CHANGES IN OXYGEN CONTENTS OF TITANIUM ALUMINIDES BY VACUUM INDUCTION, COLD CRUCIBLE INDUCTION AND ELECTRON-BEAM MELTING

Fundamental studies on the process of melting titanium aluminides, TiAl, have been pursued from the viewpoint of contamination. Three processes-vacuum induction melting (VIM) with a calcia crucible, cold crucible induction melting (CCM) with a water-cooled copper crucible, and electron beam melting (EBM), -were investigated and compared to determine the behavior of impurity elements, especially oxygen. Experiments using the conventional VIM method revealed that an increase in oxygen content from the calcia crucible during melting was unavoidable. With CCM, oxygen content did not change, while in EBM, it decreased abruptly with the evaporation of aluminum; the aluminum segregation, however, was found accumulated in ingots. The cleanest ingot of 0.02 mass% oxygen was obtained using the combined processes of EB and CCM (EB-CCM). Mechanical properties of the ingots were also examined, and elongation of up to 1.0% was recognized at ambient temperature.