Particle in-flight behavior and its influence on the microstructure and mechanical properties of plasma-sprayed Al2O3 coatings

This paper aims to elaborate the particle characteristics during their flight into the spray and its significance in determining the microstructure and mechanical properties of resultant coatings. Study of plasma spraying of Al2O3 using three different grain fractions of feedstock was done by an on-line monitoring system (SprayWatch 2i). The as-sprayed coatings were characterized in terms of the microstructure and composition, microhardness, adhesion strength and porosity. In addition, a statistic study of Weibull analysis was employed to further examine the microstructural homogeneity of coatings. It was found that particle in-flight behaviors are strongly influenced by feedstock particle size. Improved particle velocity and temperature as well as melting extent can be obtained for the finer feedstock. This contributes to produce increasingly bonded splats resulting in coating with compact microstructure, where low porosity and increased microhardness and adhesion strength were realized.