Amorphous alloys were first developed over 40 years ago and found applications as magnetic core or reinforcement added to other materials. The scope of applications is limited due to the small thickness in the region of only tens of microns. The research effort in the past two decades, mainly pioneered by a Japanese- and a US-group of scientists, has substantially relaxed this size constrain. Some bulk metallic glasses can have tensile strength up to 3000 MPa with good corrosion resistance, reasonable toughness, low internal friction and good processability. Bulk metallic glasses are now being used in consumer electronic industries, sporting goods industries, etc. In this paper, the authors reviewed the recent development of new alloy systems of bulk metallic glasses. The properties and processing technologies relevant to the industrial applications of these alloys are also discussed here. The behaviors of bulk metallic glasses under extreme conditions such as high pressure and low temperature are especially addressed in this review. In order that the scope of applications can be broadened, the understanding of the glass-forming criteria is important for the design of new alloy systems and also the processing techniques.

https://www.tcd.ie/Physics/people/Graham.Cross/SF%20Poster%202011/Shek-MaterSciEng04-Bulk%20Metallic%20Glasses.pdf

Bulk metallic glasses

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

Mechanical behavior of amorphous alloys

A microscopic mechanism for steady state inhomogeneous flow in metallic glasses

Atomic-level structure and structure–property relationship in metallic glasses

Shear-banding is a ubiquitous plastic-deformation mode in materials. In metallic glasses, shear bands are particularly important as they play the decisive role in controlling plasticity and failure at room temperature. While there have been several reviews on the general mechanical properties of metallic glasses, a pressing need remains for an overview focused exclusively on shear bands, which have received tremendous attention in the past several years. This article attempts to provide a comprehensive and up-to-date review on the rapid progress achieved very recently on this subject. We describe the shear bands from the inside out, and treat key materials-science issues of general interest, including the initiation of shear localization starting from shear transformations, the temperature and velocity reached in the propagating or sliding band, the structural evolution inside the shear-band material, and the parameters that strongly influence shear-banding. Several new discoveries and concepts, such as stick-slip cold shear-banding and strength/plasticity enhancement at sub-micrometer sample sizes, will also be highlighted. The understanding built-up from these accounts will be used to explain the successful control of shear bands achieved so far in the laboratory. The review also identifies a number of key remaining questions to be answered, and presents an outlook for the field.

Shear bands in metallic glasses

The longitudinal and transverse sound velocities and Vickers hardness of metallic glasses (Pd1 − xNix)0.80P0.20, (Pd1 − xFex)0.80P0.20 and (Pt1 − xNix)0.75P0.25 have been measured. The elastic constants at room temperature exhibit a positive deviation with composition χ from linearity whereas the hardness shows a negative deviation. The increase in elastic constants has been attributed to a denser packing of the alloys on mixing. The reduced hardness HrH/μ versus χ exhibits a remarkable similarity to a Tg versus χ relationship. This seems to indicate that flow mechanisms involved in metallic glasses above and below the glass-transition temperature are of similar origins. It is the excess entropy of disorder associated with alloying which lowers the hardness as well as the viscosity of metallic glasses. The metallic glasses possess in general a relatively high Poisson's ratio ν ≈ 0.40 and a shear modulus approaching that of the noble metals Cu, Ag and Au. Among the metallic glasses observed, the PtP glasses exhibit the highest ν = 0.42, whereas the glasses containing Fe tend to have lower values. The phenomenon that the conduction electrons in the glassy alloys behave as in the noble metals may be partly attributed to the filling of d shell orbitals of the transition metals in the PtP, PdP and NiP alloys. The high ν of metallic glasses is believed to be responsible for the ductile behavior of these glasses. Poisson's ratio ν of metallic glasses was observed to decrease with decreasing temperature. It is suggested that the decreasing ν with falling temperature causes the rapid increase in the fracture strength of Fe-based glasses.

Elastic constants, hardness and their implications to flow properties of metallic glasses

Thermal expansion and density of (Pd1−xNix)0.80P0.20 and (Pt1−yNiy)0.75P0.25 alloys in their various states have been measured from room temperature to the glass transition temperature Tg. The thermal expansion of the glassy alloys at room temperature varies linearly with x and y and is 10 to 20% higher than that of corresponding pure metals. The thermal expansion of the undercooled alloy liquids near Tg as well as the molar volume v deduced from the density of glasses in contrast exhibits a negative deviation with composition x and y. This behavior is in line with the previously reported negative deviation of the glass transition temperature of these glassy alloys with metal content and may be explained in terms of excess volume associated with a mixture of hard spheres.

Thermal expansion and density of glassy PdNiP and PtNiP alloys

Disclosed is an optical communication system comprising at least two optical fibers of dissimilar core sizes, joined by a fusion splice. In one embodiment, the larger-core fiber is a communication fiber, and the smaller-core fiber is an erbium-doped amplifier fiber. A taper region is included adjacent the splice. The diameter of the smaller-core fiber increases within the taper region as the splice is approached along the smaller-core fiber. The taper region is substantially free of constrictions. As a consequence of the taper region, the optical losses associated with the splice are relatively low, even when there is relatively high mismatch between the mode field diameters (at a signal wavelength) in the respective fibers.

Optical communication system comprising a fiber amplifier

The melt-spun icosahedral phase of ${\mathrm{Al}}_{86}$${\mathrm{Mn}}_{14}$ exhibits a density (=3.26\ifmmode\pm\else\textpm\fi{}0.06 g/${\mathrm{cm}}^{3}$) only slightly less dense by \ensuremath{\sim}1% and a specific heat higher by \ensuremath{\sim}0.20 cal/mol K compared with the stable orthorhombic phase. The room-temperature Young's modulus, however, is found to decrease drastically by \ensuremath{\sim}20% from 12.60\ifmmode\times\else\texttimes\fi{}${10}^{11}$ dyn/${\mathrm{cm}}^{2}$ for the orthorhombic phase to 10.12\ifmmode\times\else\texttimes\fi{}${10}^{11}$ dyn/${\mathrm{cm}}^{2}$ for the icosahedral phase. The activation energy and heat of the icosahedral-orthorhombic transformation are found to be 53 kcal/mol and 560 cal/mol, respectively. The changes in these physical properties observed here are in many ways similar to those reported for many metal glasses. It is thus inferred that the icosahedral ${\mathrm{Al}}_{86}$${\mathrm{Mn}}_{14}$ consists of a highly disordered defective structure.

Density, Young's modulus, specific heat, and stability of icosahedral Al86Mn14.

This study shows that the transition in slope of static fatigue (log fracture stress vs. log time to failure) of fused silica fibers, is an intrinsic property of the glass which is modified by the presence of coating materials. The transition for fibers in water at 90°C occurs in the 300–400 Ksi range and is characterized by a change in slope and intercept. The slopes and intercepts preceding the transitions are dependent upon zero stress soak time in water at 90°C, however in the transition region they are unchanged by this treatment. At a stress level of about 160 Ksi the transition region appears to terminate in a more normal fatigue dependence. This may possibly be a fatigue limit. These observations suggest that changes will be required in the theories correlating static fatigue with crack growth parameters as determined from macro-crack experiments. Long-term extrapolations of fatigue data will accordingly have to incorporate modifications based on such changes.

J. T. Krause

Papers

Elastic constants, hardness and their implications to flow properties of metallic glasses

Thermal expansion and density of glassy PdNiP and PtNiP alloys

Optical communication system comprising a fiber amplifier

Density, Young's modulus, specific heat, and stability of icosahedral Al86Mn14.

Zero stress strength reduction and transitions in static fatigue of fused silica fiber lightguides