A study of Ni₃Al coating on carbon steel surface via the SHS casting route

A nickel aluminide (Ni₃Al) coating on a carbon steel surface was fabricated by the self-propagating high-temperature synthesis (SHS) casting route. Coating phases were determined by using X-ray diffraction (XRD). The microstructure of the coating and bonding interface between the substrate and the coating, and the distribution of elements adjacent to the interface, were analyzed by using electron probe microanalysis (EPMA). The microhardness of the coating was measured. The tribological properties of the coating at different elevated temperatures were investigated and the worn surfaces at different temperatures were analyzed by EPMA. The elemental chemical state of the worn surface was determined by using X-ray photoelectron spectroscopy (XPS). The results show that the coating was composed of Ni₃Al phase, and that its microstructure was dense and pure. Elements had diffused mutually at both sides of the interface and a metallurgical bonding interface was formed. The heat of the reaction coarsened the grain size of the substrate near the interface. The hardness of the coating is higher than that of the substrate. Wear loss and friction coefficient of the coating vary with the testing temperature. The coating had a good resistance to oxidation at elevated temperature. Oxidation of the coating occurred as a result of friction at the temperature of 873 K. The mechanisms of combustion synthesis of Ni₃Al coatings on carbon steel substrates are discussed in detail. It is pointed out that the combustion temperature and the wettability between the product of the reaction and the substrate are significant to obtain the coating.