AlCrFeNiX (X = Cu, Si, Co) high entropy alloys (HEAs) were produced by mechanical alloying and sintering. The effects of the ?X" additive on the microstructure, hardness, wear, and high-temperature oxidation behavior of HEAs were investigated. Different phases occurred in AlCrFeNiX HEAs depending on the ?X" element. In addition to the BCC phase in all alloys, there are FCC phases in AlCrFeNiCu and AlCrFeNiCo alloys and two different intermetallic phases AlCrFeNiSi alloy. High negative mixing enthalpy values were found to be effective in phase and microstructure formation. In the alloy containing Si, 750 HV micro-hardness was seen as the highest hardness value. In the alloys containing Co and Cu, 450 and 420 HV micro-hardness values were determined, respectively. The best wear resistance and the lowest friction coefficient were seen in the AlCrFeNiSi alloy. In the wear tests performed at different loads, the increasing load increased the wear losses. The isothermal oxidation tests were conducted to HEAs at 1000 ?C for 5, 25, and 75 h. Each HEAs exhibit very well oxidation resistance under the current conditions due to the selective alumina formation on the surface. It was not detected a dramatic difference in terms of oxidation behaviors of HEAs.