Annealing effect on plastic flow in nanocrystalline CoCrFeMnNi high-entropy alloy: A nanomechanical analysis

Abstract

The influence of annealing on the constitutive stress-strain response of nanocrystalline (nc) CoCrFeMnNi high-entropy alloy (HEA) was investigated through a series of nanoindentation experiments using five different three-sided pyramidal indenters. The nc HEA, produced by high-pressure torsion (HPT), was subjected to annealing at 450 o C for 1 and 10 h. Microstructural analysis using transmission electron microscopy (TEM) showed that three different nano-scale precipitates (NiMn-, FeCo-, and Co-rich phases) form in the primary single-phase matrix of nc HEA after annealing. The strain-dependent plastic flow response of nc HEA pre-and post-annealing was estimated using the indentation strain and constraint factor, revealing a significant strain softening in nc HEA, which becomes pronounced after annealing. TEM analysis of the deformed material underneath the indenter suggests that the plastic deformation aids in the dissolution of the annealing-induced intermetallic precipitates, which could be the mechanism for the pronounced softening. The dissolution mechanismwas 2 rationalized by the destabilization of precipitates during plastic deformation due to the increase in interface energy.

Entropic phase transformation in nanocrystalline high entropy oxides

“…We therefore attribute the change in phase evolution behavior to the high grain boundary volume found in the nanocrystalline HEO, which will enhance the diffusion kinetics and alter the secondary-phase morphology. Our observed length-scale dependent phase behavior exhibits similarities to the precipitation behavior in some nanocrystalline HEA materials [15]. Further work is ongoing to explore these length-scale effects in more detail.…”

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.…”