A Hf-doped dual-phase high-entropy alloy: phase evolution and wear features

Initially defined high entropy alloys (HEAs) usually exhibit a single-phase solid-solution structure. However, two and/or more types of phases in HEAs possibly induce the desired microstructure features, which contribute to improving the wear properties of HEAs. Here, we prepare a series of (AlCoCrFeNi)(100-x)Hf-x (x = 0, 2, 4 and 6; at%) HEAs and concern their phase compositions, microstructures and wear properties. Hf leads to the formation of (Ni, Co)(2)Hf-type Laves phase and tailors the microstructure from a body-centered cubic (BCC) single-phase structure to a hypoeutectic structure. An increased hardness from similar to HV 512.3 to similar to HV 734.1 is due to solid-solution strengthening, grain refinement strengthening and precipitated phase strengthening. And a few oxides (Al2O3 + Cr2O3) caused by the wear heating contribute to an 85.5% decrease in wear rate of the HEA system from 6.71 x 10(-5) to 0.97 x 10(-5) m(3).N-1.m(-1). In addition, Hf addition changes the wear mechanism from abrasive wear, mild oxidative wear and adhesive wear to oxidative wear and adhesive wear.