Effect of Ti on the wear behavior of AlCoCrFeNi high-entropy alloy during unidirectional and bi-directional sliding wear processes

High-entropy alloys (HEAs) are generally in a solid-solution state, possessing some superior properties over conventional alloys due to their microstructural homogeneity, effective multi-element strengthening and deformation twinning. In the present study, 10 at% Ti was added to an equiatomic AlCoCrFeNi high-entropy alloy, which increased its microstructural inhomogeneity with the formation of distinctive honeycomb-shaped interdendrites. The performances of the AlCoCrFeNi alloy and the Ti-added one, AlCoCrFeNiTi0.5, during unidirectional and bi-directional sliding wear processes were investigated. It was shown that the addition of Ti considerably enhanced the HEA against wear under both the sliding conditions mainly due to the increased hardness. The volume loss decreased during bi-directional sliding, which was further decreased as the sliding direction was reversed more frequently. The decreased wear by bi-directional sliding was attributed to the Bauschinger effect in which defect annihilation (i.e., cancellation of dislocations of opposite signs) occurred with reversal of the wearing stress. The Ti addition did not show much influence on the trend of wear variations with the wearing stress reversal except the magnitude of material loss. By performing wear tests with and without airflow cooling, it was shown that local heating by friction promoted the Bauschinger effect, which could be ascribed to the increase in the dislocation mobility and reversibility at elevated temperatures.