Microstructures and deformation mechanisms of the medium-entropy alloy (NiCoCr)76(Ni6AlTi)3

作者：Peng, Hanlin^*; Hu, Ling^*; Chen, Junfu; Huang, Siming; Li, Liejun; Yi, Yaoyong; Zhou, Feng; Fang, Weiping; Baker, Ian

来源：Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing , 2022, 849: 143449.

DOI：10.1016/j.msea.2022.143449

• Medium-entropy alloys
• Microstructure
• Mechanical properties
• Strengthening mechanisms
• Deformation mechanisms

The microstructures and deformation mechanisms of the f.c.c. medium-entropy alloy (MEA) (NiCoCr)(76)(Ni6AlTi)(3) has been analyzed after various thermo-mechanical treatments. The solutionized, single-phase MEA, which had a grain size of 93.4 +/- 31.9 mu m, was cold-rolled (CR) to a 80% thickness reduction after which it showed both a high yield strength (YS) of 1539 MPa and a high ultimate tensile strength (UTS) of 1602 MPa, but an elongation to failure, e, of only 16%. The CR MEA was then subjected to one of two heat treatments: (1) the CR MEA was recrystallized at 1100? for 24 h, which produced a single-phase material with 85 +/- 61.7 mu m grain size that exhibited a much lower YS and UTS of 364 MPa and 747 MPa, respectively, but a much greater e of 73%; and (2) the MEA was aged at 700oC for 24 h, which produced a fine-grained (1.1 +/- 0.9 mu m) material and a high volume fraction (0.35) of 12 nm dia. L12 nanoparticles that exhibited an excellent combination of strength and ductility, viz., YS-1501 MPa, UTS-1651 MPa, elongation-26%. The grain boundary strengthening and precipitation strengthening were together estimated to account for-58% of the YS in the latter material. After deformation, the recrystallized MEA contained numerous stacking faults and a Taylor lattice structure containing domain boundaries and microbands, while the aged MEA exhibited numerous stacking faults and sheared particles. The density of low-angle grain boundaries (LAGBs) in the recrystallized MEA increased by 100 times to 2.2 x 10-1 mu m/mu m2 while the density of CSL E3n boundaries decreased by 71% to 7.8 x 10(-3) mu m/mu m(2) after deformation. In contrast, the density of LAGBs in the aged MEA increased by 5 times to 2.6 mu m/mu m2 while the density of CSL E3n boundaries decreased by 57% to 0.6 mu m/mu m(2) after deformation.