| 초록 |
Industrial applications of most alloys is limited because of the strength-ductility tradeoff experienced with a grain reduction down to the ultrafine regime. The strength-ductility tradeoff in most alloys has limited their use in industrial application where both properties are required. However, this presentation will feature recent development of (CoCrMnNi)50Fe50 medium entropy alloy that has a remarkable combination of high strength and ductility after annealing at 600°C. The fabrication of the alloy was done using vacuum arc melting method. The ingot was homogenized at 1000°C for 24 h followed by cold rolling with a 90% thickness reduction to obtain plates of 1.5 mm thick. Phase identification for samples annealed at 500ºC, 600°C, 700°C and 800°C for 30 min was done using X-ray diffraction. It was confirmed that all the samples contained a single phase face-centered cubic structure and the X-ray diffraction patterns indicated that recrystallization seemed to start from 600°C. Subsequent heat treatment was done at 600°C for between 3 min and 24 h. The microstructure of all samples were characterized using scanning electron microscope on a backscatter scanning electron mode. A remarkable ultrafine grain size of 846 nm was achieved after annealing for 1 h. To investigate the mechanical properties of both partially and fully recrystallized samples, tensile tests were conducted ambient temperature with initial strain rate of 8.3×10-4 s -1. A fully recrystallized sample showed a yield strength of 550 MPa and ultimate tensile strength of 700 MPa with total elongation of 51%, which showed excellent combination of high strength and ductility as a single FCC MEA |
