Dual mechanisms of grain refinement in a FeCoCrNi high-entropy alloy processed by high-pressure torsion

Abstract

An equiatomic FeCoCrNi high-entropy alloy with a face-centered cubic structure was fabricated by a powder metallurgy route, and then processed by high-pressure torsion. Detailed microscopy investigations revealed that grain refinement from coarse grains to nanocrystalline grains occurred mainly via concurrent nanoband (NB) subdivision and deformation twinning. NB–NB, twin–NB and twin–twin interactions contributed to the deformation process. The twin–twin interactions resulted in severe lattice distortion and accumulation of high densities of dislocations in the interaction areas. With increasing strain, NB subdivision and interactions between primary twins and inclined secondary stacking faults (SFs)/nanotwins occurred. Secondary nanotwins divided the primary twins into many equiaxed parts, leading to further grain refinement. The interactions between secondary SFs/nanotwins associated with the presence of Shockley partials and primary twins also transformed the primary twin boundaries into incoherent high-angle grain boundaries.

Microstructure, Texture, and Strength Development during High-Pressure Torsion of CrMnFeCoNi High-Entropy Alloy

“…The generally low texture strength may be also caused by twinning. In addition to twinning, in CrFeCoNi MEA Wu et al [31] observed nanobands and attributed the significant grain refinement to concurrent nanoband subdivision and deformation twinning. Instead of mechanical twinning, during HPT at LNT a strain-induced phase transformation takes place.…”

Segregation mediated heterogeneous structure in a metastable β titanium alloy with a superior combination of strength and ductility

“…The β phase in regions rich in Mo and W was heavily stabilized, so the high strain induced by cold rolling was accommodated by extensive dislocation activity, such as dislocation multiplication, accumulation, interaction, tangling, and spatial rearrangement. The dislocation cell structure subdivided a grain into many fine grains at the nanometre scale 13 , 31 , 32 , 43 – 45 . In contrast, in the β phase regions containing fewer β stabilising elements, the deformation strain was accommodated by martensite transformation 13 , 32 , 43 , 44 , 46 .…”

Effective Surface Nano-Crystallization of Ni2FeCoMo0.5V0.2 Medium Entropy Alloy by Rotationally Accelerated Shot Peening (RASP)

“…The deformation mechanisms commonly found in conventional metallic materials, such as dislocation slip and deformation twinning, also play important roles in HEAs and MEAs. However, attributed to the low stacking-fault energy (SFE), short-range ordering effect and local elemental fluctuations, dislocation slip and deformation twinning can be very chaotic in HEAs and MEAs during plastic deformation [ 6 , 20 , 21 , 22 , 23 , 24 , 25 ]. It is well known that the propensity for deformation twinning is inversely proportional to the SFE.…”

“…It is well known that the propensity for deformation twinning is inversely proportional to the SFE. The SFE of the Cantor HEA is at the lower bond ~20–25 mJ/m 2 [ 25 ]. Thus, the presence of high densities of deformation twinning is found to be a major mechanism of the plastic strain in the Cantor HEA.…”

“…Recently, Wu et al used HPT to process an FeCoCrNi HEA, and significant grain refinement was realized via complicated concurrent nano-band subdivision and high-order hierarchical twinning mechanisms [ 25 ]. In addition, a high strain rate deformation may also facilitate grain refinement in medium-entropy alloy [ 40 , 41 ], but the relevant research is limited.…”