Changes of Oxygen Content in Molten TiAl Alloys as a Function of Superheat during Vacuum Induction Melting

Experimental studies on the melting process of titanium aluminum alloy have been pursued from the viewpoint of contamination. TiAl alloys were prepared with vacuum induction melting (VIM) in calcia crucibles at 1873 K and 1923 K in order to determine the behavior of the oxygen content as a function of temperature, time and frequency of power. The experiment results showed that alloys were uncontaminated except for the increasing of oxygen content which was introduced from the reaction CaO(s)=Ca(in TiAl)+O(in TiAl), and the standard Gibbs energy of the reaction was determined to be ΔG0=274000−102.8T (J/mol). Oxygen content increased slowly with the melting time by about 50×10−6 wt pct/min, and decreased with induction melting frequency. Lower superheat and higher melting frequency can be used to reduce oxygen content increasing rate.