Showing papers by "Mingwei Chen published in 2000"
TL;DR: An icosahedral (I) quasicrystalline phase with a grain size below 40 nm was formed as a metastable phase in crystallization of the bulk glassy Zr65Al7.5Cu17.5Mx alloys as mentioned in this paper.
Abstract: An icosahedral (I) quasicrystalline phase with a grain size below 40 nm was formed as a metastable phase in crystallization of the bulk glassy Zr65Al7.5Cu17.5−xNi10Mx (M=Ag, Pd, Au, or Pt; x=5 and 10 at %) alloys. The volume fraction (Vf) of the I phase is about 85% for the 5% M alloy and nearly 100% for the 10% M alloy. The I phase changes to Zr2Cu+Zr2Ni+Zr2Al3 in a fully annealed state. Compressive fracture strength (σc,f) and fracture elongation (ec,f) of the 10% Pd cylinder with a diameter of 2 mm are respectively 1640 MPa and 2.2% for the glassy phase and increase to 1830 MPa and 3.1% for the I phase. The increase in σc,f is due to the suppression effect of the I particles against the shear deformation of the intergranular glassy phase, and the increase in ec,f results from the localization effect of deformation into the glassy layer. The precipitation of the I phase implies that the glassy alloys include randomly oriented I configurations. The present work shows promise for the new class of high-strength nanoquasicrystalline materials.
73 citations
TL;DR: In this paper, the transformation and grain growth behavior of an icosahedral phase from the supercooled liquid region of rapidly quenched Zr 65 Cu 7.5 Al7.5 Ni 10 Ag 10 metallic glass have been examined by transmission electron microscopy.
Abstract: The transformation and grain growth behaviour of an icosahedral phase from the supercooled liquid region of rapidly quenched Zr 65 Cu 7.5 Al 7.5 Ni 10 Ag 10 metallic glass have been examined by transmission electron microscopy. The precipitation of the icosahedral phase proceeds according to a polymorphic reaction without any concentration change. The grain size increases linearly with an increase in annealing time and the growth rate strongly depends on the temperature. An Arrhenius plot of the logarithm of growth rate versus the reciprocal of annealing temperature yields a linear relationship, from which an activation energy for grain growth of 409 kJ mol -1 is obtained. This activation energy is much higher than those in the Al-Cu-V and Al-Mn-Si systems. This activation energy is attributed to the strong bonding among constitutional elements and the necessity of the rearrangement of atoms on a long length scale for grain growth. The kinetic data suggest that the icosahedral phase is stabilized by the difficulty of rearrangement of atoms.
32 citations
TL;DR: In this paper, the deformation of thin metallic films on Si substrates induced by thermal cycling was measured by employing an atomic force microscope, and the change in the size and shape of the thin films were determined.
Abstract: A method is proposed to measure the plastic deformation of thin metallic films on Si substrates induced by thermal cycling. The cross-sectional profiles of pattern-grown square Al films with a thickness of ∼250 nm and a size of ∼6 μm×6 μm were measured before and after thermal cycling by employing an atomic force microscope. With the assistance of statistical analysis, the change in the size and shape of the thin films were determined. Based on theoretical considerations, the thermal cycling deformation of thin films is attributed to creep and plasticity effects, accommodated by diffusion-controlled interfacial sliding.
26 citations
TL;DR: In this article, the formation and thermal stability of an icosahedral quasicrystalline phase in an annealed Zr65Al7.5Ni10Cu12.5Ag5 metallic glass have been investigated by X-ray diffraction and transmission electron microscopy analyses.
Abstract: The formation and thermal stability of an icosahedral quasicrystalline phase in an annealed Zr65Al7.5Ni10Cu12.5Ag5 metallic glass have been investigated by X-ray diffraction and transmission electron microscopy analyses. It was found that the quasicrystalline phase can precipitate from the glassy state and the supercooled liquid of the alloy over a wide range of annealing temperatures. After optimizing the heat-treatment conditions, the volume fraction of the quasicrystalline phase in the alloy can reach as high as about 80%. Investigation of the thermal stability of the quasicrystalline phase demonstrates that it is very stable when the annealing temperature is below the glass transformation temperature T g of the alloy.
14 citations
TL;DR: In this paper, the distribution of Al atoms in a nanocrystalline Fe88Zr7B3Al2 soft magnet with optimal magnetic performance was investigated using ion ion microscopy.
Abstract: Atom probe field ion microscopy was employed to investigate the distribution of Al in a nanocrystalline Fe88Zr7B3Al2 soft magnet with optimal magnetic performance. The atom probe concentration depth profiles show that the Al atoms preferentially partition into the residual amorphous phase, and the partitioning factor of Al is approximately five times larger in the amorphous phase than in the bcc Fe phase. Based on the experimental results, the beneficial effect of the addition of Al on the soft magnetic properties is attributed to the change of the inherent magnetostriction constant of the residual amorphous phase induced by Al partitioning.
9 citations