THERMAL BEHAVIORS OF DROPLET–SUBSTRATE IN THEHRMAL SPRAY NEW APPLICATIONS

There have been efforts to expand the thermal spraying capabilities for deposition of inexpensive electronic and magnetic materials for electronics, medical, sensor and fuel cell applications, such as metal bipolar plates produced for proton exchange membrane (PEM). For electronic materials deposited by plasma spray method the presence of porosity, splat boundaries, and microstructures formed during rapid solidification, would contribute additional blocking interfaces not found in traditional polycrystalline silicon systems deposited by CVD, PVD, or casting methods. Therefore understanding and controlling of these thin film formation by thermal spray are of interest. Recently, substrate heated by plasma gun or by external laser beam has been proposed to enhance the mechanical and thermal properties of the electronic and magnetic depositions. Studies were found that substrate may be melted with substrate heating. It can help to improve the bonding and stress distribution inside. When droplets solidified on a thin liquid layer at the top of the substrate, conditions will be similar to crystal growth and epitaxy film will be achieved. It is therefore possible to use substrate melting as tool to promote epi-layer growth by plasma spraying. Difficulty is how to control the substrate temperature during droplet solidification and satisfy the growth conditions. In this study we will propose a design for temperature control to control the substrate melting and epitaxy growth based on the analysis of the droplet-substrate thermal behaviors. If directional solidification of the splats can be achieved and controlled, as well as good adhesion from substrate melting, thermal spraying may find many new applications. It is possible to extend the traditional thermal spray technology into meso-scale electronics.