Flattening of droplets and formation of splats in thermal spraying: A review of recent work - Part 1

Properties of the coatings developed during thermal spraying are essentiall y determined by rapid solidification of splats formed as a result of imping ement of the melted powder particles onto a substrate surface, The processe s of flattening droplets and formation of splats in thermal spraying have b een studied intensively during the last two decades, The last review on thi s topic was published at the end of 1994, Since then many papers have been dedicated to investigating splat formation, taking into account such import ant issues as roughness of the substrate surface, wetting phenomena, and sp lashing. This review, consisting of two parts, includes the main results ob tained since 1994 and examines the influence of solidification of the lower part of the splat, substrate roughness, wetting at the substrate-coating i nterface, substrate deformation, oxidation, and splashing on the dynamics o f flattening of droplets and the formation of splats. Flattening of composi te powder particles, splat-substrate interaction, and development of splat- substrate adhesion and splat porosity are discussed. Part 1 of the review c overs the following issues, which significantly influence the droplet flatt ening and splat formation: droplet solidification during flattening and rou ghness of the substrate surface, composite morphology of the powder particl es, and oxidation processes, The results provide a better understanding of the thermal spray processes to increase their efficiency.