Reactions of alkaline earth zirconate refractories with titanium alloys

Stefan Schafföner

doi:10.1051/matecconf/202032110012

Abstract

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.

Highlights

A basic problem for the processing of titanium alloys is the reaction with interstitial elements including oxygen, nitrogen and carbon causing their embrittlement [1, 2]
The present study reviewed current research on refractories for titanium alloy processing including melting and casting
The interaction of titanium alloys with refractories must not be considered as a simple redox reactions using Ellingham diagrams

Summary

Introduction

A basic problem for the processing of titanium alloys is the reaction with interstitial elements including oxygen, nitrogen and carbon causing their embrittlement [1, 2]. As early as in the 1930s Kroll investigated CaO as a refractory material for titanium [11], whereas later especially Y2O3, ZrO2, Al2O3 and other rare earth oxides were considered [7]. Several of these studies concluded–depending on the alloy compositions–that oxides such as CaO and Y2O3, or even ZrO2 and Al2O3 should be stable at high temperature [1, 12, 13].

Results

Conclusion