During thermal spray processes, metallurgical bonding between the impinging particle and the substrate surface due to substrate melting during droplet-substrate interaction can provide substantial contribution towards coating adhesion strength. Understanding of melting and resolidification of the substrate is thus essential for appropriate bond coat selection as well as avoidance of substrate damage. A numerical model has been developed to investigate the integrated effect of droplet solidification, and melting and re-solidification of the substrate during thermal spray. Various droplet and substrate pairs have been studied; the crater depth of the substrate has been measured and compared with the numerical prediction, and experimental results show that the material properties of both droplet and substrate play important roles on substrate melting. A dimensionless parameter, temperature factor, has been proposed and serves as an indicator for the potential of substrate melting. Based on the time scales of the droplet solidification and substrate melting and re-solidification, a substrate melting mechanism is proposed to explain the often-observed flower-like splat morphology. (C) 2004 Elsevier B.V. All rights reserved.