On the Corrosion Resistance of the Polycrystalline Fe–Mn–Al–Ni–Ta–B Superelastic Alloy in 3.5 wt% NaCl Solution

Abstract

The high addition of alloying elements in the Fe–Mn–Al–Ni (FMAN) alloy is discouraged as it may alter its thermoelastic martensitic transformation, introduce numerous precipitates that induce pitting or galvanic corrosion, and thus reduce its corrosion resistance. This study proposes an effective strategy to enhance the corrosion resistance of the FMAN alloy in a neutral solution without loss of superelasticity via Ta-doping. The slightly improved corrosion resistance in 3.5 wt% NaCl solution is attributed to the coupling effect of the Ta-rich austenite and Ta-rich precipitates with a low corrosion rate. In situ Raman results demonstrated that Ta promotes the rapid formation of uniform Al oxyhydroxide (Al(OH)₃), which protects the substrate in synergy with a Ta₂O₅ oxide film at the initial corrosion. Atomic-scan Kelvin probe force microscopic results demonstrated that corrosion production film including Ta₂O₅ oxide reduces the potential difference (from ~41 to ~16 mV) between the matrix and the Ta-rich phase, weakening the micro-cell corrosion.