Crystallization during bending of a Pd-based metallic glass detected by x-ray microscopy.

Without the availability of slip systems and dislocation glide as in crystalline materials, metallic glasses resist irreversible deformation to elastic strains of 2% or more before undergoing heterogeneous plastic flow via the formation of shear bands. Observation of crystallite formation under compressive load was previously obtained by transmission electron microscopy. In this Letter, we present results of nondestructive x-ray diffraction microprofiling of the section of a bent glassy Pd40Cu30Ni10P20 ribbon in transmission using a synchrotron microbeam. Crystallization was clearly detected but only on the compression side of the neutral fiber. The experimental results and crystal nucleation frequency analysis are consistent with massive nucleation in shear bands forming under compressive stress but mainly for metallic glasses that show a large supercooled liquid temperature range ΔT=T(x)-T(g) between glass transition at T(g) and crystallization at T(x). The phenomenon is sensitively dependent on the volume change that accompanies crystallization in the supercooled liquid temperature range where the much larger liquid-state thermal expansion coefficient significantly increases the specific volume difference between the liquid and crystalline states. The results are also consistent with the many reports of extensive strain to fracture of metallic glasses under compressive load but not under tension.

Fabrication and nano-imprintabilities of Zr-, Pd- and Cu-based glassy alloy thin films.

With the aim of investigating nano-imprintability of glassy alloys in a film form, Zr(49)Al(11)Ni(8)Cu(32), Pd(39)Cu(29)Ni(13)P(19) and Cu(38)Zr(47)Al(9)Ag(6) glassy alloy thin films were fabricated on Si substrate by a magnetron sputtering method. These films exhibit a very smooth surface, a distinct glass transition phenomenon and a large supercooled liquid region of about 80 K, which are suitable for imprinting materials. Moreover, thermal nano-imprintability of these obtained films is demonstrated by using a dot array mold with a dot diameter of 90 nm. Surface observations revealed that periodic nano-hole arrays with a hole diameter of 90 nm were successfully imprinted on the surface of these films. Among them, Pd-based glassy alloy thin film indicated more precise pattern imprintability, namely, flatter residual surface plane and sharper hole edge. It is said that these glassy alloy thin films, especially Pd-based glassy alloy thin film, are one of the promising materials for fabricating micro-machines and nano-devices by thermal imprinting.