题目：Development of Zr-Cu-Ni-Al Bulk Metallic Glasses with High Plastic Deformability and Application
报告人：Prof. Tohru Yamasaki，University of Hyogo, Japan
Zr55Cu30Ni5Al10(Zr55), Zr65Cu20Ni5Al10(Zr65) and Zr65+xCu17-xNi5Al10M3(Zr65+xM3, x = 0, 1.5 and 3 at.%, M= Au and Pd) bulk metallic glasses (BMGs) have been prepared by a tilt casting method. DSC results of the Zr65-BMG indicated the presence of a wide supercooled liquid region of 119 K between the glass transition temperature (Tg) of 644 K and the crystallization temperature (Tx) of 763 K. In contrast, by the Au/Pd addition BMGs, precipitation of an icosahedral quasicrystalline phase (I-phase) was observed in their supercooled liquid temperature regions. Compressive test was carried out at an initial strain rate of 5 x 10-4s-1at room temperature. By the Au/Pd additions, the yield stress was almost unchanged but the plastic strain at fracture was increased largely. The plastic strains at fracture of Zr55-, Zr65- and Zr65Au3/Pd3-BMGs were about 2 %, 10 % and more than 20 %, respectively. In the Zr66.5Au3/Pd3-BMGs, stress-increasing like a work hardening during plastic deformation was observed until more than 5% of compressive strain. By the transmission electron microscopy of the Au/Pd-addition BMGs, precipitation of nanocrystallites having about 5~10 nm in diameter was observed near the fractured surfaces of the compressive test specimens. So, the large increase of the plastic strain may be due to the work hardening by the dynamic precipitation of I-phase during plastic deformation. For industrial applications of Zr-based bulk metallic glasses with high yielding stress of about 1.5 GPa, nanoimprint moulding consisted of line and space structures with the interval of 700 nm and 300 nm was almost achieved successfully under the high moulding stress of about 2 GPa at room temperature.
题目：Tensile Plastic Deformation of Zr-based Bulk Metallic Glasses
报告人：Prof. Kazutaka Fujita, National Institute of Technology, Ube College, Japan
Tensile tests on monolithic Zr-based Bulk metallic glass with high viscosity about more than 108Pa･sec were carried out to investigate the plastic deformation properties.
As the result, a plastic strain of about 0.3% with work hardening and following plastic strain of about 0.7% with serrations and work softening were shown on the stress-strain curves. Many shear bands on the large surface area of parallel part of the specimen were observed on the photographs by SEM and images by in-situ high speed video camera. Number of serrations corresponded well with number of the large shear bands.
It is presumed that not softening but hardening and serrations are induced by increasing viscosity in the shear bands due to initiation and growth of the quasicrystal cores during the plastic deformation.