Synthesis and fabrication of NiAl coatings with Ti underlayer using induction heating

The objective of this work was to develop a new technique to synthesize and fabricate NiAl coatings on a steel substrate in one processing step. Induction heating was used as the ignition source to initiate the self-propagation high-temperature synthesis (SHS) reaction of Ni/Al, while titanium was used as the underlayer to facilitate the adhesion between the coating and the substrate. The temperature profiles during the process were measured to monitor the heating and synthesis reaction in the coating and underlayer. The microstructure and the phase compositions of the synthesized products were studied using SEM and XRD. The results showed that the SHS reactions of Ni/Al produced stoichiometric and substoichiometric NiAl such as Ni0.58Al0.42 and Ni1.04Al0.96 in the coating. The Ti underlayer joined the reaction. The reacted part changed into Ti3Al-Ti2Ni composite and the unreacted Ti formed an alloy with the NiAl. The mechanical properties of the synthesized products, evaluated using Vickers indentation, showed that the hardness of the underlayer was higher than that of the coatings and substrate, while the test at the substrate/underlayer interface indicated that the existence of a Ti underlayer had improved the adhesion between the coating and the substrate.