Reactions of alkaline earth zirconate refractories with titanium alloys

The severe reactivity of titanium alloys with ceramics is a major challenge for their processing. Up to now refractories to melt and cast titanium alloys are selected on the basis of a low Gibbs energy of formation. This kind of selection assumes that an oxide should be stable if its Gibbs energy of formation is lower than the one of any titanium (sub)oxide. The present contribution reviews that these models trying to explain the stability of ceramic materials in contact with titanium alloys are often misleading. By contrast, a dissolution and evaporation based reaction model is more appropriate to describe the reaction of high temperature ceramics with titanium alloys. These explanations were exemplified by research findings of high temperature reactions of titanium alloys with calcium oxide and yttrium oxide. Based on the discussion on calcium and yttrium oxide, the reactions of alkaline earth zirconates such as calcium and barium zirconate with titanium alloys were discussed. The reaction of alkaline earth zirconates is also highly dependent on the titanium alloy composition. It was also demonstrated that not only thermodynamics but also kinetics should be considered to evaluate refractories for titanium processing.