Influence of spraying conditions on microstructures of Al-SiCp composites by plasma spraying

Air plasma spraying was used to produce Al-SiCp composites as electronic packaging material. Ball-milled Al with 55 and 75 vol. pet SiC powders was repeatedly deposited onto a graphite substrate, and then mechanically removed to get free-standing 100 X 100 mm composite plates of about 2-mm thickness. Different input electrical powers were employed at two spray distances of 100 and 120 turn. The SiC volume fraction and porosity in the sprayed composites were found to be dependent on spray conditions, especially input electrical power. Maximal SiC volume fraction can be obtained at a low input electrical power for the composite sprayed from the Al-55SiC powder and a high input electrical power for Al-75SiC powder. The variation of the SiC level in the composites with spray conditions and SiC size is discussed based on the characteristic of feedstock, the characteristic of deposited surface, and the heat and momentum transfer between particle and plasma flame. Pores in the sprayed composites were found inside one sprayed layer (inner-layer pore) and at the boundary between two sprayed layers (interlayer pore). The formation mechanisms of two types of pores are also explained. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses indicate that Si phase is formed in the sprayed composites for most spray conditions. The Si resulted from the decomposition of SiC particles in high-temperature plasma flame.