Evaluation of residual stress in HVOF stellite-6 coatings using non-contact drilling
Institute of Physics
School of Engineering
Because of high hardness of stellite coatings it is impossible to evaluate the residual stress through the thickness using standard methods such as hole drilling (ASTME837). Applying a drilling method with hardness independent nature is necessary to find the stress state from the surface toward coat-substrate interface. In this study the residual stress profile of stellite-6 overlaid on steel substrate has been studied using electro-discharge milling. To have an exact evaluation on residual stress, the elasticity modulus of coating was measured applying Knoop indentation. Scanning electron microscopy and XRD were used to study the microstructure, morphology phase composition of powder and coating. The maximum compressive and average value of residual stress from surface to the coat-substrate interface obtained of −198 MPa and −108 MPa respectively. The explicit and implicit finite element was used in order to develop a model for simulation of the peening and cooling stresses respectively. The implicit result for coating sprayed in 740 m s−1 indicates the presence stresses of +170 MPa and −270 MPa at the surface and interface respectively with average of −93 MPa thorough the thickness which show good agreement between the experimental and numerical results.