Kyoto University · Engineering
Professor Shuhei Yoshida's research lab specializes in materials science and biomedicine, focusing on the development and characterization of advanced metallic alloys—particularly high and medium entropy alloys—with an emphasis on composition-structure-property relationships. The lab investigates mechanical behavior, dislocation dynamics, and thermal transport properties in complex concentrated alloys and refractory metals, utilizing advanced experimental and theoretical techniques. Additionally, the lab explores neurological disorders, particularly juvenile ischemic strokes and hypoxia-induced neuronal dysfunction, bridging materials science with clinical neurology.
Figures are computed from collected data and may differ slightly.
Non-equiatomic high entropy alloys (HEAs) and medium entropy alloys (MEAs) are expected to have the potential to exhibit good mechanical properties due to abundant composition designs compared to equiatomic alloys. It has been reported that an equiatomic CoCrNi MEA shows better strength-ductility balance than CoCrFeMnNi HEA, and there is a possibility that the mechanical properties can be further improved by changing chemical composition. Among the constituent elements, cobalt (Co) has the effec
The present work reports characteristics of dislocation slip behavior in an equi-atomic HfNbTiZr refractory medium entropy alloy (RMEA) and its systematic comparison with pure niobium (Nb). Fully-recrystallized specimens were fabricated by cold rolling and subsequent annealing, and uniaxial tensile deformation was applied at room temperature. Slip trace morphologies on the surfaces of the tensile-deformed materials were quantitatively characterized, and the so-called ψ and χ relationships of the
The thermal transport properties of random network, single-walled carbon nanotube (SWNT) films were assessed using Raman spectroscopy. Two types of SWNT films were investigated: single-layer and stacked. The single-layer films were fabricated by aerosol chemical vapour deposition and subsequent direct dry deposition, while the stacked films were prepared by placing the single-layer films on top of one another. The anisotropy of the network structures of each of these films was evaluated based on
Shear viscosity of molecular liquids is formulated and calculated with use of a time-dependent density-functional theory. Allowing for nonrigidity of each molecule, we obtain shear-induced distortion of both intramolecular and intermolecular correlations self-consistently, which makes it possible to calculate the shear viscosity. As a by-product we derive and solve a hypernetted-chain closure for equilibrium correlations in deformable molecular liquids. \textcopyright{} 1996 The American Physica
We have encountered 38 cases of juvenile ischemic strokes during the past 10 years, which included 16 cases of moyamoya disease and 22 cases of non-moyamoya strokes. The etiology could not be determined in most non-moyamoya strokes, except in 4 cases of cardiogenic embolism and 1 case of post-meningitic stroke. We further examined 13 cases of idiopathic strokes, which showed clinical symptoms of so-called acute infantile hemiplegia. Nine out of 13 patients developed strokes between 6 months and
Electrophysiologic studies were performed to examine the effects of hypoxia on neuronal activities of the lateral vestibular and spinal trigeminal nuclei using rats anesthetized with chloral hydrate. The rats inhaled a gas mixture of 5% oxygen and 95% nitrogen for 3.5 minutes to induce hypoxia, followed by room air. Under these conditions, mean PaO2 was decreased from 85 to 22 mm Hg 3 minutes after the start of the inhalation concomitant with a decrease in blood pressure from 108 to 55 mm Hg. Th
This study clarified the grain size dependence of the deformation microstructure evolution and work-hardening behavior in CoCrNi medium entropy alloy. We fabricated fully recrystallized specimens with coarse-grained (CG) and ultrafine-grained (UFG) specimens by severe plastic deformation and subsequent annealing processes. Tensile deformation was applied to the specimens at room temperature. The UFG specimen exhibited both high strength and high ductility compared to conventional UFG metals due
• Characteristics of recrystallization in FCC high entropy alloys (HEAs) were studied. • High-pressure torsion on HEAs resulted in nanocrystalline microstructures. • Significantly fine recrystallized microstructures were obtained after annealing. • Grain growth kinetics of HEAs were found to be much slower than pure FCC metals. • Slow grain growth can be due to solute drag enhanced by severe lattice distortion. Face-centered cubic (FCC) high- and medium-entropy alloys (HEAs/MEAs) develop fully r
Abstract In this study we report the deformation microstructures and strength of medium entropy alloys (MEAs) and high entropy alloys (HEAs), which are defined as alloys composed of four or less, and five or more principal elements, respectively, with (near-) equi-atomic concentrations. The friction stress (fundamental resistance to dislocation motion in the crystal lattice) and Hall-Petch relationship of various MEAs (CoCrFeNi, CoCrNi, etc.), taken as subsystems of the equi-atomic CoCrFeMnNi HE
Abstract This study revealed characteristics of the deformation behavior in high/medium entropy alloys (HEAs/MEAs) with face-centered cubic (FCC) structure. A Co 60 Ni 40 alloy and a Co 20 Cr 40 Ni 40 MEA having low and high friction stresses (fundamental resistance to dislocation glide in solid solutions), respectively, but similar in other properties, including their stacking fault energy and grain sizes, were compared. The MEA exhibited a higher yield strength and work-hardening ability than
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