In Situ Monitoring of Particle State and Deposition Rate Effects on Coating Formation

When optimizing process parameters, diagnostic systems play a key role enabling the control of particle state by flame tuning. Other parameters such as deposition rates (raster speed and feed rate), spray distance, deposition temperature, can be complementarily investigated by analyzing the stress buildup in real time during deposition. Particle state, micro- and macro-cracking, peening intensity, yielding, cohesion are among others, variables that influence the residual stress state in the deposited layers. Therefore, they enable information of the evolution of the microstructure during spraying while modifying process parameters. In this study, the development of stress during deposition is discussed in regard to the particle state and deposition conditions versus microstructure and properties for several materials systems: YSZ, TiO₂ – by APS; and Al₂O₃, WC-Co, NiCr – by HVOF. Particle state was varied accordingly to a DoE framework of first order process maps. Deposition conditions such as relative speed, spray distance, substrate temperature, and feed rate were varied to study their effect on coating formation.