In Situ High Temperature X-Ray Diffraction Reveals Residual Stress Depth-Profiles in Blasted TiN Hard Coatings

High temperature X-ray diffraction (XRD) is used to characterize residual stress depth-profiles and volume-averaged residual stresses in blasted 9 Am thick TiN coatings on WC/Co substrates in the temperature range of 25-1100 degrees C using a dedicated high temperature attachment from Anton Paar GmbH. Room temperature measurements reveal that the blasting process changes the almost constant tensile residual stress of 560 MPa across the coating to compressive stress which decreases exponentially within the coating surface region of 1-3 mu m. The magnitude of the compressive stresses is dependent on the particle pressure used during the blasting process. Heating up results in rapid compressive stress relaxation already at relatively low temperatures and is accompanied by relaxation of stresses of II and III order. During cooling down from 1100 degrees C, tensile residual stresses are formed. After reaching the original stress value of about 560 MPa, the tensile stresses do not increase upon cooling anymore but are relaxed by cracks. The analysis of diffraction peaks shows that blasting results in anisotropic nano-structural changes in the coating surface. In summary, the approach documents that HT-XRD can provide important insights into the high temperature behavior of engineering components.