Study of Thermal Constriction Phenomena for Drops Spreading Encountered During Plasma Spraying Processes

During a thermal spraying process, the heat flux reaches a few hundreds MW/m² while the spreading duration is extremely short, being about a microsecond. The interfacial phenomena of thermal deposit/substrate constriction play an extremely important role since they control the coating cooling rate, and as a consequence, the thermo-mechanical properties of the deposited layer. We present in this work an analytical solution intended for the computation of the thermal constriction resistance during the spreading. This solution is derived by using the Hankel finite transform and the Duhamel theorem leading to a simple expression as a series expansion with fast convergence. The effect of the spreading velocity on the thermal constriction resistance has been studied. Results show the existence of a critical threshold of spreading velocity for which the transient problem has to be considered. On the other hand (below the threshold) the steady state regime should be sufficient for the constriction estimate.