Removal of Oxygen in Ti–Si Melts by Arc-Melting

Abstract

Oxygen removal from Ti–Si melts (Si: 9.1–30 mass%) during arc melting was investigated. High-purity Si was added to either Ti with a high oxygen content (High O Ti, O: 1.6 mass%) or commercially pure Ti (CP Ti, O: 0.104 mass%) melted under Ar or He gas flow conditions at atmospheric pressure. At Si additions of 23 mass% and 30 mass%, the oxygen content of the Ti–Si ingots decreased. After melting, Si and amorphous SiO₂ powders were observed in the chamber, which suggested that the oxygen in the melts was removed in the form of SiO gas. The oxygen content of the Ti–Si ingots after melting varied as a function of position within the ingot; the residual oxygen content was lowest in the top section of the ingots and highest in the bottom section. Under the Ar gas flow, the oxygen content of the High O Ti–30Si ingot decreased to 0.136 mass% and 0.609 mass% in the top and center sections of the ingot, respectively; similarly, the oxygen content of the CP Ti–30Si ingot decreased to 0.030 mass% and 0.051 mass% in the top and center sections, respectively. After melting under He gas flow, the oxygen contents of the CP Ti–30Si ingot in the top, center, and bottom sections were 0.020 mass%, 0.021 mass%, and 0.029 mass%, respectively. Better uniformity of oxygen distribution in the ingots was achieved under the He gas flow than under the Ar gas flow because the melted region is extended in the depth direction by using He gas. During melting, no significant evaporation of Ti and Si occurred, which is an advantage of arc melting that operates at atmospheric pressure over electron beam melting that occurs in vacuum.