Microstructure and Properties of Al0.5CoCrCuFeNiTix (x=0–2.0) High-Entropy Alloys

High-entropy Al0.5CoCrCuFeNiTix alloys are synthesized using the well-developed arc-melting and casting method. The molar ratio (x) of titanium is varied from 0 to 2.0. The microstructure, hardness and wear resistance of the alloys are investigated. The alloys exhibit simple FCC, BCC, CoCr-like and Ti2Ni-like phases. For a small addition of titanium, the alloys form a monolithic FCC solid-solution phase. Two phases of (beta)1 and (beta)2 based on BCC appear at the titanium content of x=0.4 and the (beta)1 phase becomes ordered at x=1.4. With the increase of titanium content, copper segregates to the interdendrite region in which nanoprecipitates form. A CoCr-like phase forms when x ranges from 0.8 to 1.2. Ti2Ni-like phase forms when the titanium content exceeds x=1.0. The hardness value increases with titanium content. The alloys with lower titanium content exhibit similar wear resistance to Al0.5CoCrCuFeNi. The wear resistance is rapidly improved at titanium contents from 0.6 to 1.0, and reaches a maximum at x=1.0. This is followed by a gradual decrease with further increase of the titanium. The mechanisms behind the strengthening and wear resistance of the alloys are discussed.