SPRAY FORMING OF AL SIC METAL-MATRIX COMPOSITES/

This paper describes the as-sprayed microstructure of a model Al-4wt%C u/SiC particulate (Al4Cu/SiCp) metal matrix composite (MMC) manufactur ed by spray forming, and the relationship between microstructure and s olidification conditions during manufacture. Injection of SiCp, into t he melt atomization region during the spray forming of A14Cu results i n significant SiCp incorporation into molten droplets during atomizati on, and relatively little incorporation during flight to the substrate and at deposition. SiCp clustering is evident; in the A14Cu droplets and results in clustering in the as-sprayed MMC deposit. Matrix disloc ation and precipitation microstructures are dependent upon local solid ification conditions during spray forming, Increased dislocation densi ty and increased quantity of fine-scale theta'-Al2Cu precipitation is found in the alpha-Al(Cu) matrix where local deposit cooling rates are high, i.e. in the vicinity of the substrate/deposit interface and whe n increased spray distances are used in manufacture. Lower dislocation density and increased quantity of grain-boundary theta-Al2Cu is found where deposit cooling rates are relatively low, i.e. distant from the substrate/ deposit interface and at decreased spray distances. In all cases, dislocation densities are higher in alpha-Al(Cu)/SiCp, interfa cial regions than in the alpha-Al(Cu) matrix. There is no evidence of alpha-Al(Cu)/SiCp interfacial reaction in the as-sprayed condition ind icating that cooling rates during spray forming are sufficiently rapid to prevent reaction.