Ultrafine grain diamond thin films were deposited on the WC-Co-based drills by electron-aided hot filament chemical vapor
deposition (EACVD). Considering the fact that the drill is of very complex geometrical characteristics, which brings much difficulties to its pretreatment process, a new multiple chemical pretreatment technology including microwave oxidation, reaction in alkaline solution and cleaning by ultrasonic treatment in acid solution was developed. The effects on the diamond adhesion strength, nucleation and surface morphology were investigated. At the same time, a special EACVD process called varied parameters controlling model was developed. By this new model,
ultrafine grain diamond film can overlap on the previously deposited diamond film consisted of large facet grains. The high quality diamond-coated drills with good adhesive strength and smooth roughness can be obtained. The cutting performances of the diamond-coated drills were investigated by drilling SiC particles reinforced aluminum matrix composites. The significant wear resistance and good chip evacuation capability lead to the reduced torque and thrust force, which improves the cutting performance of this kind of drill.