A Study on the Mechanical Behavior and Deformation Mechanism of the Aged Ni2CoCr0.5Si0.3Al0.1Ti0.1 Medium Entropy Alloy

Abstract

Purposes A novel type of Ni2CoCr0.5Si0.3Al0.1Ti0.1 medium entropy alloy is designed in this work. Methods Trace amounts of Si, Al, and Ti elements are added to the non-equiatomic ratio NiCoCr-based medium entropy alloy, and dispersed coherent L12 phase precipitation is introduced through aging heat treatment at different temperatures. Findings The results show that the Ni2CoCr0.5Si0.3Al0.1Ti0.1 medium entropy alloy aged at 700 ℃ has the best mechanical properties, with a yield strength of 783 MPa, an ultimate tensile of 1 252 MPa, and an elongation of 41.6%. Compared with the annealed samples, the alloy after aging treatment is increased in yield strength by 310 MPa. Further analysis of the initial microstructure of the alloy aged at 700 ℃ reveals the presence of coherent L12 phase structure and trace amount of intermetallic compound Ni16Ti6Si7 phase. Meanwhile, because of the severe deformation through cold rolling and the short time of annealing treatment, trace stacking faults, nano stacking fault networks, Lomer-Cottrell locks, and dislocation pinning phenomena are found in the initial structure. The geometrically necessary dislocation exhibits a uniform distribution during the stretching process, and the main deformation mode is dominated by dislocation slip with a stacking fault structure.

Keywords

• medium entropy alloy
• composition design
• aging treatment
• mechanical properties
• precipitation strengthening
• deformation mechanism