THE EFFECT OF MOULD PRE-HEAT TEMPERATURE AND CASTING DIMENSIONS ON THE REACTION BETWEEN TiAl ALLOY AND THE ZIRCONIA INVESTMENT CASTING MOULDS

摘要

The casting of titanium based alloys presents considerable problems, including the extensive interactions that occur between the metal and refractory. In this work, CaO stabilised zirconia was used as a primary coat material on the investment casting mould. The reaction between the zirconia face-coat and a Ti-46Al-8Nb-1B alloy was evaluated at three mould pre-heating temperatures: 500℃, 1000℃ and 1200 ℃. The effect of casting dimensions on interaction was also included in this work and the computer simulation of metal cooling profiles was carried out to assist the analysis. Higher mould pre-heat temperature and larger casting dimensions enhanced the interaction between the shell and the TiAl alloy associated with longer metal solidification time. During the high temperature casting process, not only were O and Zr observed penetrating into the metal from the decomposition of the face-coat materials, but also Si which had penetrated from the backup coat was found to have interacted with the metal.