| Abstract Scope |
Refractory multi-principal element alloys are of interest for their mechanical strength at high temperature, however, rapid oxidation rates limit their use. Equimolar NbTiZr was oxidized at 1250°C in 1%O2 (balance argon) using a resistive heating system for 5 minutes under three thermal cyclic exposure conditions: isothermal, 2x2.5 minutes, and 5x1 minute. While the initial goal of the exposures was to explore oxide spallation, minimal oxide spallation was observed on cooling for all test conditions. However, significant differences in oxide morphology and oxidation rates were observed. The isothermal oxidized samples showed alloy grain boundary oxidation, lamellar Nb and Zr phase separation, templating lamellar oxide growth perpendicular to the surface. The cyclically oxidized samples showed globular phase separation of Zr and Nb, which also acted as a template for oxide microstructure during later cycles. Lower metal consumption during the cyclic oxidation exposures show that initial phase separation morphology significantly affects oxidation rates. |