Conditions and mechanisms for the bonding of a molten ceramic droplet to a substrate after high-speed impact

Abstract In this study, the mechanism controlling the formation of a chemical bonding between a ceramic melt and a solid body prior to the melt solidification was investigated using the thermal spraying process as an example. The formation of a chemical bonding between TiO2, LCO, LZO, YSZ splats and ceramic substrates of the same material was investigated focusing on the effect of the deposition temperature. The bonding state was examined by studying both fractured cross-section samples and samples prepared utilizing the focused ion beam (FIB) technique. The microstructure at the interface of typical FIB-prepared cross section samples was examined by high-resolution transmission electron microscopy. The results show that an effective bonding at the splat interface can be formed only when the deposition temperature is higher than a critical bonding temperature. The critical bonding temperature linearly increases with the melting point of the ceramic material. The interface temperature, directly influencing the bonding formation, was calculated utilizing a one-dimensional heat transfer model. The maximum interface temperature corresponding to the critical bonding temperature was found to be close to the glass transition temperature of the splat material. Thus, the concept of an intrinsic bonding temperature and a sufficient condition for the formation of an efficient bonding are proposed. Furthermore, a model for the bonding mechanism at the melt/solid interface is established to explain the bonding formation and the microstructure at the interface.