Native oxidation resistance of Al20Nb30Ta10Ti30Zr10 refractory complex concentrated alloy (RCCA)

The native oxidation resistance of an Al20Nb30Ta10Ti30Zr10 (at.%) refractory complex concentrated alloy (RCCA) was evaluated at 1000 degrees C in air. Oxidation tests revealed that the alloy exhibits linear oxidation kinetics out to 4 h of oxidation, with an adherence to parabolic, diffusion-controlled oxidation from 4 to 100 h. This transition was ultimately attributed to the formation of an outer oxide consisting primarily of TiO2 and Ti7Al2O15 layers. The 100 h oxide product contained multiple internal layers, but the overall oxidation kinetics was proposed to be controlled by the outer composite oxide layer. While this layer was morphologically continuous, it consisted of a non-continuous mixture of NbAlO4, ZrO2, Ti7Al2O15, and Ta2Nb4O15. The observed oxide scales are discussed relative to the oxidation behaviors of less-complex alloys. (C) 2019 Elsevier B.V. All rights reserved.