Oxidation behavior resistance of a duplex NiAl/Ti-Ni-Al coating by microwave assisted SHS on Ti substrate

Microwaves have been used to ignite the Self-propagating-High-temperature Synthesis (SHS) of Ni and Al powder mixtures to produce a duplex intermetallic coating on Ti substrates. Due to the high exothermic nature of the reaction, the newly formed NiAl is in the liquid phase and can react with the underlying Ti to form a tough ternary intermediate layer in a one step process. The obtained thick intermediate layer, Ti-Ni-Al ternary compound, with improved mechanical properties could replace the functionality of hard and brittle NiAl aluminide coatings in service. Moreover, the thickness of the intermediate layer, presenting an interlocking microstructure, can be controllably altered, up to 500μm, by annealing at 950°C for times ranging in the 3-20 minutes. The present work intends to assess the high temperature performances of the Ti-Ni-Al ternary coating, compared to pure Ti, Ti-6Al-4V and NiAl. In particular, cyclic oxidation response in the 750-900°C range and wear resistance at 750°C, measured using a ball-on-disk tribometer, were evaluated. The tendency for scale spallation, adherence and oxidation rates for NiAl and Ni-Al-Ti intermediate layer was evaluated as well.