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 synthesized upon an Aluminum1100 alloy substrate, using combustion synthesis reactions. A thin cylindrical compact of an exothermic pre-milled reactive powder mixture of “Ni + 14Al + CuO + 2NiO” was utilized for this purpose. This compact was placed on the substrate and they were heated up to the ignition temperature of the reactants, under static pressure. The cross section of the coated substrate was investigated using X-ray diffraction experiments and a scanning electron microscope (SEM) which was equipped with energy dispersive spectrometer (EDS). The coating and the substrate Vickers microhardness profiles were obtained. Results revealed that the coating layer comprised multi-phases including Al2O3 Nano particles 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 and caused the diffusion of Nickel into the substrate as well as a strong bonding so that no micro void or micro crack was observed at the interface even at high magnifications. The mean thickness and hardness of the obtained coating layer were 400 μm and 80 VHN, respectively.