Deoxidation of NiTi alloy melts using metallic barium

Abstract

The deoxidation behavior of NiTi alloy melts with metallic barium was investigated. Metallic barium was added to the NiTi alloy melts held in lime (CaO) crucibles at 1673 K, and the concentrations of oxygen, barium and calcium in the melts were quantitatively measured. The oxygen content in a raw NiTi alloy bar was 660 ppm, and the oxygen content in the NiTi alloy melts just before barium addition was around 1100 ppm. Oxygen was introduced into the melts by the dissolution of lime during melting. The addition of barium lowered the oxygen content in the melts with the formation of deoxidation product, which might be barium oxide. The oxygen content was measured to be around 350 ppm 120s after barium addition. The barium and calcium contents were less than 10 ppm and 12 ppm, respectively, indicating that the deoxidation product was removed from the melts in a very short period of time. These results suggest that barium is an effective deoxidation element for NiTi alloy melts. Furthermore, the interaction between oxygen and barium cannot be ignored in thermodynamic considerations of the deoxidation process. © 2008 The Japan Institute of Metals.