Effects of oxidation on friction and wear properties of eutectic high-entropy alloy AlCoCrFeNi2.1

Dual phase high-entropy alloys formed by eutectic transformation from the melt (EHEAs), tend to possess a greater balance in strength and ductility as compared to those of conventional single-phase FCC, BCC or HCP HEAs manufactured from similar elements. Properties, including corrosion resistance and good softening-resistance under high-temperature conditions, make them potential candidates for challenging industrial applications. However, few insights on tribological properties of EHEAs at high temperatures are currently available. Our study explored the friction and wear behavior of AlCoCrFeNi2.1 EHEA against Si3N4 by reciprocating pin-on-disc testing, over a wide range of temperature (500–900 °C). High-temperature oxidation behavior was thoroughly examined and found to have a definite influence on wear mechanism of AlCoCrFeNi2.1. For temperatures in the range 500–600 °C, the friction coefficient is roughly at 0.4 and abrasion is dominating wear mechanism. Above 700 °C, there is a transition from abrasive wear to adhesive wear which is associated with prolonged running-in stage, and higher friction coefficient and higher wear rate on the EHEA surface. In-depth analysis revealed that development of oxide scale is the major contributing factor to the change in friction/wear behavior, with the effect becoming more significant above 700 °C.