Spallation of a substrate by thermal shock and thermal expansion differential during splat cooling

The manufacture of metal-matrix composite materials by spray deposition is a very attractive process, but impaired by the spallation that may take place after impact of molten metal droplets on the fibers. In this work, the spallation of a quartz substrate was investigated through video and acoustic measurements and through temperature measurements of the splat surface. The time scales pertaining to the fracture mechanisms are examined from acoustic measurements of the spallation. The spall formation mechanism was quantified by analyzing the geometric configuration of the splats and spalls under varying conditions of droplet superheat, droplet size, and droplet or substrate material. Furthermore, the thermal contact resistance between the splat and the substrate was evaluated by matching the measured temperatures of the top or bottom surface of the splat with numerical results from a heat conduction model with phase change.