High velocity oxy-fuel coating technique: evaluation of residual stresses

The high velocity oxy-fuel thermal spray coating technique is investigated with regard to the residual stresses which can grow in the coating and in the coated material. The hole-drilling strain-gauge method is used to measure the stresses. Different preheating temperatures of the specimen surface and the influence of the thickness coating are tested. Statistical analyses exclude the influence of the interaction of these variables. While the preheating temperature has a dramatic effect on the measured strain, the effect of the variation of the thickness of the coating is secondary. The residual stress evaluated at the set of most favourable conditions show that the tensile residual stress are of the same magnitude of the yield stress of the material. There is no evidence of coating-substrate interface singularity.