Compositional dependence of thermal and mechanical properties of quaternary Zr-Cu-Ni-Al bulk glassy alloys

To determine the optimized composition of quaternary Zr-Cu-Ni-Al bulk glassy alloy, its thermal and mechanical properties are examined. Zr shows high correlation coefficients with T g and Vickers hardness, whereas Ni and Al show high correlation coefficients with T l and T x , respectively. Only Cu shows no remarkable correlation coefficient with any thermal or mechanical properties. We conclude that a compositional region with a high (over 135 kJ/m 2 ) U-notch Charpy impact (CUE) value is located around the Zr 52 Cu 30 Ni 8 Al 10 bulk glassy alloy, which exhibits a maximum CUE of 165 kJ/m 2 . Moreover, a compositional region with high tensile strength (over 2000 MPa) is also located around the Zr 48 Cu 32 Ni 8 Al 12 bulk glassy alloy, which shows a maximum tensile strength of 2100 MPa

A Trial on Detecting Fluctuations in Bulk Metallic Glass Beams by Strain Contrast Variation Method-Use of High Energy Small-Angle Scattering

Heterogeneity in annealed Zr-Cu-Al alloys with high ductility has been examined by high-energy small-angle scattering with strain variation method. Although the statistics is still poor for detailed analysis, it was found that the heterogeneity in the sample showed clear enhancement by applied tensile strain, and the characteristic size of the heterogeneity was of the same order of magnitude as the one observed by high resolution electron microscopy. With surface insensitivity of the present method, anomalous small-angle scattering results at Cu K absorption edge for the same sample was briefly discussed

Elastic properties of Zr-based bulk metallic glasses studied\ud by resonant ultrasound spectroscopy

We report measurements of the elastic properties of Zr-based bulk metallic glasses,\ud Zr52.5Cu17.9Ni14.6Al10Ti5, Zr50Cu30Ni10Al10, and Zr50Cu40Al10 between 5 K and\ud 300 K. Both the shear and longitudinal modulus have been measured as a function of\ud temperature, allowing accurate determination of the Poisson’s ratio and the related\ud ratio of bulk modulus to shear modulus, K/G. These data make it possible to assess the\ud influence of the alloy’s composition on the mechanical properties and enable an\ud evaluation of the correlation between the elastic moduli and the ductility of the alloys

Elastic properties of Zr-based bulk metallic glasses studied by resonant ultrasound spectroscopy

We report measurements of the elastic properties of Zr-based bulk metallic glasses, Zr52.5Cu17.9Ni14.6Al10Ti5, Zr50Cu30Ni10Al10, and Zr50Cu40Al10 between 5 K and 300 K. Both the shear and longitudinal modulus have been measured as a function of temperature, allowing accurate determination of the Poisson’s ratio and the related ratio of bulk modulus to shear modulus, K/G. These data make it possible to assess the influence of the alloy’s composition on the mechanical properties and enable an evaluation of the correlation between the elastic moduli and the ductility of the alloys

マウスの神経細胞において、Ischemic postconditioningはmitochondrial permeability transition poreとKATPチャネルの開口を介してNMDA受容体電流を低下させる。

Ischemic postconditioning (PostC) is known to reduce cerebral ischemia/reperfusion (I/R) injury; however, whether the opening of mitochondrial ATP-dependent potassium (mito-KATP) channels and mitochondrial permeability transition pore (mPTP) cause the depolarization of the mitochondrial membrane that remains unknown. We examined the involvement of the mito-KATP channel and the mPTP in the PostC mechanism. Ischemic PostC consisted of three cycles of 15 s reperfusion and 15 s re-ischemia, and was started 30 s after the 7.5 min ischemic load. We recorded N-methyl-D-aspartate receptors (NMDAR)-mediated currents and measured cytosolic Ca²⁺ concentrations, and mitochondrial membrane potentials in mouse hippocampal pyramidal neurons. Both ischemic PostC and the application of a mito-KATP channel opener, diazoxide, reduced NMDAR-mediated currents, and suppressed cytosolic Ca2+ elevations during the early reperfusion period. An mPTP blocker, cyclosporine A, abolished the reducing effect of PostC on NMDAR currents. Furthermore, both ischemic PostC and the application of diazoxide potentiated the depolarization of the mitochondrial membrane potential. These results indicate that ischemic PostC suppresses Ca²⁺ influx into the cytoplasm by reducing NMDAR-mediated currents through mPTP opening. The present study suggests that depolarization of the mitochondrial membrane potential by opening of the mito-KATP channel is essential to the mechanism of PostC in neuroprotection against anoxic injury.博士（医学）・甲第781号・令和3年3月15日© Springer Science+Business Media, LLC, part of Springer Nature 2020This is a post-peer-review, pre-copyedit version of an article published in Cellular and molecular neurobiology. The final authenticated version is available online at: http://dx.doi.org/10.1007/s10571-020-00996-y

Ténacité et pré-fissuration par fatigue de verres métalliques massifs ZrCuAlNi : influence de l'oxygène

Une étude sur la ténacité de verres métalliques massifs ZrCuAlNi a été menée sur des échantillons, qui avec une très faible teneur en oxygène, qui avec une faible teneur en oxygène (contenant des défauts oxydes). On montre que la ténacité, au contraire des autres propriétés mécaniques, est fortement diminuée par la présence de ces défauts lors d'essais sur éprouvettes entaillées. Des essais de préfissuration par fatigue ont été menés sur des éprouvettes de flexion : si celles avec les verres contenant des dendrites ont été couronnées de succès, celles avec les verres complètement amorphes n'ont pas été concluantes du fait de l'apparition de fissures non perpendiculaires à la sollicitation. Il est supposé que cet état de fait est inhérent au matériau, ce qui ne s'observe pas habituellement du fait du caractère endommageant et guidant des défauts oxydes présents dans les échantillons étudiés dans la littérature

Tensile properties of Zr70Ni16Cu6Al8 BMG at room and cryogenic temperatures

The mechanical behaviour in tension of a hypoeutectic Zr70Ni16Cu6Al8 Bulk Metallic Glass (BMG) was studied at room (295 K) and cryogenic temperatures (150 K and 77 K) using various strain rates between 10−4 and 10−1 s−1. The yield strength was found to increase at lower temperatures with average values increasing by 16%, from 1503 MPa at 295 K to 1746 MPa at 77 K. The Zr-based BMG was found to exhibit tensile plastic elongation of about 0.4% before fracture at room temperature and high strain rates (10−1 s−1). Even higher tensile plasticity was recorded at low temperatures; plastic deformation was found highest at the intermediate temperature (150 K) reaching remarkable plastic strains in the order of 3.9%, while values up to 1.5% were recorded at 77 K. The lateral surface of the tensile specimens was observed in-situ during deformation using a high frame rate camera offering interesting insights with regard to the deformation mechanisms. Room temperature plasticity occurred through the formation and interaction of several nucleated shear bands before critical failure, while at intermediate and liquid nitrogen temperatures, most of the plastic deformation was accommodated through stable flow within a single shear band

Probing heat generation during tensile plastic deformation of a bulk metallic glass at cryogenic temperature

Despite significant research efforts, the deformation and failure mechanisms of metallic glasses remain not well understood. In the absence of periodic structure, these materials typically deform in highly localized, thin shear bands at ambient and low temperatures. This process usually leads to an abrupt fracture, hindering their wider use in structural applications. The dynamics and temperature effects on the formation and operation of those shear bands have been the focus of long-standing debate. Here, we use a new experimental approach based on localized boiling of liquid nitrogen by the heat generated in the shear bands to monitor the tensile plastic deformation of a bulk metallic glass submerged in a cryogenic bath. With the “nitrogen bubbles heat sensor”, we could capture the heat dissipation along the primary shear banding plane and follow the dynamics of the shear band operation. The observation of nitrogen boiling on the surface of the deforming metallic glass gives direct evidence of temperature increase in the shear bands, even at cryogenic temperatures. An acceleration in bubble nucleation towards the end of the apparent plastic deformation suggests a change from steady-state to runaway shear and premonitions the fracture, allowing us to resolve the sequence of deformation and failure events

Internal structures of a subaerial dacite cryptodome at Usu volcano, Hokkaido, Japan

A partly eroded, subaerial, dacite cryptodome at Showa-Shinzan, Usu volcano, Hokkaido, Japan, displays its internal structures, and provides an excellent opportunity to study contact relationship between cryptodome and overlying sediment. The margin of the cryptodome comprises two facies: inner coherent dacite and outer dacite breccia. The coherent dacite facies is ~5 m in the exposed section, and consists of homogeneous or weakly flow-banded, feldspar-phyric dacite. The dacite breccia facies envelope the coherent dacite facies, and is 4-5 m thick. The breccia is monomictic, non-stratified and consists of angular dacite clasts up to 15 cm across in a cogenetic matrix. The overlying sediment directly covers the dacite breccia facies, and comprises reddish-brown, fluvial deposit. The dacite breccia formed by　fracturing of coherent dacite in response to cooling contraction, and shearing of the fractured dacite due to movement of the growing cryptodome.特集 : 「2003年度実施の地域との共同研究の報告