Substrate temperature effects on the splat formation, microstructure development and properties of plasma sprayed coatings

Abstract

The effects of substrate temperature on plasma sprayed molybdenum splat morphology, deposit microstructure development, and properties have been investigated. The molybdenum splat morphology changes from a fragmented (splashed) to a more contiguous disk shape with increasing substrate or deposit surface temperature. Furthermore, the flattening ratio of the splats prepared on glass is significantly higher than those prepared on steel or molybdenum substrates. With an increase in substrate temperature the deposit exhibits improved lamellar structure with less interlayer pores and fine particle debris (arising from splashing). The oxygen content in the deposit increases with substrate temperature associated with increased surface oxidation subsequent to deposition. The thermal conductivity, hardness and intesplat contact area are enhanced with increased substrate temperature. The fracture characteristics change gradually from interlamellar to translamellar, indicating enhanced interlamellar bonding among splats. The residual stress changes gradually from tensile to compressive with increasing temperature, its magnitude depending on the substrate materials and associated thermal mismatch stresses. A higher substrate temperature dramatically improves the adhesion and bonding of the splats and, therefore, enhances the physical and mechanical properties of the coatings.