Effect of Mo content on the microstructure and properties of Al 0.5 Fe 2 CrMnNiMo x high entropy alloy

The development of high-entropy alloys (HEAs) is advancing towards achieving high strength, excellent high-temperature functional properties, and economic feasibility to meet the new demands placed on materials by industry. In present study, a cost-effective Co-free Al 0.5 Fe 2 CrMnNi HEA is used as matrix alloy, and Mo is added as an alloying element to design a series of Al 0.5 Fe 2 CrMnNiMo x (x=0, 0.3, 0.4, 0.5, molar ratio) HEAs with high strength and outstanding wear resistance. The effect of Mo content on the phase transition, microstructure, mechanical properties, wear performance at room and elevated temperature are explored in detail. The XRD patterns indicate that the crystal structure of Al 0.5 Fe 2 CrMnNi HEA includes ordered B2 phase, disordered BCC phase as well as FCC phase. After the addition of Mo, the crystal structures of HEAs transform into FCC, ordered B2 and σ phases. A transition of the microstructure from a typical columnar dendrite to a honeycomb dendrite can be observed from the microstructural morphologies after adding Mo. Attributed to the co-existence of B2 and σ phases, HEAs with the addition of Mo exhibit high compressive strengths but low strain due to the high level of precipitation of the σ-phase. Besides, the investigation on the wear behavior shows that HEAs with the addition of Mo have low specific wear rate and exhibit the same wear mechanisms, i.e., abrasive and oxidative wear. However, the oxidized glaze layer tends to fracture and then form abrasive debris at high temperatures, resulting in the friction performance of HEAs being inferior to that at room temperature. In general, the addition of Mo in Co-free Al 0.5 Fe 2 CrMnNi HEA contributes to the excellent mechanical properties and wear resistance.