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−xHf_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)₂Hf-type Laves phase and tailors the microstructure from a body-centered cubic (BCC) single-phase structure to a hypoeutectic structure. An increased hardness from ~ HV 512.3 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 × 10⁻⁵ to 0.97 × 10⁻⁵ m³·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.