Wenqian Wu

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

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.

Effects of torsional deformation on the microstructures and mechanical properties of a CoCrFeNiMo0.15 high-entropy alloy

Abstract The effects of torsional deformation on the microstructures and mechanical properties of a CoCrFeNiMo0.15 high-entropy alloy have been investigated. The torsional deformation generates a gradient microstructure distribution due to the gradient torsional strain. Both dislocation activity and deformation twinning dominated the torsional deformation process. With increasing the torsional equivalent strain, the microstructural evolution can be described as follows: (1) formation of pile-up dislocations parallel to the trace of {1 1 1}-type slip planes; (2) formation of Taylor lattices; (3) formation of highly dense dislocation walls; (3) formation of microbands and deformation twins. The extremely high deformation strain (strained to fracture) results in the activation of wavy slip. The tensile strength is very sensitive to the torsional deformation, and increases significantly with increasing the torsional angle.

Effects of annealing on the microstructural evolution and phase transition in an AlCrCuFeNi2 high-entropy alloy

An AlCrCuFeNi2 high entropy alloy (HEA) was prepared by arc melting, followed by annealing at different temperatures. The elemental distributions, phase formation, morphology and microstructural evolution of the HEA in both the as-cast state and annealed state were investigated. The results indicate that the HEA undergoes elements segregation, precipitation and spinodal decomposition. The as-cast alloy consists of Cr-Fe-Ni rich FCC dendritic (DR) phase and BCC interdendritic (ID) phase. Spherical Fe-Cr rich BCC precipitates were found to disperse in Al-Ni rich B2 (ordered BCC) matrix. After heat treatments, the distribution of elements clearly changes, along with changes of the constituent phase and morphology. After annealing at 600°C, the DR region remains Cr-Fe-Ni rich phase, while some spherical precipitates transform into the needle-like structure within the ID region. The L12 (ordered FCC) nanorod-shaped phase ((Ni,Cu)3Al) and plate-like Al-Ni rich phase form within the DR region when annealing up to 900°C. The L12 phase almost dissolves in the FCC matrix due to the order-disorder transition and an obvious coarsening of the Fe-Cr rich phase occurs after annealing at 1100°C. The segregation of Cu atoms at the interface between DR and ID regions is found at the as-cast state, while a uniform distribution of Cu atoms in DR and ID regions was observed after annealing at 1100°C.