TiNbCr Multi-Principal Element Alloy Oxidation Behavior in Air at 800–1000 °C

The isothermal and cyclic oxidation behavior of a multi-principal element (MPE) TiNbCr alloy at 800–1000 °C in air was studied and compared to Co-based alloy 188. The phase constitution of the MPE alloy consisted of a Nb-rich body-centered cubic (BCC) matrix and Cr-rich Laves precipitates. While isothermal tests conducted at 800 °C led to the formation of a complex mixture of Nb, Ti and Cr oxides, tests at 900 and 1000 °C resulted in the formation of an innermost Cr₂O₃-rich scale layer which provided improved oxidation resistance. However, for all exposure temperatures, the scaling kinetics of the alloy were linear and therefore deemed non-protective. In contrast, alloy 188 exhibited parabolic scaling kinetics and smaller mass gain per area than the MPE alloy. The similarity between isothermal and cyclic test results for the MPE alloy confirmed that the scale does not offer much protection. Additionally, for all tests, there was extensive internal oxidation and nitridation.