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In the present work, the mechanical properties of a newly developed metastable 65Fe-15Ni-8Co-8Mn-3Ti-Si (at%) ferrous medium-entropy alloy were investigated at 298 K and 77 K. The short-time annealing followed by aging treatment is employed to gain heterogeneous microstructure containing fine- and coarse-grains decorated with nanometric precipitates. The yield strength of the alloy enhances substantially from 0.9 GPa at 298 K and 1.3 GPa at 77 K in the annealed state, respectively, to 1.1 GPa and 1.5 GPa after the aging treatment, while the total elongation sustains more than 20%. This extraordinary improvement results from the synergistic effect of hetero-deformation-induced strengthening, mechanical nano-twins, and martensitic phase transformation along with precipitation strengthening of the well-distributed nano-scale Fe2SiTi and Ni3Ti precipitates during tensile deformation of the aged alloy. Therefore, the corresponding ferrous MEA can be considered as a promising candidate for ultra-high-strength components at extreme service conditions.

A strategy to improve the tensile properties of Co17.5Cr12.5Fe55Ni10Mo5 (at%) medium-entropy alloy through high-pressure torsion and subsequent annealing is presented in this work. Microstructural study revealed that the high-pressure torsion process led to the formation of fine grains (≤~1 μm) and profuse nano-scale Mo-rich μ-phase precipitates. And resultantly, the yield strength of the alloy was tuned from ~400 MPa to ~1 GPa, while preserving reasonable uniform elongation over 15%. The combination of strengthening from grain refinement and precipitation contributed to the excellent strength, while the post-HPT annealing provided substantial ductility.

In this work, a high-entropy alloy of equiatomic CrMnFeCoNi was processed by vacuum induction melting followed by rolling. After cold rolling, annealing for one hour was conducted during which the annealing temperature was varied from 650 to 1000 °C. This was done to investigate the effect of microstructure on tensile properties and stretch formability (defined as the capability of materials to undergo plastic deformation under biaxial stretching). The strengthening effect of partial recrystallization, with a remaining small fraction of sigma phase particles, led to improved yield and tensile strengths while minimizing the loss of ductility. Fully recrystallized microstructure resulted in a slight increase in ductility, and a considerable decrease in strength, during a tensile test. On the other hand, the results for stretch formability suggest that partial recrystallization had exactly the opposite results. In this regard, the present results raise a new issue to consider when utilizing partial recrystallization for improvement of mechanical properties.

Herein, the deep drawability and deep drawing behavior of an equiatomic CoCrFeMnNi HEA and its microstructure and texture evolution are first studied for future applications. The CoCrFeMnNi HEA is successfully drawn to a limit drawing ratio (LDR) of 2.14, while the planar anisotropy of the drawn cup specimen is negligible. The moderate combination of strain hardening exponent and strain rate sensitivity and the formation of deformation twins in the edge region play important roles in successful deep drawing. In the meanwhile, the texture evolution of CoCrFeMnNi HEA has similarities with conventional fcc metals.

In the present work, the deformation mechanisms of the CoCrFeMnNi high-entropy alloy at 77 K were investigated using thermal activation analyses. The strain rate jump test was performed to estimate strain rate sensitivity and the activation volume of the alloy. Transmission electron microscopy analyses were performed to identify the evolution of twins at low temperatures. The insensitivity of activation volume to strain observed in the CoCrFeMnNi alloy at 77 K was different from the observed increase in the activation volume with strain at room temperature, which occurred due to the shearing of nanoscale inhomogeneities, such as co-clusters and short-range orders.

CoCrFeMnNi high-entropy alloys containing 1 at% carbon (C-HEAs) were additively manufactured using selective laser melting (SLM). Superior tensile properties of the as-built C-HEA (to previously reported ones) were achieved by utilizing multiple strengthening mechanisms (i.e. solid solution, grain refinement, dislocation density, and nano-precipitation) by this new manufacturing method. In particular, the SLM process could allow to maximize the strengthening effect of carbon addition to HEAs via finely distributed nano-carbides at the boundaries of solidification cellular structure. This work will open a new window to utilize the SLM process for enhanced mechanical properties of HEAs with great potential. CoCrFeMnNi high-entropy alloys containing 1 at% carbon were successfully produced by selective laser melting, and the alloys exhibited much better tensile performance than additive manufactured high-entropy alloy previously reported.

International audience; The contribution of kinematic hardening to the overall strain hardening of a high entropy alloy (HEA) was investigated for the first time ever. It was assessed for a single-phase equiatomic CoCrFeMnNi alloy based on a study of the Bauschinger effect. The observed occurrence of high back stresses signifies substantial kinematic hardening. We attribute it to the low probability of cross-slip in this HEA which, however, rises in the process of straining. A model that captures the mentioned effects was proposed and validated.

Deformation-induced twinning has been a notable example of overcoming the strength/ductility trade-off dilemma as a strengthening mechanism. By borrowing this concept from the area of TWIP steels, we designed a thermomechanical treatment for a CoCrFeMnNi high-entropy alloy to improve its mechanical characteristics. We used pre-straining at 77 K to introduce deformation-induced twins in the microstructure of the alloy, and then recovered it by annealing at 773 K, while avoiding recrystallization. The deformation-induced twins generated by pre-straining at 77 K were retained after this heat treatment, whilst partial recovery of dislocations occurred. As a result, the room-temperature mechanical properties of the alloy, including its strain hardening ability, were improved substantially.

New AlxCo50−xCu50−xMnx (x = 2.5, 10, and 15 atomic %, at%) immiscible medium-entropy alloys (IMMEAs) were designed based on the cobalt-copper binary system. Aluminum, a strong B2 phase former, was added to enhance yield strength and ultimate tensile strength, while manganese was added for additional solid solution strengthening. In this work, the microstructural evolution and mechanical properties of the designed Al-Co-Cu-Mn system are examined. The alloys exhibit phase separation into dual face-centered cubic (FCC) phases due to the miscibility gap of the cobalt-copper binary system with the formation of CoAl-rich B2 phases. The hard B2 phases significantly contribute to the strength of the alloys, whereas the dual FCC phases contribute to elongation mitigating brittle fracture. Consequently, analysis of the Al-Co-Cu-Mn B2-strengthened IMMEAs suggest that the new alloy design methodology results in a good combination of strength and ductility.

The nature of obstacles to dislocation motion in CoCrFeMnNi alloy was analyzed using the thermally activated deformation analyses at low temperatures. The strong temperature dependence of yield stress and small activation volume in CoCrFeMnNi favor the dislocation glide over the obstacles with high friction stress. The activation volume of CoCrFeMnNi alloy (10–100 b3) in this study is much smaller than those of conventional FCC metals (102~103 b3), but close to those observed in BCC metals (8–100 b3) and HCP metals (5–100 b3). The increase of the activation volume with strain supports overcoming the nanoscale inhomogeneity such as co-clusters and/or short range orders as the rate controlling mechanism. The transition of dislocation structure from planar array to cell structure at 20% strain in CoCrFeMnNi reported in the literature can be attributed to the prevalent shearing of nanoscale inhomogeneity with strain.

In this study, we achieved hetero-structuring of multi-phase (CuFe)100-xMnx (x = 15, 20, and 33 at%) medium-entropy alloys having excellent strength-ductility synergy by systematic investigation of microstructural and mechanical responses. The significant hetero-deformation-induced strengthening of the alloys is attributed to the high plastic incompatibility between Cu-rich and Fe-rich phases from thermally- and deformation-induced martensitic phase transformation.

A deformation-induced phase transformation in a face-centered cubic (FCC) Co 20 Cr 26 Fe 20 Mn 20 Ni 14 high-entropy alloy during cryogenic high-pressure torsion (HPT) discovered in this work is reported. Thermodynamic calculations prove that in the Co 20 Cr 26 Fe 20 Mn 20 Ni 14 alloy, a hexagonal close-packed (HCP) phase is stable at low temperatures. Microstructural and compositional analyses suggest that a diffusionless deformation-induced FCC-to-HCP phase transformation occurred during cryogenic HPT.

A thermodynamic description of the Al–Cu–Fe–Mn quaternary system has been developed for the design of high-strength immiscible dual-phase medium-entropy alloys. A new thermodynamic assessment for the Al–Cu–Mn ternary sub-system is performed, covering the entire composition range. Thermodynamic parameters of B2 and AlCuFe_τ and φ phases in the Al–Cu–Fe ternary sub-system are also revised based on a previous description that used different constituent binary descriptions. The reliability of the developed thermodynamic description for the Al–Cu–Fe–Mn quaternary system is experimentally confirmed by designing, fabricating, and analysing the phase structures of Al–Cu–Fe–Mn medium-entropy alloys.

In this work, the mechanical characteristics of high-entropy alloy Co20Cr26Fe20Mn20Ni14 with low-stacking fault energy processed by cryogenic and room temperature high-pressure torsion (HPT) were studied. X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses were performed to identify the phase and microstructure variation and the mechanical properties characterized by Vickers hardness measurements and tensile testing. Cryogenic HPT was found to result in a lower mechanical strength of alloy Co20Cr26Fe20Mn20Ni14 than room temperature HPT. Microstructure analysis by SEM and TEM was conducted to shed light on the microstructural changes in the alloy Co20Cr26Fe20Mn20Ni14 caused by HPT processing. Electron microscopy data provided evidence of a deformation-induced phase transformation in the alloy processed by cryogenic HPT. Unusual softening phenomena induced by cryogenic HPT were characterized by analyzing the dislocation density as determined from X-Ray diffraction peak broadening.

The enhancement of strength in materials by conventional strengthening mechanism is always accompanied by loss of ductility due to the reduced strain hardenability, leading to a strength–ductility trade-off. In this paper, we engineered Al0.3CoCrNi medium-entropy alloy to contain multi-phase hierarchical microstructure and demonstrated a high yield strength of ∼1 GPa, a high tensile strength of ∼1.2 GPa, with a uniform elongation and total elongation of ∼28% and ∼39%, respectively. The multi-phase hierarchical microstructure is developed by a simple processing route of cold rolling followed by annealing. The superior combination of strength and ductility is primarily attributed to the generation of back stress, high strain hardening rate, and formation of deformation twins.

We engineered an Al0.3CoCrNi medium-entropy alloy with heterogeneous grain structure and nanoscale precipitation through thermo-mechanical processing route, with an aim to achieve a remarkable combination of cryogenic yield strength and ductility. The alloy exhibited an exceptional combination of high cryogenic yield strength of ∼1.1 GPa and high uniform elongation of ∼37%.

In this study, the superplasticity of nanostructured V10Cr15Mn5Fe35Co10Ni25 (at%) high-entropy alloy processed by high-pressure torsion was investigated using high-temperature tensile testing in the temperature range of 873–1073 K and strain rate range of 5.0✕10−4 to 1.0✕10−2 s−1. The alloy exhibited extreme elongation at these elevated temperatures, with the greatest elongation of 770% at 973 K without any necking or a notable cavity in the fracture area. Other impressive achievements were also recorded (700% elongation at 1073 K and 3.3✕10−3 s−1 and 600% elongation under other conditions). The equiaxed microstructure was maintained in both the deformed and undeformed regions of the tensile specimen, demonstrating that grain-boundary sliding is the dominant mechanism of superplasticity.

A constitutive model based on the dislocation glide and deformation twinning is adapted to face-centered cubic high-entropy alloys (HEAs) as exemplified by the CrMnFeCoNi system. In this model, the total dislocation density is considered as the only internal variable, while the evolution equation describing its variation during plastic deformation is governed by the volume fraction of twinned material. The suitability of the model for describing the strain hardening behavior of HEAs was verified experimentally through compression tests on alloy CrMnFeCoNi and its microstructure characterization by electron backscatter diffraction and X-ray diffraction using synchrotron radiation. [GRAPHICS] . IMPACT STATEMENT We adopted a constitutive model based on dislocation density and twin volume fraction evolution, to analyze the deformation behavior of the high-entropy alloy CrMnFeCoNi theoretically.

Ultrafine-grained (UFG) Ti for improved mechanical performance as well as its surface modification enhancing biofunctions has attracted much attention in medical industries. Most of the studies on the surface etching of metallic biomaterials have focused on surface topography and wettability but not crystallographic orientation, i.e., texture, which influences the chemical as well as the physical properties. In this paper, the influences of texture and grain size on roughness, wettability, and pre-osteoblast cell response were investigated in vitro after HF etching treatment. The surface characteristics and cell behaviors of ultrafine, fine, and coarse-grained Ti were examined after the HF etching. The surface roughness during the etching treatment was significantly increased as the orientation angle from the basal pole was increased. The cell adhesion tendency of the rough surface was promoted. The UFG Ti substrate exhibited a higher texture energy state, rougher surface, enhanced hydrophilic wettability, and better cell adhesion and proliferation behaviors after etching than those of the coarse- and fine-grained Ti substrates. These results provide a new route for enhancing both mechanical and biological performances using etching after grain refinement of Ti.

Objective Chronic subdural hematoma (CSDH) is a common form of extra axial hemorrhage in the elderly. A surgical procedures such as a burr hole trephination are used for the CSDH treatment. The recurrence rate of CSDH is reported to range from 2.3 to 33%. In the current study, we focused on the determination of risk factors associated with the recurrence of CSDH. Methods We retrospectively reviewed 368 consecutive patients with CSDH treated by burr hole trephination. Univariate and multivariate analysis were performed to describe the relationships between clinical and radiological factors as well as the recurrence of CSDH. Results Totally 31 (8.4%) patients experienced a recurrence of CSDH in our study. The male group (10.2%) had a higher recurrence rate than the female group (3.1%). Also patients with malignant neoplasm history showed a high recurrence rate (17.9%). The recurrence rate of single layer CSDH (13.1%) and isodensity CSDH (11.7%) was highly significant also. Conclusion Sex, history of malignant neoplasm and the hematoma type on computed tomography were factors related with the recurrence of CSDH in our study. These findings may be supportive in the identification of patients at risk for a recurrence of CSDH.