THE EFFECT OF CERAMIC REINFORCEMENTS DURING SPRAY ATOMIZATION AND CODEPOSITION OF METAL MATRIX COMPOSITES .2. SOLID-STATE COOLING EFFECTS

In the present study, the mechanisms governing the evolution of microstructure during spray atomization and codeposition of metal matrix composites (MMCs) were investigated, with particular emphasis on the effects of the ceramic phase on the resulting microstructure during solid-state cooling. 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 processing was rationalized in terms of three distinct effects: (a) solidification effects, (b) heat-transfer effects, and (c) solid-state cooling effects. The solidification and heat-transfer effects were discussed in Part I.[1] Regarding solid-state cooling effects, the present results show that the presence of a dispersion of ceramic particulates in the aluminum matrix effectively reduces the rate of grain growth during solid-state cooling. Experimental support to this suggestion was provided by the results of an investigation on the changes in grain size following isochronal thermal anneals.