Feasibility Study of an Adaptive-Pressure Plasma Coating Process-Part 1: Model Description

摘要

Thermal barrier coatings for gas turbine engines are mainly produced by electron beam physical vapor deposition or atmospheric plasma spray depending on the thermomechanical loading of engine components. This study deals with the numerical design of a two-step thermal plasma-aided physical vapor deposition process capable of efficiently evaporating the coating material processed in the plasma jet and of producing a strain-tolerant coating microstructure from vapor phase condensation. The system involved a high-pressure chamber and a low-pressure chamber connected by an expansion nozzle. The objective was to achieve the highest deposition efficiency for a given plasma specific enthalpy. The numerical simulations based on computational fluid dynamics and direct simulation Monte Carlo models projected the effect of the process geometry and operating conditions on the gas flow fields, powder vaporization efficiency and nucleation/growth phenomena in the gas phase. For a targeted powder feed rate, they allowed to determine the length of the high-pressure chamber, the diameter of the expansion nozzle and other dimensions of the deposition system. The expansion nozzle that linked the two chambers was the crucial component of the process, and the predictions made it possible to select the geometry and process operating parameters that avoided its clogging and/or melting.