Formation of metal matrix composite reinforced with Nano sized Al2O3 + Ni―Al intermetallics during coating of Al substrate via combustion synthesis

A hard composite coating was synthesised on an Al1100 alloy substrate, using combustion synthesis reactions. A thin cylindrical compact of an exothermic pre-milled reactive powder mixture of Ni + 14Al + CuO + 2NiO was used. The compact was placed on the substrate and was heated up to the ignition temperature of the reactants, under static pressure. The cross section of the coated substrate was investigated using XRD and SEM with EDS. The coating and the substrate Vickers microhardness profiles were obtained. The coating layer comprised multi-phases including Al2O3 nanoparticles and different Al, Ni and Cu intermetallic compounds. A fusion layer from the bonding interface into Al1100 substrate was observed which was due to the released heat from the combustion synthesis reactions. This caused the diffusion of nickel into the substrate and a strong bonding so that no micro void or microcrack was observed at the interface even at high magnifications. The mean thickness and hardness of the obtained coating layer were 400 micron and 80 VHN, respectively.