Effect of doping level on residual stress, coating-substrate adhesion and wear resistance of boron-doped diamond coated tools

Abstract

Boron doping can change the basic properties of diamond coatings prepared by the hot filament chemical vapor deposition (HFCVD) method, including residual stress, coating-substrate adhesion and wear resistance. However, the specific effect of boron doping level on the properties of diamond coatings and the mechanism needs further investigation. In the present study, the tungsten cemented carbide (WC-Co) material is selected as the substrate to deposit boron-doped diamond coatings with different doping levels ranging from 0 to 15,000 ppm. To elaborate the influences of doping level on the boron-doped diamond (BDD) coatings, microstructure, surface roughness, grain orientation, nanohardness, Raman spectral, Kernel Average Misorientation (KAM) and Rockwell indentation of diamond coatings are characterized, then friction tests and milling experiments are conducted on all specimens. The results indicate that the appropriate doping level of 8000 ppm can change the grain orientation to (110) orientation, guarantee diamond quality and hardness, reduce the residual stress, minimize the coefficients of friction (COF) and improve the tool life. Raman and KAM analysis demonstrate that the specimen generates suitable tensile stress in the diamond lattice and offsets the compressive stress of the coating to obtain the lowest residual stress and the highest coating-substrate adhesion strength. Friction test results illustrate that the specimen has the best wear resistance because the grain with (110) orientation has high hardness and low COF. In addition, milling experiments illustrate that the specimen has the best machining life due to the combination of good coating-substrate adhesion and wear resistance, with a tool life of 355 min, which is 29.6 % longer than the machining life of the undoped diamond coated tool.