Dry-Blasting of α- and κ-Al_2O_3 CVD Hard Coatings: Friction Behaviour and Thermal Stress Relaxation

摘要

Post-deposition blasting treatments of cemented carbide cutting tools coated by chemical vapour deposition have gained increasing interest. Within the present work, α- and κ-Al_2O_3 coatings dry-blasted using different pressures as well as globular and edged blasting materials were investigated. A higher pressure resulted in an increase in the compressive residual stresses, as determined by X-ray diffraction. Both blasting materials had a minor influence on the roughness of α-Al_2O_3, while the edged material caused a significant roughness increase for κ-Al_2O_3. For α-Al_2O_3 dry-blasted using the globular material, complete stress relaxation could be observed after annealing at 500℃, whereas for α-Al_2O_3 dry-blasted using the edged material as well as for the κ-Al_2O_3, an annealing temperature of 900℃ was necessary for stress relaxation. The friction coefficient of the dry-blasted samples first increases with increasing temperature, due to increasing plastic deformation of the blasting material transferred onto the coating surface, until it decreases again above 700℃, due to softening of the transferred material.