Microstructure tailoring of Al0.5CoCrFeMnNi to achieve high strength and high uniform strain using severe plastic deformation and an annealing treatment

Abstract

Ultrafine-grained alloys fabricated by severe plastic deformation (SPD) have high strength but often poor uniform ductility. SPD via high-ratio differential speed rolling (HRDSR) followed by an annealing treatment was applied to Al0.5CoCrFeMnNi to design the microstructure from which both high strength and high uniform strain can be achieved. The optimized microstructure was composed of an ultrafine-grained FCC matrix (1.7–2 μm) with a high fraction of high-angle grain boundaries (61 %–66 %) and ultrafine BCC particles (with a size of 0.6–1 μm and a volume fraction of 8 %–9.3 %) distributed uniformly at the grain boundaries of the FCC matrix. In the severely plastically deformed microstructure, the nucleation kinetics of the BCC phase was accelerated. Continuous static recrystallization (CSRX) took place during the annealing process at 1273 K. Precipitation of the BCC phase particles occurring concurrently with CSRX effectively retarded the grain growth of the FCC grains . The precipitation of the hard and brittle σ phase was, however, suppressed. The annealed sample processed by HRDSR with the optimized microstructure exhibited a high tensile strength of over 1 GPa with a good uniform elongation of 14 %–20 %. These tensile properties are comparable to those of transformation-induced plasticity steel. Strengthening mechanisms of the severely plastically deformed alloy before and after annealing were identified, and each strengthening mechanism contribution was estimated. The calculated results matched well with the experimental results.