AlCoCrFeNi-x ZrO2 (x = 0, 5, and 10 (wt. %)) high entropy alloy (HEA) matrix composites were prepared by mechanical alloying (MA) and spark plasma sintering (SPS) methods. Microstructural studies showed that the prepared samples mainly consisted of FCC and BCC phases. Also, small contents of Al-rich and Cr-rich phases were observed. According to microhardness analysis, the addition of 10 wt% monoclinic zirconia enhanced the hardness of FCC and BCC phases from 3.42 to 4.48 GPa and 7.00 to 8.52 GPa, respectively. The wear rate calculations showed that using 5 wt% monoclinic zirconia only slightly improved the wear resistance compared to AlCoCrFeNi HEA sample, due to a balance between the positive effect of zirconia addition and the negative effect of BCC phase decrement. However, the wear resistance was considerably enhanced with increasing zirconia content to 10 wt%. Improved H/E ratio of BCC and FCC phases and the reinforcing effect of zirconia particles in this sample are the main effective factors in the enhancement of wear resistance of AlCoCrFeNi-10 wt% ZrO2 sample. In all samples, there were four wear mechanisms including abrasive, adhesive, oxidation, and delamination.
