Effect of heat transfer on residual stresses in thermal spray coatings

Herein, heat transfer from the coating to the substrate during the thermal spraying process is simplified as one-dimensional heat conduction and a formula to express the temperature distribution in the substrate is provided. To achieve this, the spray process was divided into two stages, namely deposition (coating sprayed onto the substrate) and post-deposition (cooling of coating and substrate to atmospheric temperature). The coating was achieved through a layer-by-layer deposition method. Residual stresses in the system (including both the coating and substrate) following deposition of each layer were calculated, as well as those induced by post-deposition. Finally, the proposed formulae were implemented in a real-case example to illustrate the effect of heat transfer with regards to torch velocity on residual stresses. The simulative results were shown to have a better agreement with experimental results at low rather than at high torch velocities. The residual stresses in the coating surface decreased with the increase in heat transfer time. When the heat transfer time exceeded a certain value, a sharp decline in residual stresses was observed.