Deposition of a molten layer of high melting point material: Substrate melting and resolidification

High melting point metals and their alloys have wide use as coating materials because of their improved properties. A good understanding of the bonding mechanism between the coating layer and the substrate is therefore a very important concern in thermal spray processing of these high melting point materials. In this work we have conducted a numerical study of the cooling and solidification of such materials, and in particular of the substrate melting and resolidification for a substrate impacted by a high melting point droplet. A model has been developed and a non-dimensional analysis led to the identification of the independent non-dimensional parameters controlling the process. Numerical solutions of this complex coupled problem enabled us to calculate the temperature history in both deposit and substrate, including the phase change phenomena. The critical conditions needed for substrate melting in the case of given pairs of deposit and substrate materials were quantified from systematic deposit and substrate temperature analyses, and are presented in terms of non-dimensional operational maps of wide applicability. Information on the critical conditions under which the substrate surface melts, and on the maximum melting depth achieved into the substrate was also generated for various process parameters including deposit undercooling, initial substrate temperature, and variations in deposit-substrate interfacial heat transfer coefficient.