Oxidation of neodymium precipitates in a Ti6Al4V2Nd alloy in sodium chloride solution

摘要

The corrosion properties of a neodymium modified titanium alloy, Ti6Al4V2Nd were investigated in 1.5wt% NaCl and compared with Ti6Al4V. The modified alloy contains neodymium precipitates mainly located at grain boundaries. Ti6Al4V2Nd differs in corrosion behavior from Ti6Al4V by the oxidation of the neodymium precipitates. Electrochemical investigation by polarization measurements and cyclic voltammetry indicate that the precipitates undergo an oxidation process in the early stages of exposure. This is confirmed by SEM investigation and atomic force microscopy (AFM) investigation. Scanning Kelvin probe force microscopy (SKPFM) and electrochemical AFM (EC-AFM) investigation were used to investigate localized corrosion phenomena. SKPFM shows clearly a high Volta potential difference between the precipitates and the matrix, indicating that the precipitates act as local anodes during corrosion. EC-AFM shows that during exposure to NaCl solution the precipitates undergo a strong change in height, owing their oxidation with subsequent formation of an oxide or oxyhydride due to their low stability in NaCl solution.