Experimental measurements have been carried out with the aim of investigating the residual stresses generated during plasma spray deposition of glass composite coatings. The research shows that the behaviour of these materials is fundamentally different from metals and ceramics. The quench stress in the glass composites can be eliminated by plasma-scanning. This is attributed to their low glass transition temperatures, which enable the stresses to be completely relaxed. The work also shows that the addition of alumina as a second phase allows the expansion mismatch between the coating and the steel substrate to be controlled. Control of the second-phase volume-fraction enables the residual stress in the composite coatings to be reduced to zero. Real-time measurements on deflection and temperature show that the dimensions of the substrate, plasma operating conditions and scanning rate have substantial effects on the temperature profiles within the deposits. Keywords: glass composite coatings, thermal stress, plasma spraying.

A ball-milled mixture of glass and alumina powders has been plasma sprayed to produce alumina-glass composite coatings. The coatings have the unique advantage of a melted ceramic secondary phase parallel to the surface in an aligned platelet composite structure. The alumina raises the hardness from 300HV for pure glass coatings to 900HV for a 60wt% alumina-glass composite coating. The scratch resistance increases by a factor of three and the wear resistance by a factor of five. The glass wears by the formation and intersection of cracks. The alumina wears by fine abrasion and supports most of the sliding load. The wear resistance reached a plateau at 40-50vol% alumina, which corresponds to the changeover from a glass to a ceramic matrix. Keywords: glass composite coatings, wear, thermal spraying