High-entropy alloys (HEAs) comprise a novel class of scientifically and technologically interesting materials. Among these, equatomic CrMnFeCoNi with the face-centered cubic (FCC) structure is noteworthy because its ductility and strength increase with decreasing temperature while maintaining outstanding fracture toughness at cryogenic temperatures. Here we report for the first time by single-crystal micropillar compression that its bulk room temperature critical resolved shear stress (CRSS) is ~33–43 MPa, ~10 times higher than that of pure nickel. CRSS depends on pillar size with an inverse power-law scaling exponent of –0.63 independent of orientation. Planar ½   {111} dislocations dissociate into Shockley partials whose separations range from ~3.5–4.5 nm near the screw orientation to ~5–8 nm near the edge, yielding a stacking fault energy of 30 ± 5 mJ/m2. Dislocations are smoothly curved without any preferred line orientation indicating no significant anisotropy in mobilities of edge and screw segments. The shear-modulus-normalized CRSS of the HEA is not exceptionally high compared to those of certain concentrated binary FCC solid solutions. Its rough magnitude calculated using the Fleischer/Labusch models corresponds to that of a hypothetical binary with the elastic constants of our HEA, solute concentrations of 20–50 at.%, and atomic size misfit of ~4%.

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Size effect, critical resolved shear stress, stacking fault energy, and solid solution strengthening in the CrMnFeCoNi high-entropy alloy

Product miniaturization is an emerging trend for facilitating product usage, enabling unique product functions to be implemented in micro-scaled geometries and features, and further reducing product weight and volume. Recently, a demand for microparts increased significantly in many industry clusters. Development of the advanced micromanufacturing technologies for fabrication of such microparts has thus become a critical issue. Microforming, which offers attractive characteristics including high productivity, low cost and good quality of the formed parts, provides a promising approach to fabricating metallic microparts. In the last two decades, a lot of effort has been made to the researches on size effect related deformation behaviors in microforming process and the development of the process. Having a panorama of these researches is necessary to support micropart design and development via microforming, and further advance this micromanufacturing process. In this paper, an intensive review on the latest development of microforming technologies is presented. First of all, the paper is focused on the review of the size effect-affected deformation behaviors and the mechanisms of the changes of flow stress, flow behavior, fracture behavior, elastic recovery, tooling–workpiece interfacial friction and the surface finish of the formed parts. The state-of-the-art microforming processes, including micro deep drawing, microembossing, micropunching, microcoining, microextrusion, microheading, and micro progressive forming are then presented. Finally, some research issues from the implementation of mass production perspective are also discussed.

A review on the state-of-the-art microforming technologies

Geometry and grain size effects on the fracture behavior of sheet metal in micro-scale plastic deformation

We report the synthesis, mechanical properties, and deformation mechanisms of polycrystalline, platinum nanocylinders of grain size d = 12 nm. The number of grains across the diameter, D/d, was varied from 5 to 80 and 1.5 to 5 in the experiments and molecular dynamics simulations, respectively. An abrupt weakening is observed at a small D/d, while the strengths of large nanopillars are similar to bulk. This “smaller is weaker” trend is opposite to the “smaller is stronger” size effect in single crystalline nanostructures. The simulations demonstrate that the size-dependent behavior is associated with the distinct deformation mechanisms operative in interior versus surface grains.

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Size-Dependent Deformation of Nanocrystalline Pt Nanopillars

Microstructural size effects on mechanical properties of high purity nickel

Effect of specimen thickness on mechanical properties of polycrystalline aggregates with various grain sizes

Left-sided hemichorea developed suddenly in a 73-year-old male Computed tomography revealed a left subdural hematoma (SDH) and infarction in the right corona radiata and temporo-occipital region Hemichorea subsided completely after removal of the SDH Postoperative single photon emission computed tomography with technetium-99m-hexamethyl-propyleneamine oxime revealed a global low-perfusion area in the right cerebral hemisphere Right carotid angiography demonstrated severe stenosis of the trunk of the right middle cerebral artery The cerebral blood flow in the right cerebral hemisphere had probably already decreased to nearly the critical level and was reduced further by the left SDH, inducing the left-sided hemichorea due to dysfunction of the right cerebral hemisphere This case shows that when hemichorea ipsilateral to a SDH is present, it is important to ascertain whether there is a pre-existing ischemic lesion in the contralateral cerebral hemisphere, particularly in the basal ganglia, thalamus, or corona radiata

Hemichorea associated with ipsilateral chronic subdural hematoma--case report.

A 54-year-old female presented with apparent isolated hypothalamic histiocytosis X associated with diabetes insipidus and Korsakoff's syndrome. Computed tomographic and magnetic resonance imaging demonstrated a single hypothalamic mass. A craniotomy for biopsy found granulation tissue of unknown cause. Further investigation discovered genital bleeding before admission. Biopsy of the cervix uteri revealed histiocytosis X. Further studies showed the disease was restricted to the hypothalamus and the endometrium of the cervix uteri. Low-dose irradiation led to partial regression of the hypothalamic mass and improvement of Korsakoff's syndrome. Even when a diagnosis of isolated hypothalamic histiocytosis X is confirmed, the possibility of another histiocytosis X lesion in an unexpected region must be considered.

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Kenji Shibata

Papers

Effect of specimen thickness on mechanical properties of polycrystalline aggregates with various grain sizes

Hemichorea associated with ipsilateral chronic subdural hematoma--case report.

Hypothalamic histiocytosis X with diabetes insipidus and Korsakoff's syndrome--case report.