Effect of annealing on mechanical properties of a nanocrystalline CoCrFeNiMn high-entropy alloy processed by high-pressure torsion

Abstract

A CoCrFeNiMn high-entropy alloy (HEA) was processed by high-pressure torsion (HPT) under 6.0 GPa pressure up to 10 turns at room temperature. It is shown that there is a gradual evolution in hardness with increasing numbers of turns but full homogeneity is not achieved even after 10 turns. Microhardness measurements reveal that the material reaches a saturation hardness value of ~4.41 GPa and in this condition the microstructure shows exceptional grain refinement with a grain size of ~10 nm. An ultimate strength value of ~1.75 GPa and an elongation to fracture of ~4% were obtained in a sample processed for 5 turns. The nanostructured HEA was subjected to post-deformation annealing (PDA) at 473-1173 K and it is shown that the hardness increases slightly to 773 K due to precipitation and then decreases up to 1173 K due to a combination of recrystallization, grain growth and a dissolution of the precipitates. The formation of brittle precipitates, especially σ-phase, at 873 and 973 K significantly reduces the ductility. Short-term annealing for 10 min at 1073 K prevents grain growth and leads to a combination of high strength and good ductility including an ultimate tensile strength of ~830 MPa and an elongation to failure of ~65%.

Micro-mechanical and tribological properties of aluminum-magnesium nanocomposites processed by high-pressure torsion

“…In addition, short-term annealing reduces the dislocation density in the grain interior of the UFG material after SPD so that the dislocation storage capability may increase and thus the strain hardening capability is enhanced wand this leads to the possibility of high ductility in the SPD-processed material. There are several recent reports demonstrating the significance of PDA on mechanical properties at RT of HPT-processed materials [51][52][53][54]. Thus, considering the present nanoindentation results reporting a significant enhancement in the strain rate sensitivity after PDA, the MMNC in the Al-Mg system produced by HPT has a great potential for demonstrating both high hardness and superior ductility.…”

CoCrFeMnNi high‐entropy alloy powder with excellent corrosion resistance and soft magnetic property prepared by gas atomization method

“…It is evident that the asatomized powder exhibits a single face-centered cubic phase without any other phases. The crystal structure of the as-atomized powder is consistent with that of the CoCrFeMnNi high-entropy alloy in the bulk or coating form [19,38,39].…”

A high-entropy alloy with hierarchical nanoprecipitates and ultrahigh strength

“…In addition to precipitation strengthening, other strengthening mechanisms are believed to contribute to the ultrahigh strength measured. Because of submicrometer grain sizes, 409 and 227 nm for the fcc and bcc phase, respectively, grain-boundary strengthening is likely to occur ( 23 , 34 ). Furthermore, the bcc phase with ordered B2 structure is usually considered as a hard/strong phase that can result in a high increment in yield strength due to a load transfer mechanism ( 13 , 36 ).…”