Effect of electroless coating parameters and ceramic particle size on fabrication of a uniform Ni-P coating on SiC particles

The formation of a uniform nickel phosphorous (Ni-P) electroless (EL) coating on micron-sized SiC particles was investigated in this study. Metal coated ceramic particles could be used in applications including as the fabrication of cast metal matrix composites.Such ceramic particles have a better wettability in molten metal. In this work, the effects of EL coating parameters, SiC particle size and morphology on the coating uniformity and mechanical bonding at the SiC/Ni-P interface were studied. The results indicated that etching treatment was very effective (especially for coarse powders) on the mechanical bonding at the interface. Theoptimum values of bath temperature and pH were determined to be 50±2 °C and 8±0.2, respectively. The best uniformity and mechanical bonding were obtained for SiC particles with average particle size of 80 μm (considered relatively as coarse powders in this study). The ball milling of SiC particles (with the average particle size of 80 μm) for 1 h led to the formation of a multi-modal particle size distribution which resulted in a non-uniform quality of particulate coating. The larger SiC particles after ball milling were more completely covered by the Ni-P coating compared to the smaller more fragmented particles. The smaller ceramic particles processed via Ni-P EL coating lead to formation of segregated clusters of Ni-P and therefore such ceramic particles contained many uncoated parts.