Evaluation of through thickness residual stresses in thermal sprayed WC–Co coatings

Abstract

Evaluation of residual stress in WC–Co coatings has intrinsic limitations such as high hardness and low penetration of X-ray into WC. In this study the through thickness residual stress of WC-12Co coatings in high velocity oxy fuel (HVOF) thermal spraying using liquefied petroleum gas (LPG) was studied by means of electro discharge hole drilling. Therefore, because of noncontact nature of electro discharge hole drilling as an electro-physical process it is possible to drill the WC–Co coatings independent of hardness. Additionally, the sin2 ψ method after layer removal process was used by means of X-ray diffraction (XRD). The results confirmed the feasibility of the residual stress measurement by electro discharge hole drilling for WC–Co coatings. Scanning electron microscopy, X-ray diffraction, Electro discharge hole drilling (EDHD) and Spray Watch diagnostic system were applied. The average of in-depth residual stress in coating sprayed with the highest velocity using hole drilling and XRD methods was −50.88 and −40.52 MPa, respectively.