Sliding wear behaviour of FeCr2VW0.3 refractory medium-entropy alloy (RMEA) at elevated temperatures and associated wear mechanisms

This study presents a comprehensive investigation of the short-term isothermal oxidation behaviour and tribological performance of a FeCr 2 VW 0.3 refractory medium-entropy alloy (RMEA) with dual BCC phases from room temperature (RT) to 650 o C. The RMEA exhibits excellent oxidation resistance below 550 o C, while noticeable oxidation occurs at 650 o C. Both friction coefficient and specific wear rate decrease when temperature is increased from RT to 650 o C; notably, the wear rate at 650 o C is reduced to approximately 3.85% of that at RT. Surface profilometry and SEM observations reveal obviously smoother worn surfaces at elevated temperatures, accompanied by a marked reduction in spallation and delamination and the formation of a relatively continuous and compact tribo-layer. SEM and TEM cross-sectional analyses identify three distinct regions along the depth direction at all temperatures: a topmost tribo-layer, a middle severe plastic deformation region, and a lower less deformed region. With increasing the temperature, the topmost layer evolves from a porous tribo-layer composed of mixed wear debris and oxides at RT to a relatively dense and continuous protective tribo-layer at 650 o C. Moreover, at RT, the severe plastic deformation region consists of nanograined BCC1 phase mixed with fractured coarse-grained BCC2 phase, whereas crack density within the BCC2 phase decreases markedly at 650 °C while the BCC1 phase remains nanograined. The superior thermal-mechanical properties of the alloy, combined with the formation of a stable tribo-layer, lead to a transition in the wear mechanisms from abrasion, plastic deformation, delamination and spallation dominated wear at RT to oxidative and adhesive wear at elevated temperatures.