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Sasaki, T.T.,Hono, K.,Vierke, J.,Wollgarten, M.,Banhart, J. Elsevier Sequoia 2008 Materials science & engineering. properties, micro Vol.490 No.1
Amorphous Al<SUB>85</SUB>Ni<SUB>10</SUB>La<SUB>5</SUB> powders were consolidated to cylindrical samples by spark plasma sintering (SPS), and their microstructures and mechanical properties were investigated. When the powders were consolidated below the crystallization temperature, an amorphous phase was retained in the consolidated sample. Sintering above the crystallization temperature caused full crystallization. The Vickers hardness of the amorphous-containing sample was about 350HV in the as-sintered state and increased up to 450HV by a subsequent heat treatment just below the crystallization temperature. The highest hardness was achieved in a nanocrystalline microstructure. Compression tests revealed the brittle nature of the consolidated samples although the fracture and yield strength was higher than 1GPa. The brittleness is due to the low relative density of the amorphous-containing samples and the presence of a large amount of intermetallic compounds in the fully crystallized sample.
Effect of melt temperature on the mechanical properties of bulk metallic glasses
Kumar, Golden,Ohkubo, Tadakatsu,Hono, Kazuhiro Cambridge University Press (Materials Research Soc 2009 Journal of materials research Vol.24 No.7
<P>The effect of melt temperature on the structure and mechanical properties of three Zr-based bulk metallic glasses (BMGs)-Zr62Cu17Ni13Al8, Zr55Cu20Ni10Al10Ti5, and Zr52.5Cu17.9Ni14.6Al10Ti5 (Vit105)-has been studied. The results show that the BMGs cast from higher melt temperature exhibit large plastic strains despite their amorphous structure. The samples become macroscopically brittle when the quenched-in crystals form an interconnected microstructure. In contrast to previous studies, there is no notable effect on the Poisson’s ratio (ν) and other elastic constants.</P>
Structure of shear bands in Pd<sub>40</sub>Ni<sub>40</sub>P<sub>20</sub> bulk metallic glass
Chen, Y.M.,Ohkubo, T.,Mukai, T.,Hono, K. Cambridge University Press (Materials Research Soc 2009 Journal of materials research Vol.24 No.1
<P>The atomic structure of shear bands in Pd40Ni40P20 bulk metallic glass has been compared to an undeformed matrix phase using pair distribution functions (PDFs) derived from energy filtered nanobeam electron diffraction. Shear bands do not show any characteristic contrast in transmission electron microscopy (TEM) images when specimens are prepared with uniform thickness. PDFs from a shear band exhibit a slight decrease in the first peak, indicating a slight difference in packing density and short range order compared to the undeformed matrix.</P>
Bimodally grained high-strength Fe fabricated by mechanical alloying and spark plasma sintering
Srinivasarao, B.,Oh-ishi, K.,Ohkubo, T.,Hono, K. Elsevier Science 2009 Acta materialia Vol.57 No.11
Nanocrystalline iron containing a certain fraction of coarse grains with nanosized oxide dispersoids has been processed by mechanically milling Fe powder and subsequent spark plasma sintering. Sintered samples exhibited a high tensile strength of 2100MPa with 5% ductility; by optimizing the sintering conditions, it was possible to tune the strength-ductility balance. The optimally sintered material showed a tensile strength of 1500MPa and 15% elongation. The microstructure consists of nanograined (<100nm) as well as coarse-grained regions (>1μm) with uniform dispersion of nanosized chromium oxide particles (∼10nm). The strength and elongation show strong dependence on the volume fraction of the coarse grains, and the high strength can be attributed to the ultrafine grain size of the nanograined regions and precipitation hardening by the oxide dispersoids. The ductility is considered to be due to the presence of coarse grains.