The precipitated strengthening of Eta phase on the non-equimolar CoCrNiTi medium-entropy alloys (Invited Speaker)

In high-entropy alloys (HEAs) and traditional alloys, η-Ni₃Ti precipitation is usually avoided due to its brittleness. However, studies have demonstrated that using thermal mechanical process to control precipitates in nano-size is an effective approach to overcome strength-ductility dilemma. Herein, we focus on a non-equimolar CoCrNiTi medium-entropy alloy (MEA) which consists of face-centered cubic (FCC) matrix and Ni₃Ti η phase precipitation. The microstructures of η precipitation are observed to achieve uniform and nano-scale morphology. Hardness and tensile test are also conducted to testify the mechanical properties. In addition, a novel processing is utilized and compared with conventional cold-rolling and aging procedure. The results indicate that our technique brings about more uniformly distributed precipitations and higher hardness than traditional ones. Moreover, the alloys are 200 to 300 MPa higher in yield strength (YS) and ultimate tensile strength (UTS) without losing ductility. The causes of the superior properties are also discussed.