Microstructure and Properties of Al_0.5CoCrCuFeNiTi_x (x=0–2.0) High-Entropy Alloys

抄録

High-entropy Al_0.5CoCrCuFeNiTi_x 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 β₁ and β₂ based on BCC appear at the titanium content of x=0.4 and the β₁ phase becomes ordered at x=1.4. With the increase of titanium content, copper segregates to the interdendrite region in which nano-precipitates 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 Al_0.5CoCrCuFeNi. 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.