https://www.tcd.ie/Physics/people/Graham.Cross/SF%20Poster%202011/Schuh-ActaMater07-Mechanical%20behaviour%20of%20amorphous%20alloys.pdf

Mechanical behavior of amorphous alloys

Plastic deformation in metallic glasses

The provision of efficient electron and ion transport is a critical issue in an exciting new group of materials based on lithium metal phosphates that are important as cathodes for lithium-ion batteries. Much interest centres on olivine-type LiFePO(4), the most prominent member of this family. Whereas the one-dimensional lithium-ion mobility in this framework is high, the electronically insulating phosphate groups that benefit the voltage also isolate the redox centres within the lattice. The pristine compound is a very poor conductor (sigma approximately 10(-9) S cm(-1)), thus limiting its electrochemical response. One approach to overcome this is to include conductive phases, increasing its capacity to near-theoretical values. There have also been attempts to alter the inherent conductivity of the lattice by doping it with a supervalent ion. Compositions were reported to be black p-type semiconductors with conductivities of approximately 10(-2) S cm(-1) arising from minority Fe(3+) hole carriers. Our results for doped (and undoped) LiMPO(4) (M = Fe, Ni) show that a percolating nano-network of metal-rich phosphides are responsible for the enhanced conductivity. We believe our demonstration of non-carbonaceous-network grain-boundary conduction to be the first in these materials, and that it holds promise for other insulating phosphates.

Nano-network electronic conduction in iron and nickel olivine phosphates.

REVIEW ARTICLE: Glassy metals

Amorphous metallic alloys, also called metallic glasses, are of considerable technological importance. The metastability of these systems, which gives rise to various rearrangement processes at elevated temperatures, calls for an understanding of their diffusional behavior. From the fundamental point of view, these metallic glasses are the paradigm of dense random packing. Since the recent discovery of bulk metallic glasses it has become possible to measure atomic diffusion in the supercooled liquid state and to study the dynamics of the liquid-to-glass transition in metallic systems. In the present article the authors review experimental results and computer simulations on diffusion in metallic glasses and supercooled melts. They consider in detail the experimental techniques, the temperature dependence of diffusion, effects of structural relaxation, the atom-size dependence, the pressure dependence, the isotope effect, diffusion under irradiation, and molecular-dynamics simulations. It is shown that diffusion in metallic glasses is significantly different from diffusion in crystalline metals and involves thermally activated, highly collective atomic processes. These processes appear to be closely related to low-frequency excitations. Similar thermally activated collective processes were also found to mediate diffusion in the supercooled liquid state well above the caloric glass transition temperature. This strongly supports the mode-coupling scenario of the glass transition, which predicts an arrest of liquidlike flow already at a critical temperature well above the caloric glass transition temperature.

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Diffusion in Metallic Glasses and Supercooled Melts

An apparatus is described which permits for the first time the resolution of anelastic relaxation effects in evaporated metallic thin films and ion-implanted surface layers of silicon. The composite samples consist of the film or layer of interest on a carrier substrate having the form of a thin cantilevered reed. Low external losses and an exceptionally good span of operating frequencies are obtained by integrally bonding the substrate to a supporting pedestal and by using electrostatic drive and detection for the transverse modes of vibration. The internal friction can be measured with relatively simply instrumentation, at pressures below 10-5 (1.33 × 10-3 Pa) and over the temperature range -190°C to 550°C. The apparatus has considerable versatility for work in a number of areas, including the investigation of metallic foils prepared by splat-cooling.

Vibrating reed internal friction apparatus for films and foils

The amorphous ferromagnetic alloy ${\mathrm{Fe}}_{75}$${\mathrm{P}}_{15}$${\mathrm{C}}_{10}$ has been found to respond reversibly to magnetic annealing treatments. The response has been studied (a) by measurements of the $\ensuremath{\Delta}E$ effect, which is unusually large, (b) by measurements of the magnetostriction, and (c) by torque curves which yield a value of 550 erg/${\mathrm{cm}}^{3}$ for the uniaxial anisotropy parameter ${K}_{u}$. Internal-friction measurements reveal that the alloy is also susceptible to stress-induced ordering, with an activation energy of 2.2 eV.

Magnetic Annealing and Directional Ordering of an Amorphous Ferromagnetic Alloy

Hydrogen-related internal friction peaks in metallic glasses

A Gorsky relaxation associated with the long-range diffusion of hydrogen has been observed for the first time in a metallic glass. The diffusion parameters for amorphous ${\mathrm{Pd}}_{80}$${\mathrm{Si}}_{20}$ are ${Q}_{D}=0.25$ eV and ${D}_{0}=0.003$ ${\mathrm{cm}}^{2}$/sec. From the characteristics of a complementary reorientation relaxation, it is concluded that the interstitial sites occupied by hydrogen possess a distinctly asymmetric character.

Gorsky relaxation and hydrogen diffusion in the metallic glass Pd 80 Si 20

Room‐temperature values of the thermal‐expansion coefficient, thermal diffusivity, thermal conductivity, density, Young's modulus E, and the temperature coefficient (1/E) dE/dT are presented for two splat‐cooled amorphous alloys of composition (in atomic percent) Pd82Si18 and Fe75P15C10. Values of E were obtained from the flexural resonant frequencies of cantilever mounted reeds; the thermal properties were derived from internal friction measurements giving the height and location of the thermoelastic ``transverse thermal current'' peak. Compared to crystalline alloys, the amorphous samples are poorer thermal conductors but exhibit a comparable expansion behavior. In view of the small density difference between the amorphous and crystalline states, the most striking difference observed was the lower elastic modulus of the amorphous alloys. The present results supplement a growing body of evidence that materials in the amorphous condition may have a Young's or shear modulus which is typically 20–40% less t...

W. C. Pritchet

Papers

Vibrating reed internal friction apparatus for films and foils

Magnetic Annealing and Directional Ordering of an Amorphous Ferromagnetic Alloy

Hydrogen-related internal friction peaks in metallic glasses

Gorsky relaxation and hydrogen diffusion in the metallic glass Pd 80 Si 20

Some physical properties of two amorphous metallic alloys