The oxidation behavior of Ti1.5NbVAlx lightweight medium-entropy alloys in dry air at 800C

Lightweight refractory high/medium-entropy alloys show promise as high temperature alloys for various applications. However, the exact mechanism of high temperature oxidation in these alloys remains unclear. This study focuses on investigating the oxidation behavior of four Ti1.5NbVAlx lightweight RMEAs in dry air at 800 degrees C, where x = 0.25, 0.5, 0.75, 1. The oxidation kinetics of alloys with different Al concentrations displayed varying degrees of mass changes, with the oxidation rate decreasing as the Al concentration increased. The Al0.25 and Al0.5 alloys experienced catastrophic oxidation failure around 5 h, which can be attributed to the high expansion rate of Nb2O5 and the volatilization of V2O5. The formation process of the oxide layer was analyzed in detail. It was found that the oxide layer of the alloy with low Al concentration was loose and porous, with TiNb2O7, TiO2, and Nb2O5 oxides dominating. Additionally, an internal oxide layer was also observed. As the Al content increased, the oxide layer became gradually denser and the contents of AlNbO4 and Al2O3, which have a protective effect, are gradually increased. After 15 h of oxidation, the oxide layer of the Al1 alloy exhibited an interlayer structure consisting of TiO2 intercalated with Nb2O5, V2O5, TiNb2O7, and AlNbO4. This interlayer structure enhances the adhesion of the oxide layer. This study serves as an important reference for the development and practical application of lightweight refractory high -entropy alloys.