Microstructure and properties of a CoCrFeNiMn high-entropy alloy processed by equal-channel angular pressing

Abstract

A CoCrFeNiMn high-entropy alloy (HEA) was processed by equal-channel angular pressing (ECAP) for up to four passes at 673 K and the results show that the strength increases gradually with increasing straining up to ~1 GPa with an elongation to failure of ~35% after four passes of ECAP. In this condition, the microstructure is a single-phase ultrafine-grained (UFG) CoCrFeNiMn HEA with an average grain size of ~100 nm and a high dislocation density. This UFG HEA was subjected to post-deformation annealing (PDA) at temperatures of 673-1073 K for 60 min and it is shown that the hardness increases slightly due to precipitation to 773 K and then decreases to 1073 K due to a combination of recrystallization, grain growth and a dissolution of precipitates. The formation of brittle σ-phase precipitates improves the strength significantly but with a minor decrease in ductility. Annealing at the peak temperature of 773 K produces a very high yield strength of ~1015 MPa and an ultimate strength of ~1080 MPa together with an excellent elongation to failure of ~30%. An analysis of the data shows that grain boundary strengthening is the most important strengthening mechanism in these ECAP samples both before and after PDA.

Effect of Ti on phase stability and strengthening mechanisms of a nanocrystalline CoCrFeMnNi high-entropy alloy

“…7(d). The formation of precipitates with similar composition was reported earlier in the grain boundaries of heavily deformed CoCrFeNiMn HEAs [10,26,27]. Chemical analyses were undertaken of these two regions containing the nano-precipitates and the secondary larger precipitates as illustrated in Figs 8 and 9, respectively.…”

Effect of carbon content and annealing on structure and hardness of CrFe2NiMnV0.25 high-entropy alloys processed by high-pressure torsion

“…Several reports are now available describing the influence of HPT processing on HEAs [15][16][17][18][19][20][21][22][23][24] and there is also a single report documenting the processing of an HEA by ECAP [25]. It was shown earlier that processing a CoCrFeNiMn high-entropy alloy by HPT leads to significant hardening and grain refinement and, in addition, post-deformation annealing (PDA) of the nanocrystalline CoCrFeNiMn HEA provides an excellent combination of high strength and good ductility [19].…”

Influence of Annealing on Microstructure and Mechanical Properties of a Nanocrystalline CrCoNi Medium-Entropy Alloy

“…The so-called Cantor-alloy, that consists of CrMnFeCoNi in an equiatomic composition, has been intensively examined over the last years encompassing many significant mechanical [ 3 , 4 , 5 , 6 , 7 ] and various physical aspects [ 8 , 9 , 10 , 11 ]. Recently, these investigations have been extended to the nanocrystalline (NC) grain-size regime that is accessible by means of severe plastic deformation (SPD) [ 12 , 13 , 14 , 15 , 16 , 17 ]. After transformation of the coarse-grained (CG) pre-material into a NC-structure the pure single-phase solid solution character was maintained while combined with a substantial increase of strength.…”