Ni-Al-Ti coatings obtained by microwave assisted SHS: Oxidation behaviour in the 750-900 °C range

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, belonging to the Ti-Ni-Al system, in a one step process. Aim of this work is to assess the high-temperature performances of the Ti-Ni-Al layer, compared to NiAl coating and Ti. Experimental results demonstrate that the ternary layer presents oxidation resistance comparable to NiAl up to 750 degrees C. In this condition, the thick Ti-Ni-Al layer could replace the functionality of hard and brittle NiAl coatings. At 900 degrees C, instead, NiAl oxidation resistance results higher, and this can be ascribed to the relatively low Al content in the studied ternary compound, which hinders the formation of a continuous and protective scale. (C) 2009 Elsevier B.V. All rights reserved.