INFLUENCE OF Ti COATING ON MECHANICAL PROPERTIES OF DIAMOND GRITS

Abstract In this paper, diamond is coated with Ti by vacuum slowly vapor deposition process. The effect of Ti coating on diamond strength and the correlation between impact property and wear stages of grits are investigated with static and dynamic processes, Scanning Electron Microscope (SEM) and Stereo Microscope. The influence of Ti coating on wear stages of diamond grits in actual tool is studied as well. This research provides some theoretic and practical bases for selection of diamond and improvement of tool抯 efficiency and lifetime. The results indicate that compressive fracture strength (CF 5) of Ti-coated diamond is improved due to surface strengthen effect. For different diamond, the increase percentage of CFS is different, at most it reaches 27.5%. However, toughness index (TI) of diamond has little changes before and after coating with Ti, because it is more dependent on diamond internal composition and defects than CFS. Diamond grits after impacting are first divided into three categories with screening process: un-broken, micro-fracture and completely fracture, which is respectively corresponding to no significant wear, micro-fracture and macro-fracture in segmented diamond tool. Thus the correlation between the fracture of impacted grits and the wear stages of grits in actual diamond tool is established. Test results show that the optimum working condition of every diamond exits, and only when the ratio of un-broken grits and micro-fracture ones is close to 1:1 under certain working condition that this is the optimum state of force operating on grits. Under this condition, cutting efficiency and self-sharpness of the diamond tool achieve best, so that its lifetime and efficiency are improved obviously. Compared with that of un-coated diamond, the percentage of every wear stage of Ti-coated diamond in practical tool changes. The percentage of pull-out is greatly reduced from 55% to about 10%, while no significant wear and micro-fracture grits participating in effective cut are both increased, which increases tool抯 lifetime and efficiency.