Cathodic deoxygenation of the alpha case on titanium and alloys in molten calcium chloride

The oxygen-enriched alpha case on titanium and alloys was successfully deoxygenated to satisfactory levels by electrolysis in molten CaCl2, in which the cathode was made from the metal to be refined. The oxygen distribution in the metal before and after electrolysis was characterized by microhardness tests, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX). The electrolysis has been carried out at voltages sufficiently below that for the decomposition of CaCl2, and the results obtained suggest that the alpha case deoxygenation follows a simple oxygen ionization mechanism in which the oxygen in the metal is simply ionized at the cathode/electrolyte interface, dissolves in the molten salt, and then discharges at the anode. It is shown that by applying the electrochemical method, the alpha cases on both commercially pure titanium (CP Ti) and the Ti-6Al-4V alloy can be effectively deoxygenated. In particular, due to the removal of oxygen, the original alpha case (single phase) on the Ti-6Al-4V alloy has been converted back to the two-phase microstructure.