Oxidation behavior of equiatomic TiNi alloy in high temperature air environment

The isothermal oxidation behavior of equiatomic TiNi shape memory alloy in dry air from 550 to 1000 degrees C is studied with thermogravimetric analysis. The alloy's scale layer is further investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalyzer. Experimental results indicate that a multi-layered scale is formed, consisting of an outer rutile layer, a porous intermediate layer of mixture of TiO2 and Ni(Ti), and a thin inner TiNi3 layer. The intermediate layer, furthermore, exhibits a stripe-like lamellar structure at the TiNi3 interface. The apparent activation energy of TiNi alloy oxidation is 226 kJ/mol, and the oxidation rate follows a parabolic law. A schematic oxidation mechanism of TiNi alloy is proposed to explain the observed results.