond surfaces. However, the direct coating of Ni3Al onto diamond surfaces faces the following technical obstacles:

[0005] First, the synthesis of Ni3Al, as an ordered face-centered cubic γ' phase, is inherently challenging. This ordered phase has a high initial formation temperature; without the addition of other alloying elements, a temperature above 1300℃ is typically required to obtain a fully ordered Ni3Al phase through a diffusion-type phase transformation. If the temperature is insufficient or the composition deviates, a disordered face-centered cubic γ phase is easily formed, failing to achieve the desired L12 ordered structure. Therefore, it is necessary to add appropriate alloying elements to lower the initial formation temperature of the ordered Ni3Al phase and expand its stable existence range in the phase diagram.

[0006] Secondly, conventional vapor deposition methods (such as chemical vapor deposition and physical vapor deposition) are difficult to directly prepare Ni3Al ordered phase coatings on diamond surfaces. This is because the vapor deposition process decomposes the source material into individual atoms or molecules, which are then deposited one by one onto the substrate surface and condensed into a film. For Ni3Al, only elemental atoms such as Ni and Al are deposited on the diamond surface, and these elemental atoms do not possess an L12 ordered structure. To form an ordered Ni3Al phase, subsequent high-temperature heat treatment is necessary to allow Ni and Al atoms to undergo long-range diffusion and ordered rearrangement in the solid state. However, diamond has a tendency to graphitize at high temperatures, and the degree of interfacial reaction is difficult to control precisely during heat treatment. Therefore, relying solely on vapor deposition followed by heat treatment makes it difficult to obtain a uniform and continuous Ni3Al ordered phase coating on the diamond surface.

[0007] Currently, there are very few reports, both domestically and internationally, on the direct deposition of Ni3Al ordered phase coatings on diamond surfaces. The molten salt bath method employed in this invention provides an effective solution to these problems. In the process of this invention, the deposition temperature (950~1050℃) is lower than the melting point of the metal powder. The molten salt (a mixture of NaCl and KCl) is in a liquid phase at this temperature, and its main function is to act as a liquid medium to wet and fill the spaces between metal powder particles, making it easier for the metal particles to contact the diamond surface in the liquid environment, providing an efficient mass transfer channel for element diffusion and interfacial reactions. Simultaneously, the elements in the pre-alloyed nickel-based powder prepared by ball milling have been fully dissolved at the atomic scale. When the powder is in close contact with the diamond surface in the molten salt medium, a Ni3Al ordered phase coating can be generated in situ on the diamond surface at a lower temperature through a solid-phase diffusion reaction. The addition of alloying elements not only lowers the synthesis temperature of the ordered phase and stabilizes the γ' phase region, but also improves the coating quality by controlling the formation behavior of interfacial carbides, ultimately obtaining a fully covered and well-crystallized Ni3Al ordered phase coating. Summary of the Invention

[0008] The purpose of this invention is to provide a method for coating a diamond surface with a Ni3Al intermetallic compound. The principle involves preparing a nickel-based alloy ball-milled powder by mechanically alloying nickel powder, aluminum powder, and alloying element powders such as Co, Cr, Ti, Mo, and W. Then, using NaCl-KCl molten salt as the liquid phase medium, the pre-alloyed powder reacts with the diamond surface at 950-1050°C through a solid-phase diffusion reaction to generate an ordered Ni3Al phase coating in situ. Using the method provided by this invention, a complete and well-crystallized Ni3Al coating can be formed on the diamond surface.

[0009] This invention provides a method for coating a diamond surface with a Ni3Al intermetallic compound, comprising the following steps:

[0010] (1) Powder preparation: The metal powders according to the composition ratio are subjected to high-energy ball milling under an inert atmosphere to fully dissolve the alloying elements in the nickel matrix and obtain nickel-based alloy ball milled powder with uniform composition.

[0011] (2) Surface pretreatment of diamond: The single crystal diamond particles are acid-washed and alkali-washed to remove surface oil and impurities. After each cleaning, they are ultrasonically cleaned with alcohol and then dried.

[0012] (3) Co-deposition of Ni3Al coating by molten salt bath: The nickel-based alloy ball milled powder obtained in step (1) and the single crystal diamond obtained in step (2) are mixed in proportion and placed in an alumina crucible. A mixed salt of sodium chloride and potassium chloride is placed on the mixed powder. The crucible is placed in a tube furnace and heated to the target temperature under a protective atmosphere and held at the temperature by programmed temperature control. After the holding period, the furnace is cooled. Then, the molten salt is removed by water bath immersion. After drying, the product is sieved to obtain diamond particles with Ni3Al coating on the surface.

[0013] Step (1) specifically includes: the composition ratio of the nickel-based alloy ball milling powder is: Cr 0.2~6wt%, Co 6.5~7.2wt%, Ti 0.1~2wt%, Mo 2.8~4wt%, W 1.9~2wt%, Al 9.4~12.4wt%, with the balance being Ni; wherein, the amount of aluminum added is in the ratio of Ni to Al atomic ratio of (3~4):1; the above metal powder is loaded into a high-energy ball mill, protected by high-purity argon gas, and ball milled at a speed of 150~200r / min for 24~30h, and the alloying elements are fully dissolved in the nickel matrix through mechanical alloying to obtain a nickel-aluminum pre-alloyed powder with uniform composition.

[0014] Step (2) specifically includes: acid and alkali washing treatment of single crystal diamond, which involves first immersing the single crystal diamond particles in 2.8~3 mol / L sodium hydroxide solution and 9.8~10 mol / L hydrochloric acid solution, and ultrasonically cleaning for 20~30 min each time. After each chemical cleaning, the particles are rinsed with deionized water until neutral, and then ultrasonically cleaned with anhydrous ethanol for 10~15 min. Finally, the particles are vacuum dried at 80~120℃ for 2~4 h to obtain single crystal diamond with a clean surface.

[0015] Step (3) specifically includes: first, mixing sodium chloride and potassium chloride at a mass ratio of (0.8~1.2):1 to obtain a mixed salt as the molten salt medium; loading the single crystal diamond obtained in step (2) and the nickel-based alloy ball milling powder obtained in step (1) into the alumina crucible at a mass ratio of (8~12):1; then covering the mixed powder with the sodium chloride-potassium chloride mixed salt for loading, with the mass ratio of the nickel-based alloy ball milling powder and diamond mixture to the mixed salt being 1:(1.5~3); subsequently placing the crucible in a tube furnace, continuously introducing argon gas at a flow rate of 0.2~0.4L / min as a protective atmosphere, and performing programmed temperature control: first heating to 100℃ at a heating rate of 5℃ / min, and holding at that temperature for 1 minute. The process involves heating the powder at 0-20 min to remove moisture from the salt and prevent molten salt from splashing. Then, the temperature is increased to 600℃ at 5℃ / min and held for 20-30 min to promote pre-reaction of the powder. Next, the temperature is increased to the target temperature of 950-1050℃ at 5℃ / min and held for 20-80 min. After holding, the temperature is reduced from the target temperature to 500℃ at a rate of 5℃ / min, and then allowed to cool naturally to room temperature. The extracted blocky product is repeatedly washed 3-5 times with boiling deionized water for 10-30 min each time to fully dissolve and remove solidified sodium chloride and potassium chloride. Finally, the product is filtered and dried at 80-120℃ for 2-4 h. After sieving, diamond particles coated with a Ni3Al layer are obtained.

[0016] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0017] (1) By synergistically adding alloying elements such as Co, Ti, Mo, and W to nickel-based alloy powder, the present invention effectively reduces the initial formation temperature of the ordered phase (γ' phase) of Ni3Al, and reduces the synthesis temperature from the usually required 1300℃ or more to 950~1050℃.

[0018] (2) In the Ni3Al ordered phase coating, Co can replace some of the Ni lattice positions in Ni3Al, stabilizing the γ' ordered phase over a wide temperature range. Elements such as Ti, Mo, and W have a certain solid solubility in Ni3Al and tend to occupy Al sublattice positions. After these elements replace Al, they form stronger chemical bonds with the surrounding Ni atoms, improving the thermodynamic stability of the L12 ordered structure. This can effectively expand the stable existence range of the γ' phase in the phase diagram, increase the order-disorder transition temperature, and thus suppress the transformation of the γ' phase to the disordered γ phase over a wide temperature range, promoting the formation and stabilization of the Ni3Al ordered phase. This makes it possible to directly obtain an ordered Ni3Al coating on the diamond surface through solid-phase diffusion reaction, solving the technical problem that conventional methods cannot directly prepare Ni3Al ordered phase coatings on the diamond surface.

[0019] (3) This invention employs a molten salt bath method, using a NaCl-KCl mixed salt as the liquid phase medium. At the plating temperature, the metal powder does not melt entirely. The molten salt wets and fills the spaces between the powder particles, making it easier for the pre-alloyed powder to contact the diamond surface in the liquid phase environment, providing an efficient mass transfer channel for solid-phase diffusion and interfacial reactions. This method is simple to operate, has low equipment cost and low energy consumption, and the prepared Ni3Al-plated diamond particles have a complete coating layer that bonds well with the diamond matrix, showing promising application prospects. Attached Figure Description

[0020] Figure 1 This is a SEM image of the Ni3Al-plated diamond particles obtained in Example 1.

[0021] Figure 2 This is an EDS image of the (111) surface of the Ni3Al-plated diamond particles obtained in Example 1.

[0022] Figure 3 The images show XRD patterns (a) and magnified views (b) of the Ni3Al-plated diamond particles obtained in Examples 1-6.

[0023] Figure 4 The images show XRD patterns (a) and magnified views (b) of the Ni3Al-plated diamond particles obtained in Examples 7-9.

[0024] Figure 5 The images are XRD patterns (a) and magnified views (b) of the Ni3Al-plated diamond particles obtained in Examples 10-13.

[0025] Figure 6 The images show the XRD patterns (a) and magnified views (b) of the Ni3Al-plated diamond particles obtained in Comparative Examples 1 and 2. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0027] Example 1

[0028] (1): Weigh out metal powder with the following mass percentages: Co 7.08%, Cr 6.00%, Mo 2.83%, W 1.90%, Ti 1.21%, Al 10.76%, and the balance being Ni (Ni to Al atomic ratio 3:1). Place all the above metal powder into a stainless steel ball mill jar with a ball-to-powder mass ratio of 10:1, seal, and evacuate to 1000 kcal / min. -2 Below Pa, backfill with high-purity argon to a slightly positive pressure, repeating this process three times. Place the ball mill jar on a planetary high-energy ball mill and ball mill at 150 r / min for 24 h. After ball milling, open the jar in an argon-protected glove box, remove the powder, and pass it through a 200-mesh sieve to obtain mechanically alloyed nickel-based alloy ball mill powder.

[0029] (2): 10g of commercially available diamond particles with a particle size of 125~150µm were placed in 100mL of 9.8mol / L hydrochloric acid aqueous solution and ultrasonically cleaned for 30min. They were then rinsed with deionized water until neutral and ultrasonically cleaned with anhydrous ethanol for 10min. Next, they were placed in 100mL of 2.8mol / L sodium hydroxide aqueous solution and ultrasonically cleaned for 30min. They were then rinsed with deionized water until neutral and ultrasonically cleaned with anhydrous ethanol for 10min. Finally, they were vacuum dried at 80℃ for 2h to obtain clean single crystal diamond, which was then sealed and stored for later use.

[0030] (3): The nickel-based alloy ball milled powder obtained in step (1) is mixed with the single-crystal diamond particles obtained in step (2), with a mass ratio of diamond to nickel-based alloy ball milled powder of 10:1. The mixed powder is placed in an alumina crucible, and then a sodium chloride-potassium chloride mixed salt is placed on top of the mixed powder, with a mass ratio of mixed salt to mixed powder of 2:1. The crucible is placed in a tube furnace and evacuated to 10 °C. -3 Below Pa, the protective atmosphere consisted of a continuous flow of argon gas at a rate of 0.3 L / min. The temperature was increased from room temperature to 100°C at a rate of 5°C / min and held for 10 min to remove residual moisture from the salt. Subsequently, the temperature was increased to 600°C at a rate of 5°C / min and held for 20 min to promote pre-reaction of the powder. The temperature was then increased to 950°C at a rate of 5°C / min and held for 60 min. After the holding period, the temperature was first reduced to 500°C at a rate of 5°C / min, and then cooled to room temperature with the furnace. The blocky product was removed from the crucible and repeatedly rinsed three times with boiling deionized water to fully dissolve and remove sodium chloride and potassium chloride. After filtration, it was dried at 80°C for 2 h, and sieved to obtain diamond particles coated with a Ni3Al composite layer.

[0031] Example 2

[0032] The only difference from Example 1 is that the sintering temperature in step (3) is changed to 1000°C.

[0033] Example 3

[0034] The only difference from Example 1 is that the sintering temperature in step (3) is changed to 900°C.

[0035] Example 4

[0036] The only difference from Example 1 is that the heat preservation time in step (3) is changed to 20 min.

[0037] Example 5

[0038] The only difference from Example 1 is that the heat preservation time in step (3) is changed to 40 min.

[0039] Example 6

[0040] The only difference from Example 1 is that the heat preservation time in step (3) is changed to 80 min.

[0041] Example 7

[0042] The only difference from Example 1 is that in step (1), the amount of aluminum powder added is prepared according to the atomic ratio of Ni to Al of 4:1 (after adjustment, the mass percentage of Al is about 9.9%, and only the mass percentage of Ni is adjusted simultaneously).

[0043] Example 8

[0044] The only difference from Example 1 is that in step (1), the amount of aluminum powder added is prepared according to the atomic ratio of Ni to Al of 2:1 (after adjustment, the mass percentage of Al is about 18.5%, and only the mass percentage of Ni is adjusted simultaneously).

[0045] Example 9

[0046] The only difference from Example 1 is that in step (1), the amount of aluminum powder added is prepared according to the atomic ratio of Ni to Al of 1:1 (after adjustment, the mass percentage of Al is about 31.5%, and only the mass percentage of Ni is adjusted simultaneously).

[0047] Example 10

[0048] The only difference from Example 1 is that the Cr content in step (1) is adjusted to 1wt%, and metal powder is weighed according to the mass percentages of Co 7.16%, Cr 1.00%, Mo 2.86%, W 1.92%, Ti 1.22%, Al 10.88%, with the balance being Ni.

[0049] Example 11

[0050] The only difference from Example 1 is that the Cr content in step (1) is adjusted to 3wt%, and metal powder is weighed according to the mass percentages of Co 7.12%, Cr 3.00%, Mo 2.84%, W 1.91%, Ti 1.22%, Al 10.82%, with the balance being Ni.

[0051] Example 12

[0052] The only difference from Example 1 is that the Ti content in step (1) is adjusted to 1 wt%, and metal powder is weighed according to the mass percentages of Co 7.82%, Cr 1.09%, Mo 4.00%, W 2.10%, Ti 1.00%, Al 11.88%, with the balance being Ni.

[0053] Example 13

[0054] The only difference from Example 1 is that the Ti content in step (1) is adjusted to 2wt%, and metal powder is weighed according to the mass percentages of Co 7.16%, Cr 1.00%, Mo 2.86%, W 1.92%, Ti 2.00%, Al 10.88%, with the balance being Ni.

[0055] Comparative Example 1

[0056] The only difference from Example 1 is that the sintering temperature in step (3) is changed to 850°C.

[0057] Comparative Example 2

[0058] The only difference from Example 1 is that the Cr content in step (1) is adjusted to 0.1wt%, and metal powder is weighed according to the mass percentages of Co 7.18%, Cr 0.10%, Mo 2.87%, W 1.93%, Ti 1.23%, Al 10.92%, with the balance being Ni.

[0059] The Ni3Al-coated diamond particles prepared in Example 1 were analyzed by scanning electron microscopy and energy dispersive spectroscopy. The results are as follows: Figure 1 As shown. Figure 1 The coating material is uniformly and continuously covering the surface of the diamond particles, with no obvious exposed diamond matrix areas, indicating that the coating has good integrity. SEM morphology at different magnifications shows that the coating surface is composed of a large number of micron-sized particle protrusions and their aggregates, exhibiting typical island-like nucleation and growth characteristics; the island protrusions overlap and are tightly bonded to each other.

[0060] Figure 2 The EDS results shown further indicate that the relevant elements in the coating area are significantly enriched on the particle surface, indicating that the coating has been successfully deposited on the diamond surface.

[0061] Table 1. Phase content of diamond coatings prepared in each example and comparative example.

[0062] sample <![CDATA[γ' phase (L12)]]> <![CDATA[β-phase (B2)]]> <![CDATA[Cr3C2]]> γ phase (FCC) <![CDATA[Mo2C]]> Example 1 95.17% - 2.03% 2.80% - Example 2 92.33% - 1.16% 6.51% - Example 3 88.99% - - 11.01% - Example 4 88.45% - 1.99% 9.56% - Example 5 80.92% - 8.56% 10.52% - Example 6 73.58% - 4.87% 16.55% - Example 7 89.37% - 0.92% 9.71% - Example 8 69.20% 15.60% 10.99% 4.21% - Example 9 - 94.50% 4.85% 5.65% - Example 10 92.20% - - 7.05% 0.75% Example 11 93.17% - - 5.63% 1.20% Example 12 96.35% - - 1.96% 1.69% Example 13 96.15% - - 2.40% 1.45% Comparative Example 1 78.36% - - 18.41% 3.23% Comparative Example 2 83.66% - - 14.31% 2.03%

[0063] The Ni3Al-coated diamond particles prepared in Examples 1-13 and Comparative Examples 1-2 were characterized by XRD and quantitative phase analysis was performed. The results of the quantitative phase analysis are listed in Table 1, and the corresponding XRD patterns are shown in the figure. Figures 3-6 As shown.

[0064] Figure 3 The XRD patterns of coatings obtained under different heat preservation times and temperatures are shown in Table 1. Figure 3 It can be seen that in Examples 1-3, crystalline coatings with Ni3Al as the main phase can be successfully generated in the temperature range of 900-1000℃, with Ni3Al content of 88.99%-95.17% and γ phase content of 2.80%-11.01%; in Examples 1 and Examples 4-6, Ni3Al content is 73.58%-95.17% and γ phase content is 2.80%-16.55%; in Example 1, the Ni3Al diffraction peak intensity and content are the highest at 60 min, indicating that 60 min is the optimal holding time.

[0065] Figure 4 The XRD patterns of the coatings obtained under different Ni:Al atomic ratios are shown in Table 1. According to the data in Table 1, in Examples 1 and 7, when the Ni:Al atomic ratios were 3:1 and 4:1 respectively, the Ni3Al content was 95.17% and 89.37%, and the γ phase content was 2.80% and 9.71% respectively, both yielding coatings with Ni3Al as the main phase. When the Ni:Al atomic ratio decreased to 2:1, the Ni3Al content decreased to 69.20%, and 15.60% of the β phase (NiAl) appeared. Further decreasing to 1:1, the Ni3Al phase completely disappeared, and the main phase transformed into 94.50% of the β phase (NiAl). These results indicate that a Ni:Al ratio deviating too much from 3:1 significantly inhibits the formation of the ordered Ni3Al phase. Therefore, the preferred Ni:Al atomic ratio is (3~4):1.

[0066] Figure 5 The XRD patterns of coatings obtained under different Ti / Cr ratios are shown in Table 1. Figure 5As can be seen, clear and complete Ni3Al characteristic diffraction peaks appeared in all embodiments. When the Cr content varied from 1% to 6%, the Ni3Al content was 92.20% to 96.35%, the γ phase content was 1.96% to 7.05%, and the Cr3C2 content gradually decreased until it disappeared as the Cr content decreased. When the Ti content varied from 1.00% to 2.00%, the Ni3Al content in Examples 12 and 13 reached 96.35% and 96.15%, respectively, and the γ phase content decreased to 1.96% and 2.40%, respectively, which were the groups with the highest Ni3Al content among all embodiments.

[0067] Figure 6 No obvious Ni3Al diffraction peaks were detected in the XRD pattern of Comparative Example 1. Combined with the fact that the Ni3Al content of Comparative Example 1 in Table 1 was only 78.36% and the γ phase content was as high as 18.41%, it is confirmed that the temperature of 850℃ is too low and cannot achieve the synthesis of a large number of Ni3Al ordered phases. Figure 6 The XRD pattern of Comparative Example 2 further shows that when the Cr content drops to 0.1%, the Cr3C2 diffraction peak disappears completely, but at this time the Ni3Al content drops to 83.66% and the γ phase content rises to 14.31%, indicating that too low a Cr content is not conducive to the full formation of the Ni3Al ordered phase.

[0068] The above results indicate that the formation and stabilization of the Ni3Al ordered phase are mainly determined by the synergistic effect of γ' phase stabilizing elements such as Ti, Co, Mo, and W. The content of each element needs to be controlled within an appropriate range in order to obtain a high-quality coating dominated by the Ni3Al ordered phase.

Claims

1. A method for coating a diamond surface with a Ni3Al intermetallic compound, characterized in that, Includes the following steps: (1) Powder preparation: The metal powders according to the composition ratio are subjected to high-energy ball milling under an inert atmosphere to fully dissolve the alloying elements in the nickel matrix and obtain nickel-based alloy ball milled powder with uniform composition. (2) Surface pretreatment of diamond: The single crystal diamond particles are acid-washed and alkali-washed to remove surface oil and impurities. After each cleaning, they are ultrasonically cleaned with alcohol and then dried. (3) Co-deposition of Ni3Al coating by molten salt bath: The nickel-based alloy ball milled powder obtained in step (1) and the single crystal diamond obtained in step (2) are mixed in proportion and placed in an alumina crucible. A mixed salt of sodium chloride and potassium chloride is covered on the mixed powder. The crucible is placed in a tube furnace and heated to the target temperature in a protective atmosphere and kept at the temperature by programmed temperature control. After the heat preservation is completed, the material is cooled with the furnace, then washed with a water bath to remove the molten salt, dried, and sieved to obtain diamond particles with a Ni3Al coating on the surface.

2. The method as described in claim 1, characterized in that, In step (1), the composition ratio of the metal powder is: Cr 0.2~6wt%, Co 6.5~7.2wt%, Ti 0.1~2wt%, Mo 2.8~4wt%, W 1.9~2wt%, Al 9.4~12.4wt%, with the balance being Ni.

3. The method as described in claim 1, characterized in that, In step (1), the atomic ratio of Ni to Al is (3~4):

1.

4. The method as described in claim 1, characterized in that, In step (1), the high-energy ball milling speed is 150~200 r / min, the ball milling time is 24~30 h, and high-purity argon gas is introduced for protection during the ball milling process, so that aluminum and other alloying elements are mechanically alloyed in the nickel matrix to obtain nickel-based alloy ball milling powder with uniform composition.

5. The method as described in claim 1, characterized in that, In step (2), the acid and alkali washing treatment of single crystal diamond is as follows: diamond particles are placed in 2.8~3 mol / L sodium hydroxide solution and 9.8~10 mol / L hydrochloric acid solution in sequence, and ultrasonically cleaned for 20~30 min each time. After each chemical cleaning, they are rinsed with deionized water until neutral, and then ultrasonically cleaned with anhydrous ethanol for 10~15 min. Finally, they are vacuum dried at 80~120℃ for 2~4 h to obtain single crystal diamond with a clean surface.

6. The method as described in claim 1, characterized in that, In step (3), the mass ratio of sodium chloride to potassium chloride in the mixed salt is (0.8~1.2):1, the mass ratio of single crystal diamond to nickel-based alloy ball milling powder is (8~12):1, and the mixed powder and mixed salt are loaded at a mass ratio of 1:(1.5~3). The loading method is as follows: first, the uniform mixture of nickel-based alloy ball milling powder and single crystal diamond is placed at the bottom of the alumina crucible and moderately compacted or leveled. Then, the pre-mixed sodium chloride-potassium chloride mixed salt is poured over the mixed powder so that the mixed salt layer completely covers the mixed powder below, forming a layered loading structure from bottom to top consisting of a mixed powder layer and a mixed salt layer.

7. The method as described in claim 1, characterized in that, In step (3), the protective atmosphere is argon gas continuously introduced at a flow rate of 0.2~0.4 L / min. The temperature rise rate of the programmed temperature control is 5℃ / min. First, the temperature is raised to 100℃ and held for 10~20 min to remove moisture from the salt and prevent molten salt from splashing. Then, the temperature is raised to 600℃ and held for 20~30 min to promote the pre-reaction of the powder. Then, the temperature is raised to the target temperature of 950~1050℃ and held for 20~80 min. After the holding time is completed, the temperature is lowered from the target temperature to 500℃ at a programmed cooling rate of 5℃ / min. Then, the furnace is cooled to room temperature.

8. The method as described in claim 1, characterized in that, In step (3), the water bath washing is specifically as follows: the product is repeatedly washed with boiling deionized water 3 to 5 times, each time for 10 to 30 minutes, to fully remove solidified sodium chloride and potassium chloride. Then it is filtered and dried at 80 to 120°C for 2 to 4 hours. Finally, diamond particles with Ni3Al coating on the surface are obtained by sieving.

9. Diamond particles with a Ni3Al coating on their surface prepared by the method according to any one of claims 1 to 8, characterized in that, The phase composition of the coating, by mass percentage, is as follows: γ' phase (L12) 69.20%~96.35%, γ phase (FCC) 1.96%~18.41%, Cr3C2 0~10.99%, Mo2C 0~3.23%.

Images