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.
Highlights
The plastic deformation mechanisms of High-entropy alloys (HEAs) could be different from that of conventional alloys, since HEAs have highly distorted lattice structures due to the different atomic sizes and chemical bonds of their constituent elements[22]
We performed a systematic investigation of the microstructural evolution of a FeCoCrNi HEA introduced by high-pressure torsion (HPT)
Depending on the microstructural characteristics observed in this study and the corresponding equivalent strain, the HPT-induced microstructural evolution process was divided into four deformation stages with increasing strain
Summary
The plastic deformation mechanisms of HEAs could be different from that of conventional alloys, since HEAs have highly distorted lattice structures due to the different atomic sizes and chemical bonds of their constituent elements[22]. Tang et al reported that a nanostructure of Al0.3CoCrFeNi alloy processed by HPT processing has a high incremental hardness, and subsequent annealing at appropriate temperatures gave an ordered BCC secondary phase with an additional increase in hardness[24]. Yu et al showed that the plastic deformation mechanisms of an Al0.1CoCrFeNi FCC HEA induced by HPT at room temperature include dislocation slip at low strains and twinning at high strains[16]. FeCoCrNi HEA is a stable single FCC solid solution with high toughness even at cryogenic temperatures[25,26]. He et al reported that the FeCoCrNi HEA is metastable at intermediate temperatures[27]. The investigation presents detailed information on the grain refinement mechanisms of the HEA, and provides fundamental basis for the applications of FeCoCrNi based HEAs
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