Electrochemical dissolution behavior of Ti-45Al-2Mn-2Nb+0.8 vol% TiB2 XD alloy in NaCl and NaNO3 solutions

Electrochemical machining is an effective method for the processing of Ti-45Al-2Mn-2Nb+0.8 vol% TiB2 XD (or TiAl 45XD) alloys due to the absence of tool wear and the high material removal rate. This study investigated the electrochemical dissolution behavior of TiAl 45XD in NaNO3 and NaCl solutions, explaining the unique phenomena during the dissolution. The polarization curves, open-circuit potentials and material removal rate (ηω-j curves) were measured. It is found that the lamellar colonies are fully exposed after the electrochemical polarization in NaCl solution and that only some insoluble TiB2 disperse on the specimen surface in NaNO3 solution. The ηω-j curves reveal an unusual dissolution behavior of TiAl 45XD. Dissolution experiments were then carried out at different current densities and corrosion times. The corroded specimens were examined and analyzed using a surface-finish measuring instrument, scanning electron microscope and energy-dispersive X-ray spectroscopy. The results indicate that the surface quality is higher in NaNO3 solution than in NaCl solution because the specimen surface suffers from the pitting and severe localized corrosion and then forms many micro-protrusions in NaCl solution. It is also found that the micro-protrusion plays an important role in the electrochemical dissolution behavior of TiAl 45XD. Finally, qualitative models for the electrochemical dissolution behavior of TiAl 45XD in NaNO3 and NaCl solutions were proposed.