Thermal spray processing of ethylene methacrylic acid and polymer-ceramic composites

Thermal spray coatings are comprised of millions of heated particles driven at high velocities onto a substrate; thereby building up and forming a consolidated coating. Thus, investigating single solidified droplets contributes to the fundamental understanding of the evolution of a surface coating and its properties. A single splat is the building block of a thermal spray coating; thus, investigating single splats is essential to understanding thermal spray coatings and their properties. In this study, the spreading behaviour and the morphology of flame sprayed ethylene methacrylic acid (EMAA) splats, deposited at various stand-off distances (SODs) onto glass and mild steel substrates were investigated. A splat shape transition from a “splash” to a “disc shape” was observed. The morphology of EMAA droplets exhibited splashing when sprayed onto the mild steel substrates at room temperature, whereas a more regular uniform disk was formed when deposited onto glass substrates. It is suggested that more rapid freezing occurs on mild steel than on glass substrates due to the higher thermal conductivity of steel. Gas release from the substrate, due to input heat from the particle at impact, is another mechanism that gives rise to splashing. This work analyses splat morphology, developed from experiments, and classifies the taxonomy of single splats of EMAA. The surface chemistry of the substrates plays an important role in splat morphology. The volatiles of condensates cause bubbles in the splats, generate splashed splats and fragmented splats. Heat treatment at 100 °C influences the chemistry of the mild steel surface. The X-ray Photoelectron Spectroscopy (XPS) experiments indicate that the adsorbed H2O disappears from the surface of the mild steel sample after one hour of heat treatment at 100 °C. There is no adsorbed water on the surface of the unheated glass sample. Preheating conditions affect splat morphology. The statistical study of the SOD effect on the metrology of splats shows that the target efficiency of EMAA decreased dramatically with increases in the SOD. Increasing SOD resulted in more spherical splats.