Heat flux investigations during flame thermal spray process using the lumped capacitance method

The evaluation of heat flux is vital in the field of thermal spray process since it decides the temperature gradient, the formation of the residual stress inside the coating and finally affects the coating properties. Especially for the specific net incident heat flux density launched by the torch during each passage, it affects greatly the interaction between the previous and latter adjacent layers, the temperature gradient formation as well as the residual stress distribution along the vertical direction during the coating deposition process. This work mainly concentrates on the estimation of heat flux density during flame thermal spray process based on a lumped capacitance model. The heat flux evolution during one multi-pass of the torch was analyzed in detail and the average heat flux density impinging the substrate surface was firstly estimated, the root mean square error between the measured temperature and the numerical estimation was selected as the evaluation criteria to compare the calculation accuracy. The dynamic increase of coating mass was then added into consideration and the net incident heat flux density launched by the torch was estimated. The peak power value of the heat flux density was estimated based on an assumed Gaussian form of thermal energy distribution.