Diamond surface diffusion chromium plating method

Abstract

The invention relates to the technical field of film plating, in particular to a diamond surface diffusion chromium plating method. The preparation method comprises the following steps: mixing diamond powder with chromium powder to obtain mixed powder; the mixed powder is subjected to spark plasma sintering, the chromium element reacts and diffuses on the surfaces of the diamond particles, and a chromium coating with the composition of Cr3C2 is formed; the spark plasma sintering temperature ranges from 850 DEG C to 900 DEG C, the axial pressure ranges from 10 MPa to 40 MPa, and the heat preservation time ranges from 30 min to 90 min. According to the method, heat preservation is conducted in the SPS equipment, reaction diffusion of the chromium element on the surfaces of diamond particles is achieved, in the SPS sintering process, the mixed powder is under the combined action of a temperature field, a pressure field and a current field, the heat activation temperature needed by the diffusion reaction can be effectively reduced, the diffusion speed of chromium atoms to the surface layer of the diamond is increased, and the diffusion efficiency is improved. And graphitization of the diamond is effectively inhibited, and finally the uniform chromium plating layer which is good in quality and compactly combined with the diamond is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of film coating, and in particular to a method for diffusion chromium plating on a diamond surface. Background Art

[0002] Diamond combines ultra-high hardness, excellent wear resistance, outstanding chemical stability, and unique optical, acoustic, thermal and electrical properties, and is regarded as one of the highest performance engineering materials.

[0003] In order to achieve effective bonding of diamond particles with various metal matrices (such as tool bodies, composite matrices, etc.) and fully unleash their superhard properties and functional advantages, it is usually necessary to perform metallization treatment on their surface.

[0004] Among the many metal coatings, chromium coatings have attracted considerable attention due to their exceptional hardness, outstanding wear resistance, and superior resistance to high-temperature oxidation and corrosion. For specific high-performance applications, such as extremely wear-resistant tools and high-temperature service components, achieving a dense, firmly bonded chromium layer on the diamond surface has significant technical and economic value. High-quality chromium coatings not only effectively protect the diamond surface but also form a strong metallurgical bond with the substrate, fully synergizing the combined performance advantages of diamond and chromium coatings. Therefore, the development of advanced and reliable processes for chromium plating on diamond surfaces is crucial.

[0005] The current development of chromium plating technology on diamond surfaces still faces severe challenges. The primary technical issue is the difficulty in effectively constructing a high-quality chromium coating on the diamond surface that combines high bonding strength with sufficient interfacial diffusion. Chromium layers obtained by traditional processes (such as electroplating and chemical chromium plating) generally lack interfacial bonding strength with the diamond substrate. Essentially, they rely primarily on mechanical anchoring or weak physical adsorption, rather than stable metallurgical or chemical bonding, resulting in the interface becoming a weak link during service. Thermal diffusion chromium plating can theoretically improve the bonding strength between the chromium coating and diamond, but thermal diffusion chromium plating often requires a strong thermal activation process (such as high-temperature, long-term annealing). This process directly induces a sharp contradiction in materials science: the inherent thermodynamic metastable properties of diamond make it extremely susceptible to irreversible graphitization phase transition (chemical formula: C(diamond) → C(graphite)) at high temperatures. This graphitization reaction not only severely degrades diamond's inherent core properties such as excellent hardness and thermal conductivity, but also directly destroys the integrity and bonding strength of the coating interface.

[0006] Therefore, how to achieve sufficient diffusion and strong bonding of chromium atoms at the interface while ensuring the stability of the diamond structure (inhibiting graphitization) is a fundamental scientific obstacle restricting the application of high-performance diamond / chromium composites. Summary of the Invention

[0007] In view of this, the object of the present invention is to provide a method for diffusion chromium plating on the surface of diamond. The method provided by the present invention can maintain the stability of the diamond structure under the premise of forming a strong bond between the chromium plating layer and the diamond.

[0008] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0009] The present invention provides a method for diffusion chromium plating on a diamond surface, comprising the following steps:

[0010] mixing diamond powder and chromium powder to obtain a mixed powder;

[0011] The mixed powder is subjected to spark plasma sintering, and the chromium element reacts and diffuses on the surface of the diamond particles to form a chromium coating composed of Cr3C2; the spark plasma sintering temperature is 850-900°C, the axial pressure is 10-40MPa, and the holding time is 30-90min.

[0012] Preferably, the spark plasma sintering temperature is 850°C.

[0013] Preferably, the average particle size of the diamond powder is 60-400 μm.

[0014] Preferably, the average particle size of the chromium powder is 1-20 μm.

[0015] Preferably, the volume ratio of the diamond powder to the chromium powder is 70-90:30-10.

[0016] Preferably, before mixing the diamond powder with the chromium powder, the diamond powder is pretreated; the pretreatment comprises placing the diamond powder in acetone, NaOH solution and HNO3 solution in sequence, performing ultrasonic treatment, washing with water and then drying.

[0017] Preferably, the rate of heating to the spark plasma sintering temperature is 50-100° C. / min.

[0018] Preferably, after the spark plasma sintering is completed, the power supply is cut off to allow the sintered powder to cool to room temperature.

[0019] Preferably, after the powder after spark plasma sintering is cooled to room temperature, the unreacted chromium powder is removed.

[0020] Preferably, the mixing is performed using a V-type mixer.

[0021] The present invention provides a method for diffusion chromium plating on a diamond surface, comprising the following steps: mixing diamond powder and chromium powder to obtain a mixed powder; subjecting the mixed powder to spark plasma sintering, so that chromium elements react and diffuse on the surfaces of diamond particles to form a chromium plating layer with a composition of Cr3C2; the spark plasma sintering temperature is 850-900°C, the axial pressure is 10-40MPa, and the holding time is 30-90min. In the present invention, in the initial stage of SPS sintering, the surface of the diamond is graphitized under the action of high temperature and electric field. At the same time, chromium elements diffuse on the surface of the diamond particles during the SPS sintering process. During the SPS sintering process, the mixed powder is subjected to the combined action of temperature field, pressure field and current field, which can effectively reduce the thermal activation temperature required for the diffusion reaction and increase the diffusion speed of chromium atoms to the diamond surface. The diffused chromium atoms quickly react with the graphite on the diamond surface to form stable Cr3C2. This layer serves as an effective diffusion barrier and protective layer, significantly inhibiting further conversion of the diamond interior to graphite. Ultimately, a uniform chromium plating layer (composed of Cr3C2) with good quality and densely bonded to the diamond is obtained, while maintaining the stability of the diamond structure.

[0022] In addition, compared with the prior art, the present invention also has the following beneficial effects:

[0023] The present invention utilizes the principle of reaction diffusion to generate a Cr3C2 coating by reacting chromium powder with carbon atoms on the diamond surface, thereby improving the oxidation resistance and graphitization performance of the diamond particles and the wettability of the diamond and the metal matrix, thereby contributing to the production of high-performance electronic packaging materials and wear-resistant materials.

[0024] Compared with the traditional thermal diffusion diamond coating process (without pressurization), the present invention also has the characteristics of low coating temperature, short coating time, simple process flow, easy control of parameters and stable quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 These are SEM photos of the chrome-plated diamond powders prepared in Examples 1-2 and Comparative Example 1;

[0026] Figure 2 The XRD characterization results of Examples 1-2, Comparative Example 1 and original diamond powder are shown;

[0027] Figure 3 TG-DSC test results of Examples 1-2, Comparative Example 1 and original diamond powder. DETAILED DESCRIPTION

[0028] The present invention provides a method for diffusion chromium plating on a diamond surface, comprising the following steps:

[0029] mixing diamond powder and chromium powder to obtain a mixed powder;

[0030] The mixed powder is subjected to spark plasma sintering, and the chromium element reacts and diffuses on the surface of the diamond particles to form a chromium coating composed of Cr3C2; the spark plasma sintering temperature is 850-900°C, the axial pressure is 10-40MPa, and the holding time is 30-90min.

[0031] In the present invention, the average particle size of the diamond powder is preferably 60-400 μm, and in specific embodiments, it can be 60 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, or 400 μm. The average particle size of the chromium powder is preferably 1-20 μm, and in specific embodiments, it can be 1 μm, 5 μm, 10 μm, 15 μm, or 20 μm. Controlling the particle size of the chromium powder within the above range facilitates both dispersion and subsequent removal by screening.

[0032] The present invention preferably pre-treats the diamond powder before mixing it with the chromium powder. In the present invention, the pre-treatment preferably includes: sequentially subjecting the diamond powder to ultrasonic treatment in acetone, a NaOH solution, and an HNO3 solution, followed by water washing and drying. In the present invention, the ultrasonic treatment time for the diamond powder in the acetone is preferably 20 minutes. The present invention removes organic matter from the surface of the diamond powder by ultrasonic treatment in acetone. In the present invention, the concentration of the NaOH solution is preferably 10 wt%, the ultrasonic treatment time in the NaOH solution is preferably 30 minutes, and the temperature of the NaOH solution is preferably 60°C. Oil stains from the surface of the diamond powder are removed by ultrasonic treatment in the NaOH solution. In the present invention, the concentration of the HNO3 solution is preferably 10 wt%, the ultrasonic treatment time in the HNO3 solution is preferably 30 minutes, and the temperature of the HNO3 solution is preferably 60°C. The present invention coarsens and activates the diamond powder by ultrasonic treatment in the HNO3 solution, thereby increasing its contact area with the chromium powder.

[0033] In the present invention, the volume ratio of the diamond powder to the chromium powder is preferably 70-90:30-10, and in specific embodiments may be 70:30, 80:20 or 90:10.

[0034] In the present invention, the mixing is preferably performed using a V-type mixer. The present invention has no particular requirements for the mixing conditions, as long as the diamond powder and chromium powder are uniformly mixed. In an embodiment of the present invention, the mixing tank of the V-type mixer is made of 304 stainless steel, and the mixing time is 5 hours.

[0035] After obtaining the mixed powder, the present invention performs spark plasma sintering on the mixed powder, and the chromium element reacts and diffuses on the surface of the diamond particles to form a chromium coating.

[0036] In the present invention, the spark plasma sintering temperature is 850-900°C, the axial pressure is 10-40 MPa, and the holding time is 30-90 minutes. In specific embodiments, the spark plasma sintering temperature can be 850°C, 860°C, 870°C, 880°C, 890°C, or 900°C; the axial pressure can be 10 MPa, 20 MPa, 30 MPa, or 40 MPa; and the spark plasma sintering holding time can be 30 minutes, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, or 90 minutes.

[0037] In the present invention, the rate of heating to the spark plasma sintering temperature is preferably 50-100°C / min, and in specific embodiments can be 50°C / min, 60°C / min, 70°C / min, 80°C / min, 90°C / min or 100°C / min.

[0038] In the present invention, in the initial stage of SPS sintering, the surface of the diamond is graphitized under the action of high temperature and electric field. At the same time, chromium elements diffuse on the surface of the diamond particles during the SPS sintering process. During the SPS sintering process, the mixed powder is subjected to the combined action of temperature field, pressure field and current field, which can effectively reduce the thermal activation temperature required for the diffusion reaction and increase the diffusion speed of chromium atoms to the diamond surface. The diffused chromium atoms quickly react with the graphite on the diamond surface to form stable Cr3C2. This layer serves as an effective diffusion barrier and protective layer, significantly inhibiting further conversion of the diamond interior to graphite. Ultimately, a uniform chromium plating layer (composed of Cr3C2) with good quality and densely bonded to the diamond is obtained, while maintaining a stable diamond structure.

[0039] After the spark plasma sintering is completed, the present invention preferably cuts off the power supply, allows the sintered powder to cool to room temperature, and then removes the unreacted chromium powder.

[0040] In the present invention, the unreacted chromium powder is preferably separated from the chromium-plated diamond by screening.

[0041] The following describes in detail a method for diffusion chromium plating on a diamond surface provided by the present invention in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0042] Example 1

[0043] Step 1: The diamond raw material powder was ultrasonically treated in acetone for 20 minutes to remove organic matter, then ultrasonically treated in a 10wt% NaOH solution at 60°C for 30 minutes to remove oil, and then ultrasonically cleaned in a 10wt% HNO3 solution at 60°C for 30 minutes to roughen the powder. The powder was then rinsed with deionized water and dried, and placed in a vacuum drying oven for later use.

[0044] Step 2: Diamond with an average particle size of 250 μm and chromium powder with an average particle size of 10 μm are mixed uniformly in a volume ratio of 90:10 using a V-type mixer;

[0045] Step 3: The mixed powder obtained in step 2 is heat treated by SPS technology, with a holding temperature of 850°C, a holding time of 60 minutes, and an axial pressure of 30 MPa;

[0046] Step 4: Mechanically sieve the reactants in step 3 to obtain chrome-plated diamond powder.

[0047] Example 2

[0048] The only difference from Example 1 is that the temperature of the SPS heat treatment in step 3 is 900°C.

[0049] Comparative Example 1

[0050] The only difference from Example 1 is that the temperature of the SPS heat treatment in step 3 is 800°C.

[0051] Comparative Example 2

[0052] The only difference from Comparative Example 1 is that the axial pressure is 0 MPa.

[0053] Visual observation showed that the coated diamonds retained their golden color, with no black Cr3C2 film visible. XRD analysis revealed no characteristic diffraction peaks of the Cr3C2 phase.

[0054] Comparative Example 3

[0055] The only difference from Example 1 is that the axial pressure is 0 MPa.

[0056] Visual observation showed that the coated diamonds retained their golden color, with no black Cr3C2 film visible. XRD analysis revealed no characteristic diffraction peaks of the Cr3C2 phase.

[0057] Characterization

[0058] The chromium-plated diamond powders prepared in Examples 1-2 and Comparative Example 1 were observed by scanning electron microscopy. Figure 1 shown. Figure 1In the figure, the first row is the SEM photographs after chromium plating at 800°C (Comparative Example 1), wherein (a) is a large-area SEM image, (a1) is a SEM image of the (100) crystal plane of one of the particles, and (a2) is a SEM image of the (111) crystal plane of one of the particles; the second row is the SEM photographs after chromium plating at 850°C (Example 1), wherein (b) is a large-area SEM image, (b1) is a SEM image of the (100) crystal plane of one of the particles, and (b2) is a SEM image of the (111) crystal plane of one of the particles; the third row is the SEM photographs after chromium plating at 900°C (Example 2), wherein (c) is a large-area SEM image, (c1) is a SEM image of the (100) crystal plane of one of the particles, and (c2) is a SEM image of the (111) crystal plane of one of the particles. Figure 1 The results show that the chromium coating on the diamond particles at 800°C is incomplete, with some uncoated areas. Plating at 850°C and 900°C provides better results, with relatively complete chromium coatings. However, the chromium coating at 900°C is thicker, with some cracking, and excessive thickness can affect the performance of diamonds. Overall, 850°C provides the best results.

[0059] XRD characterization was performed on Examples 1-2, Comparative Example 1 and the original diamond powder. The results are as follows: Figure 2 shown. Figure 2 In the graph, (a) is the original diamond powder, (b) is the comparative example 1 (800°C), (c) is the embodiment 1 (850°C), and (d) is the embodiment 2 (900°C). Figure 2 It can be seen that when SPS sintering is carried out at 800-900°C, no characteristic diffraction peak of graphite is detected in the chrome-plated diamond, indicating that no obvious graphitization occurs. This shows that the SPS chrome plating at 800-900°C in the present invention can maintain a stable diamond structure.

[0060] Examples 1-2 and Comparative Example 1 and the original diamond powder were subjected to TG-DSC test. The results are as follows: Figure 3 shown. Figure 3 In the graph, (a) is the original diamond powder, (b) is the comparative example 1 (800°C), (c) is the embodiment 1 (850°C), and (d) is the embodiment 2 (900°C). Figure 3 It can be seen that the graphitization and oxidation temperatures of the original diamond are 731°C and 768°C respectively, while the graphitization and oxidation temperatures of the chrome-plated diamond in Comparative Example 1 after chromium plating at 800°C are 746°C and 711°C respectively. The reason for the performance degradation is that at 800°C, the diffusion reaction is not sufficient. On the one hand, the graphite formed on the surface of the chrome-plated diamond during the SPS sintering process does not fully react with the Cr atoms (although some graphite does not react, the amount is small and cannot be detected by XRD). On the other hand, the Cr3C2 layer formed is very thin and discontinuous (such as Figure 1The incomplete coating has a low coverage rate and provides weak protection for the diamond core in subsequent TG tests. In Example 1, chromium plating at 850°C resulted in graphitization and oxidation temperatures of 753°C and 784°C, respectively, which are 22°C and 16°C higher than those of the original diamond. In Example 2, chromium plating at 900°C resulted in graphitization and oxidation temperatures of 758°C and 776°C, respectively, which are 27°C and 8°C higher than those of the original diamond.

[0061] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for diffusion chromium plating on a diamond surface, characterized in that: The following steps are involved: mixing diamond powder and chromium powder to obtain a mixed powder; The mixed powder is subjected to spark plasma sintering, and the chromium element reacts and diffuses on the surface of the diamond particles to form a chromium coating composed of Cr3C2; the spark plasma sintering temperature is 850-900°C, the axial pressure is 10-40MPa, and the holding time is 30-90min.

2. The method according to claim 1, characterized in that The spark plasma sintering temperature is 850°C.

3. The method according to claim 1, characterized in that The average particle size of the diamond powder is 60-400 μm.

4. The method according to claim 1, wherein The average particle size of the chromium powder is 1-20 μm.

5. The method according to claim 1, 3 or 4, characterized in that The volume ratio of the diamond powder to the chromium powder is 70-90:30-10.

6. The method according to claim 1, characterized in that Before mixing the diamond powder with the chromium powder, the diamond powder is pretreated; the pretreatment includes placing the diamond powder in acetone, NaOH solution and HNO3 solution in sequence, performing ultrasonic treatment, washing with water and then drying.

7. The method according to claim 1 or 2, characterized in that The rate of heating to the spark plasma sintering temperature is 50-100° C. / min.

8. The method according to claim 1, characterized in that After the spark plasma sintering is completed, the power supply is cut off to allow the sintered powder to cool to room temperature.

9. The method according to claim 8, characterized in that After the powder after spark plasma sintering is cooled to room temperature, the unreacted chromium powder is removed.

10. The method according to claim 1, characterized in that The mixing is performed using a V-type mixer.

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