High-temperature wear mechanisms and oxidation properties of MoNbTaWTi refractory high entropy alloy prepared by direct laser deposition

Abstract

The MoNbTaWTi refractory high-entropy alloy (RHEA) has attracted significant attention due to its excellent phase stability at elevated temperatures and enhanced mechanical properties at room temperature. However, its high-temperature wear mechanisms and oxidation behavior are not yet well understood. This study aims to investigate the alloy's mechanical properties at room temperature and its oxidation and wear mechanisms at elevated temperatures. The alloy exhibits a typical columnar grain structure with a {112} 〈1−10〉 texture, achieving a peak stress of 1633 MPa and an elongation of 8 %. High-temperature oxidation tests reveal that at 500 °C and 650 °C, the oxidation kinetics follow a parabolic curve for the first three hours, transitioning to a linear rate thereafter. Wear tests show that the average friction coefficient decreases with increasing temperature, likely due to the formation of an oxide glaze. The specific wear volume initially decreases from 400 °C to 600 °C but increases at 600 °C. Microstructural analysis indicates the formation of spalling and delamination in the oxide glaze at 600 °C, which may be caused by cracks induced by material softening at high temperatures, along with a reduced load-bearing capacity of the oxide glaze due to the increased formation of brittle phases like WO₃. Moreover, the alloy exhibits abrasion wear at room temperature, abrasive and oxide wear at 200 °C, oxide wear at 400 °C, and both oxide and fatigue wear at 600 °C.