JTTEE 3:216-218 9 International Transport Phenomena in Spray Processing of Structural Materials: An Extended Abstract* Y. Wu and E.J. Lavernia The interaction behavior between metallic droplets and ceramic particulates during spray atomization and co-injection is investigated in the present investigation. A model is developed to predict the penetra- tion of ceramic particulates into metallic droplets in the liquid and semi-liquid states. Both surface ten- sion and fluid drag forces are considered in formulating the penetration behavior of ceramic particulates. It is found that the penetration ability of ceramic particulates increases in the sequence: graphite, SiC, A!203, and TiB2. 1. Introduction AN important aspect of discontinuously reinforced metal matrix composite (MMC) fabrication is the incorporation of ceramic reinforcements into metallic matrices. In particular, in the liquid and semisoFid processing of particulate-reinforced MMCs, it is often necessary to incorporate ceramic particulates into the ma- trix materials through stir mixing, centrifugal mixing, or gas in- jection (Ref 1-5). Spray atomization and codeposition processes, for example, involve the co-injection of ceramic particulates into a dispersion of matrix droplets under highly nonequilibrium thermal and so- lidification conditions (Ref 5-7). An example of the interactions that occur between ceramic particulates and alloy droplets dur- ing spray atomization and codeposition is shown in Fig. 1. In the processes of spray atomization and co-injection, each particular droplet may be in the liquid, semiliquid, or solid state, depend- ing on factors such as droplet size and solidification kinetics. During the impact with such droplets, ceramic particulates may break through the surface and penetrate the droplets if they pos- sess sufficient kinetic energy. The complex factors that affect penetration behavior render the prediction of penetration a challenging task. Although ex- perimental evidence has shown that ceramic particulates may penetrate metallic droplets during co-injection, there is still a need for a systematic study of the penetration phenomenon. composite powders were synthesized using a spray atomization and co-injection approach. The penetration of ceramic particu- Atomized / ~ ~ \ Atomization droplet ~ O O \ cone Particulate / ~ 0 0 Particulate injection t~ I~ ~,~\injection Particu ~4"kal O O ~o~nposite 9 | / &gJ ~ ,'& ,', ' 0 Fig. 1 Schematic diagram showing the interactions between ceramic particulates and metallic droplets during spray atomization and co-in- jection 2. Interactions between Droplets and Reinforcements The present investigation examines the penetration behavior of ceramic particulates into metallic droplets during spray at- omization and co-deposition. To that effect, A1-4wt%Si-SiC, Al-12wt%Si-SiC, A1-4wt%Si-TiB2, and aluminum-graphite Key Words: deposition, interactions, SiC metal-matrix particulates composites, penetratingspray Y. Wu and E.J. Lavernia, Materials Scienceand Engineering, Depart- ment of Mechanical and Aerospace Engineering, University of Cali- fornia, Irvine, CA 92717 *Extracted from the Symposium on Spray Forming, paper l of 12 con- tributions, National Thermal Spray Conference, Anaheim, June 1993. This abstracthas been edited by C.C. Berndt (SUNY at Stony Brook). (a) (b) Fig. 2 The presence of ceramic particulates in aluminum-silicon powders preparedby spray atomization and co-injection. (a) SiC. (b) TiB 2 216---Volume 3(2) June 1994 Journal of Thermal Spray Technology