Oxidation behaviors of CrNb, CrNbTi, and CrNbTaTi concentrated refractory alloys

The 1200 °C oxidation behaviors of CrNb, CrNbTi and CrNbTaTi are reported. All alloys formed some combination of BCC and Laves phases. However, additions of Ti produced a unique inflection point where the microstructure inverts to a Ti-rich BCC matrix with Laves phase precipitates. Further additions of Ta to CrNbTi were found to increase the overall phase fraction of BCC phase. The oxidation kinetics for CrNb and CrNbTi were similar and nearly parabolic throughout the duration of exposure. CrNbTaTi exhibited inferior oxidation kinetics and mixed mode behavior throughout oxidation testing. All alloys formed intricate multi-phase oxide structures, consisting of a combination of both simple and complex oxides. The resulting microstructures are characterized using a variety of analytical techniques and the results are discussed relative to modeling predictions using ab initio density functional theory (DFT).