| CVD(Chemical Vapor Deposition, CVD) diamond has many excellent properties similar to that of natural diamond, such as high hardness, low friction coefficient, low thermal expansion coefficient, high wear resistance and good chemical stability and so on. It is a good kind of wear resistance anti-friction coating material and its abrasion performance is 50 ~ 200 times than carbide’s. High speed steel material tool has high toughness, widely used in cutting tool industry in China. But its poor abrasion resistance to wear, causing the huge waste of resources. Therefore, depositing CVD diamond coating on the surface of high speed steel substrate can combine the advantages of both. And the using performance of high speed steel tools and its service life can be improved. The future of this technology is brilliant. However, depositing high quality of CVD diamond coating on the surface of high speed steel substrate directly faces some key technical difficulties such as low nucleation rate, low adhesion strength. So, in view of these key technical difficulties, main research content of this article is as follows:1. Proposed a novel CVD diamond coating pretreatment technology of W18Cr4 V high speed steel substrate. In order to solve the technical difficulties, gradient stress absorption of Ni-P/Cu composite intermediate layer is researched in this dissertation. The penetrating process of the graphitization elements onto the surface of matrix is forbidded by the Ni-P/Cu composite intermediate layer, and the diamond nucleation rate is also enhanced. The carbon produced by gas source is prevented to penetrating into the matrix by the Ni-P/Cu layer at the same time. And the residual stress produced in the growth and cooling processes of diamond coating can be absorbed effectively by soft Cu layer.2. Research on low temperature deposition CVD diamond coatings technology. Diamond coating is prepared by HFCVD method. To reducing the temperature of the substrate by improving the flow of reaction gas, reducing the thermal stress of coating by reasonable control the temperature of the reaction chamber. Deposition parameters have important influence on the properties of diamond coating. Through four group contrast tests were conducted to study effects of deposition pressure, gas flow ratio, temperature, and pretreatment to CVD diamond coating. The structure, surface morphology, adhesion strength and other performance characterization of CVD diamond coatings were tested by Scanning electron microscopy, Raman spectroscopy, XRD diffraction, Rockwell hardness. The optimum deposition parameters abstract from these tests were deposition pressure of 4 k Pa, temperature of 450 ℃, hydro-carbon gas flow ratio of 30/300, bias current of 1.5 A, distance between wire and matrix of 9-10 mm. The electroless plating 2.5 h and electroplating 10 min Ni-P/Cu composite intermediate layer has high purity, good adhesive strength of diamond coating. Moreover, electroless plating 2.5 h Ni-P monolayer also got a diamond coating with high surface quality.3. The tribological properties of CVD Diamond with different intermediate layers were evaluated by using ball-bearing steel and Cu as counterpart materials. The results of SEM images indicate that the friction and wear properties of CVD diamond coating have great difference between ball-bearing steel and Cu as friction counterparts. The coefficient of friction of copper counterpart is larger than ball-bearing steel’s. And there is not only abrasive wear exists on the surface of Cu counterpart, but also adhesive wear serious exists at the same time. But there is only abrasive wear occurs obviously on the surface of ball-bearing steel counterpart; when the material of friction counterparts is the same. Thanks to its uniform size and low surface roughness, the coefficient of friction of the Ni-P monolayer with CVD diamond coating is smaller than the Ni-P/Cu composition intermediate layer. But the coating will wear in a relatively short period of time due to the weakness of adhesion strength between diamond coating and Ni-P coating. |
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