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In this study, mechanical tests were conducted on a face-centered cubic FeCoNiCrMn high-entropy alloy, both in tension and compression, in a wide range of strain rates (10−4–104 s−1) ...to systematically investigate its dynamic response and underlying deformation mechanism. Materials with different grain sizes were tested to understand the effect of grain size, thus grain boundary volume, on the mechanical properties. Microstructures of various samples both before and after deformation were examined using electron backscatter diffraction and transmission electron microscopy. The dislocation structure as well as deformation-induced twins were analyzed and correlated with the measured mechanical properties. Plastic stability during tension of the current high-entropy alloy (HEA), in particular, at dynamic strain rates, was discussed in lights of strain-rate sensitivity and work hardening rate. It was found that, under dynamic conditions, the strength and uniform ductility increased simultaneously as a result of the massive formation of deformation twins. Specifically, an ultimate tensile strength of 734 MPa and uniform elongation of ∼63% are obtained at 2.3 × 103 s−1, indicating that the alloy has great potential for energy absorption upon impact loading.
This study was designed to examine osteoconductive effects of Mg in rats tibia. The animals were sacrificed after 1, 2, and 8 weeks. The elemental analysis was performed using SEM/EDX at week 1. ...Following X-ray micrography at weeks 2 and 8, samples were embedded in paraffin. The expression of osteocalcin was observed by immunohistochemical staining. The element concentrations of fibrous capsules around the specimens were also measured by ICP-MS. The concentrations of Ca and P on the surface of the Mg specimen increased in SEM/EDX. The tissue specimen showed new bone formation on the bone surface near the implanted area. The concentrations of Mg, Ca, and P were high in the fibrous capsules surrounding Mg. Implantation induced differentiation of osteoblasts, and this process was considered to be associated with new bone formation. Induction of cell differentiation may be influenced by corrosion products in addition to corroding magnesium.
•ECAE processing was applied to a Mg–Ca alloy that is a potential biomaterial.•The aim was to explore increasing the strength while retaining the damping capacity.•The texture and local ...misorientation distribution depended on the ECAE temperature.•The alloy processed by ECAE showed a high yield strength without sacrificing the damping capacity.
Equal channel angular extrusion (ECAE) was applied to an extruded Mg–1.0mass%Ca alloy to achieve a high strength and high damping capacity. Microstructure observations revealed that the texture and local misorientation distribution depend on the ECAE temperature. ECAE at a low temperature of 260°C resulted in a high average Schmid factor of basal slip and a high kernel average misorientation in the processed alloy. Consequently, the alloy processed by ECAE showed a high yield strength without sacrificing the damping capacity.
The effect of grain boundary structures on the deformation behavior at the grain boundaries in magnesium was examined by the nanoindentation creep test. The results of the nanoindentation creep test ...showed that the dominant deformation mechanism around the grain boundary was grain boundary sliding; however, the occurrence of grain boundary sliding was closely related to the grain boundary energy. The grain boundary with high energy showed high strain rate sensitivity, which was the same tendency as that of the other metallic materials. Furthermore, the addition of aluminum atoms into magnesium tended to prevent the grain boundary sliding due to the decrease in grain boundary energy.
► The grain boundary structures in Mg affected the deformation mechanism. ► The grain boundary with high energy indicated high strain rate sensitivity. ► The addition of Al atoms into Mg decreased the grain boundary energy. ► Mg–Al alloy prevented the grain boundary sliding to compared that with Mg.
The present study was designed to investigate the biodegradation behavior of Mg alloy plates in the maxillofacial region. For in vitro analysis, the plates were immersed in saline solution and ...simulated body fluid. For in vivo, the plates were implanted into the tibia, head, back, abdominal cavity, and femur and assessed at 1, 2, and 4 weeks after implantation. After implantation, the plate volumes and the formed insoluble salt were measured via micro-computed tomography. SEM/EDX analysis of the insoluble salt and histological analysis of the surrounding tissues were performed. The volume loss of plates in the in vitro groups was higher than that in the in vivo groups. The volume loss was fastest in the abdomen, followed by the head, back, tibia, and femur. There were no statistically significant differences in the insoluble salt volume of the all implanted sites. The corrosion of the Mg alloy will be affected to the surrounding tissue responses. The material for the plate should be selected based on the characteristic that Mg alloys are decomposed relatively easily in the maxillofacial region.
The fracture toughness of extruded pure magnesium increased with grain refinement due to the effect of the plastic zone, which is a sensitive factor related to the mechanical properties of yield ...strength, elongation-to-failure and strain hardening exponent.
An equiatomic high entropy CoCrFeMnNi alloy has been processed by caliber rolling and its microstructure studied by transmission electron microscopy (TEM). The cast dendritic structure and ...compositional inhomogeneity was reduced to a nanoscale microstructure. Domains as thin as 50 nm elongated in the rolling direction were formed after 19 rolling passes. Boundaries on {111} plane perpendicular to the rolling direction were also observed. FCC twins were observed in the cross-section of the rolled rods, about 50 nm in thickness. A stack of twins and other planar faults result in a periodicity of three times the interplanar spacing of the {111} twinning plane to about 6.2 Å. Lattice imaging shows interference fringes and diffraction effects which can be attributed to domain formation at a very fine scale. These give rise to diffraction streaks and additional spots. Extra diffraction spots and associated diffuse intensity also point to an underlying lattice not fully ordered. The nanoscale domain boundaries are often on {111} planes which are not simple stacking faults but complex in structure.
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•Microstructure of cast CoCrFeMnNi high entropy alloy processed by caliber rolling•Cast structure and chemical inhomogeneity was reduced to nano-scale•Domains of 50 nm thickness elongated directionally along the rolling direction•Profuse nano-twins and nano-domains of {111} plane stacking boundaries•Interference of two overlapping lattices, one only partially ordered
Differential speed rolling (DSR) was applied to the AZ31 magnesium alloy, intended to modify the texture and thus to enhance the room temperature ductility. Especially, effect of DSR temperature on ...resulting room temperature tensile properties and texture was investigated at a fixed rolling speed ratio of 1.1. The strength was not affected by the rolling temperature: the yield strength and the ultimate tensile strength for all materials processed by DSR were approximately 240 and 290
MPa, respectively. On the other hand, elongation-to-failure increased from 13.6 to 18.5% with decreasing rolling temperature from 573 to 473
K. In addition, the material processed by DSR exhibited approximately 1.5 times larger ductility than that by conventional symmetric rolling at a rolling temperature of 473
K. The DSR at 523 and 473
K resulted in the basal plane orientation at the position inclined by ∼5 and 8° from the normal direction toward the rolling direction, respectively. It was suggested that the higher ductility of the material processed at lower temperatures is attributed to the slight change in the basal plane orientation and/or reduction in grain size.
Fine and coarse grained (5–20 μm) and ultra-fine-grained (down to 1 μm) samples of a binary Mg-Al alloy were fabricated by extrusion at various temperatures. When tested in compression, a slight ...stress drop was observed after yielding, followed by a plateau in flow stress. This behavior is typical of textured fine-grained samples. Examination of deformed structures within the ultra-fine-grained samples at various levels of deformation showed that the stress drop after yielding is due to an occurrence of long, thin twins across low angle boundaries and in unrecrystallized regions. In the plateau region, extensive twinning occurs inside individual grains. Then, in a rapid strain hardening region that follows the plateau region, stress concentrations were found to build up on boundaries. Such pile-ups could be responsible for a lowering of fracture strain.
•Compression deformation of an ultra fine grained Mg-Al alloy has been studied.•Yielding occurs by formation of long twins in unrecrystallized regions.•Limited number of twins in each grain gives rise to a plateau in the flow curve.•Refining grain size to ∼1 μm leads to activation of non-basal slips.•Intense activity of non-basal slip results in strain hardening beyond 6% strain.
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