High temperature oxidation behaviors of equimolar NbTiZrV and NbTiZrCr refractory complex concentrated alloys (RCCAs)

Refractory complex concentrated alloys (RCCAs) represent an emerging class of materials that have displayed significant potential for increased mechanical performance at extreme temperatures over conventional refractory alloys and Ni-base superalloys. While limited work has been conducted in this area, several RCCAs have shown remarkable levels of oxidation resistance in comparison to the majority of uncoated commercial refractory alloys. However, the oxidation mechanisms in these types of alloys have not been well understood. This study aims to develop the foundation for understanding RCCA oxidation mechanisms through the systematic evaluation of NbTiZrV and NbTiZrCr, which display vastly different oxidation behaviors. In both cases, the predominant mechanism appeared to be internal oxidation, where a mixture of simple and complex oxides was observed after prolonged oxidation times. This resulted in extended linear oxidation kinetics for the NbTiZrV alloy and linear to near-parabolic oxidation kinetics for the NbTiZrCr alloy. Under this mindset, novel design strategies for promoting increased oxidation resistance in both RCCAs and dilute refractory alloys based on sluggish complex oxides are proposed. [Display omitted] •NbTiZrV and NbTiZrCr RCCAs display a strong tendency for internal oxidation.•Cr promotes parabolic kinetics (NbTiZrCr), but not by continuous Cr2O3 formation.•Tailorable oxidation resistance of RCCAs considering complex oxides is possible.