Heat transfer mechanisms and their effects on microstructure during spray atomization and codeposition of metal matrix composites

Abstract

In the present study, the thermal mechanisms affecting the evolution of microstructure during spray atomization and codeposition of metal matrix composites were investigated, with particular emphasis on the effect of the ceramic phase on the resulting microstructure. The present results suggest that the grain size refinement that is commonly observed when a distribution of ceramic particulates is coinjected into a metallic spray during spray atomization and deposition processin may be rationalized by considering heat transfer effects and solid state cooling effects. In order to provide insight into the heat transfer effects, a heat transfer model was formulated on the basis fundamental heat transfer considerations. In this model, the transfer of thermal energy from the atomized metal to the ceramic phase was computed for two separate stages: (a) atomization and (b) deposition. The numerical results obtained using SiC particulates in an aluminum matrix show that 9% of the nethalpy of the atomized spray is transferred to the ceramic particulates during atomization, whereas 8% of the thermal energy available after deposition will be consumed in the process of equilibrating the temperature of the SiC particulates to that the matrix. Regarding solid state cooling effects, preliminary results suggest that the presence of a dispersion of ceramic particulates in the aluminum matrix will drastically reduce the rate of grain growth. This observation was corroborated through an experimental investigation of the changes in grain size after isochronal thermal anneals.