Mechanical properties and tribological behavior of Al0.5CoCrFeNb0.5Ni high-entropy alloy at high temperatures

The high-temperature mechanical properties and tribological behavior of the Al0.5CoCrFeNb0.5Ni high-entropy alloy (HEA) were investigated. The results show that Al0.5CoCrFeNb0.5Ni HEA are composed of FCC, BCC and Laves phases. The hardness is about 572 HV at room temperature and decreases slightly at high temperatures, still maintaining a high value (> 350 HV) at 900 °C. The yield strength is nearly 2000 MPa at room temperature and tends to decrease with rising temperature (800-1200 °C). The observation of the microstructure after the hot compression tests and the evaluation of the true stress-strain curves illustrate that the softening mechanism is primarily dynamic recrystallization, which occurs mainly in the FCC and BCC phases. The degree of wear increases and then decreases from 200 °C to 800 °C. The best wear resistance was observed at 800 °C, showing the maximum friction coefficient and the minimum wear rate, which was attributed to the increased oxidation that formed oxide layers mainly consisting of Cr2O3 to protect the wear surfaces. The wear mechanism of alloys is affected by temperature. Below 400 °C the wear is mainly abrasive and adhesive wear, at temperatures above 600 °C, the wear transitions from abrasive to oxidative wear, and at 800 °C the wear changes to oxidative wear.