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

Abstract

The equiatomic face-centered cubic high-entropy alloy CrMnFeCoNi was severely deformed at room and liquid nitrogen temperature by high-pressure torsion up to shear strains of about 170. Its microstructure was analyzed by X-ray line profile analysis and transmission electron microscopy and its texture by X-ray microdiffraction. Microhardness measurements, after severe plastic deformation, were done at room temperature. It is shown that at a shear strain of about 20, a steady state grain size of 24 nm, and a dislocation density of the order of 1016 m−2 is reached. The dislocations are mainly screw-type with low dipole character. Mechanical twinning at room temperature is replaced by a martensitic phase transformation at 77 K. The texture developed at room temperature is typical for sheared face-centered cubic nanocrystalline metals, but it is extremely weak and becomes almost random after high-pressure torsion at 77 K. The strength of the nanocrystalline material produced by high-pressure torsion at 77 K is lower than that produced at room temperature. The results are discussed in terms of different mechanisms of deformation, including dislocation generation and propagation, twinning, grain boundary sliding, and phase transformation.

Effect of Stacking Fault Energy on Microstructure and Texture Evolution during the Rolling of Non-Equiatomic CrMnFeCoNi High-Entropy Alloys

“…Within the resolution of X-ray diffraction, no transformation to hexagonal martensite could be detected after Cryo-R. Such a phase transformation was reported for the Cantor alloy after high-pressure torsion at Cryo-T (e.g., [36]) The starting microstructures of the three HEAs are shown in Figure 2 in the form of inverse pole figure (IPF) maps. All the HEAs (1 to 3) are fully recrystallized and have nearly equiaxed grains with a similar mean size of about 20 µm (twin boundaries (TBs) excluded).…”

“…Apart from that, twinning stabilizes the Bs component by relaxing certain constraints of polycrystal strain compatibility. This also reduces the intensity of Cu and S. For large CR reductions, shear banding leads to rotations of the Bs-type shear texture components to G and Bs [32,36]. This deformation instability can arise from planar slip induced by large dislocation dissociation, latent hardening caused by closely spaced twin lamellae, and short-range order (SRO).…”

Recent Advances in Additive Manufacturing of High Entropy Alloys and Their Nuclear and Wear-Resistant Applications

“…Zhang et al [128] reviewed high pressure induced phase transitions in HEAs. Application of high pressure torsion [37,[129][130][131][132][133][134][135][136][137][138][139][140][141][142] is more frequent than other pressure techniques [136,[143][144][145][146][147][148][149][150].…”

From diluted solid solutions to high entropy alloys: Saturation grain size and mechanical properties after high pressure torsion

“…has the highest hardness. In literature, higher dislocation densities after HPT deformation are found for the Cantor alloy (Ni20 in the order of 10 16 m -2 [22]), in comparison to pure Ni (Ni100 10 15 m -2 [23]). The higher dislocation density for Ni20 could also contribute to the increase in hardness from Ni100 to Ni20.…”