Development Of WMoCr Polishing Plate Used In Dynamic Friction Polishing Of Diamond

Diamond possesses excellent physical, thermal, acoustics and optical properties resulting in its wide application, so the requirements for machining accuracy and surface quality of diamond are increasing. However, diamond is the difficult machining materials due to its highest hardness and excellent chemical inertness. There are many polishing technologies at present, such as mechanical polishing, thermo-chemical polishing, chemically assisted mechanical polishing, laser polishing, ion-beam polishing and so on. But there exist problems like low efficiency, poor surface quality, high cost, etc. Relatively lagged diamond polishing techniques are becoming the main barriers for the wide spread application of diamond film.Dynamic friction polishing is a new polishing technique which can realize fast polish by the complex friction-thermochemistry effect in processing area. It enables the processing area to achieve the transition temperature (usually 600～750℃) for graphitization of diamond in atmosphere by the high-speed friction effect between polishing plate and diamond, and then non-diamond carbon will be removed by mechanical, oxidation or diffusion effects to plate during polishing process.This polishing technique is very promising because it neither requires vacuum or sealed atmosphere nor needs heating equipment. Therefore, the key of dynamic friction polishing technique is urgent to develop a new type of polishing plate material with the high quality and strong catalytic graphitization ability on diamond. Although the Fe based alloy, Ni based alloy and Mn based alloy have catalytic graphitization ability on diamond, they exist poor wear resistance, low processing efficiency and poor high temperature oxidation resistance.A new type of polishing plate material-WMoCr alloy, was developed by the technology of mechanical alloying and hot-pressing sintering, aiming at solving the existing problems mentioned above of in dynamic friction polishing techniques. Then the performance of polishing plate and mechanism of diamond removal were analyzed. The main research contents include:(1) The effects of mechanical alloying parameters on powder properties were studied, and the results showed that the optimal mechanical alloying process was obtained: ball-to-powder, milling time, milling speed, liquid-to-ball and powder ratio are 15:1,45h, 250r/min,1:1 respectively. The prepared composite powders had fine grain, uniform distribution and excellent mechanical properties, which can enhance the oxidation resistance and the wear resistance of alloy.(2) The different contents of W and Mo affect the properties of polishing plate, so W72Mo27Cr1, W60Mo39Crl and W30Mo6Cr1 polishing plates were designed. The performance of polishing plate and dynamic frictional polishing process were analyzed. The results showed that W72Mo27Crl polishing plate had better comprehensive performance, and its hardness was 855HV, the material the removal rate of diamond was 5.44μm/min and the wear rate of polishing plate was 0.12 mm3/min.(3) The process of dynamic friction polishing on diamond by WMoCr alloy is observed. Detecting the changes in chemical composition of diamond and plate before and after polishing, the material removal mechanism is investigated. It is found that diamond is removed by transformation of diamond to graphite and then removed by mechanical oxidation or diffusion into plate during polishing process.