Oxidation Behavior of Ti₅₀Ni₄₀Cu₁₀ Shape-Memory Alloy in 700–1,000 °C Air

摘要

The isothermal-oxidation behavior of Ti₅₀Ni₄₀Cu₁₀ shape memory alloy (SMA) in 700–1,000 °C air was investigated by TGA, XRD, SEM and EPMA. Experimental results indicate that a multi-layered oxide scale formed, consisting of an outermost Cu₂O(Ni,Ti) layer, a layer of the mixture of TiO₂, TiNiO₃ and irregular small pores, a layer of the mixture of Ni(Ti,Cu), TiO₂ and irregular large pores, a Ti(Ni,Cu)₃ layer and an innermost Ti₃₀Ni_43–47Cu_27–23 layer. The apparent activation energy for the oxidation reaction of Ti₅₀Ni₄₀Cu₁₀ SMA is determined to be 180 kJ/mol, and the oxidation rate follows a parabolic law. A schematic oxidation mechanism of Ti₅₀Ni₄₀Cu₁₀ SMA is proposed to explain the observed results. Keywords TiNiCu shape memory alloy - Oxidation mechanism - Oxidation kinetics