Microstructural characterization of small-particle plasma spray coatings

The microstructure of a small-particle plasma spray (SPPS) aluminum oxide c oating sprayed onto a prepared mild steel substrate has been characterized using a variety of microscopic techniques as part of a process optimization study. The coating was highly conforming to the substrate as evidenced in high-resolution transmission electron microscopy, although some voids were present at the interface. The layered splat microstructure, characteristic of conventional plasma-sprayed coatings but smaller in size, was discerned in partially thinned samples in a focused-ion-beam scanning electron micros cope (FIB-SEM), Microcracks and microporosity, generally less than 0.5 mu m in size, was also seen between splats using transmission electron microsco py, Cubic alumina of the crystallographic form gamma-Al2O3 was identified b y electron diffraction.