The strain rate dependence of plastic deformation of Ce60Al15Cu10Ni15 bulk metallic glass was studied by nanoindentation. Even though the ratio of room temperature to the glass transition temperature was very high (0.72) for this alloy, the plastic deformation was dominated by shear banding under nanoindentation. The alloy exhibited a critical loading rate dependent serrated flow feature. That is, with increasing loading rate, the alloy exhibited a transition from less prominent serrated flow to pronounced serrated flow during continuous loading but from serrated to smoother flow during stepped loading.

The dry sliding friction coefficient μ and the wear volume loss W, in a zirconium-based bulk metallic glass (BMG) under high-frequency (50 Hz) reciprocating conditions, were investigated with the objective of assessing the influence of free volume and crystallization on the wear behavior of amorphous metals. The BMG samples were annealed either below the glass transition temperature Tg to induce structural relaxation and hence reduce the free volume that controls plasticity through shear-band formation or above Tg to crystallize the amorphous BMG prior to wear testing. Results show that the wear behavior of both the as-cast and relaxed glasses was dominated by the oxidation of the surface layers. A sharp transition in the contact electrical resistance complemented by a marked increase in μ was noted. This was attributed to the formation of a thick tribo film with high oxygen concentration and its subsequent delamination. The μ values, before as well as after the transition, in the relaxed glasses were similar to those for the as-cast alloy. However, a gradual decrease in W with annealing temperature was observed. A good correlation between W and nanohardness was noted, implying that the intrinsic hardness in the BMGs controlled the wear rate.

Two different types of metallic glasses, a metal-metal-based and a metal-metalloid-based one, in both bulk and ribbon form (i.e., produced with very different quenching rates) are compared with respect to their structural relaxation behavior during continuous heating (2 K/min) in a vibrating-reed set-up (frequencies 0.2–5 kHz). The variation of damping as a function of temperature, time, and strain amplitude is shown as a measure of the content of structural relaxation centers, whose nature is studied by means of artificially introduced irregularities into the amorphous structure (i.e., by cold rolling and by hydrogen charging). The results indicate that the hydrogen damping peak, which is only observed in the Zr-based glass, is more probably due to hydrogen reorientation jumps than due to reorientation of hydrogen-related, dislocation-like distortion fields although the latter cannot be ruled out. A pronounced deformation damping peak could not be found in contrast to earlier results in the literature, probably owing to the selected degrees of deformation.

The development of bulk metallic glasses and composites for improving the mechanical properties has occurred with the discovery of many ductile metallic glasses and glass matrix composites with second phase dispersions with different length scales. This article reviews the processing, microstructure development, and resulting mechanical properties of Zr-, Ti-, Cu-, Mg-, Fe-, and Ni-based glassy alloys and also considers the superiority of composite materials containing different phases for enhancing the strength, ductility, and toughness, even leading to a “work-hardening-like” behavior. The morphology, shape, and length scale of the second phase dispersions are crucial for the delocalization of shear bands. The article concludes with some comments regarding future directions of the investigations of spatially inhomogeneous metallic glasses.

The review of corrosion performance of a number of alloy systems documents several metallic glasses with corrosion resistance superior to that of crystalline metals. In other cases, the metallic glasses do not have superior corrosion resistance. The nature of corrosion resistance of the metallic glasses is often directly related to the development of a passive film (protective layer) on the reactive alloy substrate, increased durability of the passive film, or enhanced resistance to localized corrosion where the passive film is broken or damaged. Potential mechanical/environmental degradation processes include stress-corrosion cracking, corrosion fatigue, various forms of hydrogen damage, wear, and abrasion. The availability of bulk metallic glasses in significant three-dimensional sizes will stimulate important work in these areas that will enhance the fundamental understanding of the corrosion behavior and mechanical interactions and develop design guidelines and materials properties database for designers and engineers.

Starting with a bulk metallic glass-forming alloy Mg65Cu18Ni6Y11, we prepared in situ composites by increasing the Mg content in a series of alloys, Mgx(Cu0.51Ni0.17Y0.32)100−x (65 ≤ x ≤ 90), via copper mold casting of rods 4 mm in diameter. The fully glassy alloy at x = 65 showed a compressive fracture strength of 755 MPa but no observable macroscopic plasticity prior to failure. Metallic glass-based composites were formed when the Mg content was increased. For x > 80, the glassy phase no longer existed in the as-cast rods. In the composition range of 80 ≤ x ≤ 85, needle-shaped Mg solution with a 14H-type long period stacking (LPS) structure appeared as the primary phase in the as-cast microstructure. On further increase of the Mg content up to x = 90, the solidified primary phase became 2H-Mg, coexisting with the remaining eutectic structure. The best combination of mechanical properties was obtained for the alloy at x = 81.5, which showed a fracture strength of 665 MPa and a compressive plastic strain of 11.6%. The specific strength of this alloy was 2.8 × 105 N m kg−1, much higher than conventional cast magnesium alloys. The mechanical properties are discussed in light of the phase selection and microstructural features uncovered in microscopy examinations.

Cu47.5Zr47.5Al5 was prepared by arc melting and solidified in situ by suction casting into 2–5-mm-diameter rods under various cooling rates (200–2000 K/s). The microstructure was investigated along the length of the rods by electron microscopy, differential scanning calorimetry and mechanical properties were investigated under compression. The microstructure of differently prepared specimens consists of macroscopic spherical shape chemically inhomogeneous regions together with a low volume fraction of randomly distributed CuZr B2 phase embedded in a 2–7 nm size clustered “glassy-martensite” matrix. The as-cast specimens show high yield strength (1721 MPa), pronounced work-hardening behavior up to 2116 MPa and large fracture strain up to 12.1–15.1%. The fracture strain decreases with increasing casting diameter. The presence of chemical inhomogenities and nanoscale “glassy-martensite” features are beneficial for improving the inherent ductility of the metallic glass.

In the present study, we show by tailoring the combinations of the bonding energy among the elements in the liquid state, glass forming ability and compressive mechanical properties of the metallic glasses (MGs) can be improved. The mixing enthalpy values for binary atom pairs in the ternary Mg–Ni–Gd alloys (Mg–Ni: −12 kJ/mol, Mg–Gd: −27 kJ/mol, Ni–Gd: −161 kJ/mol) covers a wide range, although they are all negative. Mg-rich Mg–Ni–Gd (Mg > 70 at.%) alloys can be readily solidified into an amorphous state in a wide composition range up to 4 mm in diameter using the injection casting method; they exhibit the highest level of glass transition temperature Tg among those reported in Mg-based MGs so far. In particular, Mg-rich Mg–Ni–Gd bulk metallic glasses with 10–15 at.% Ni and 10–15 at.% Gd exhibit high strength over 900 MPa and large plastic strain up to ∼2% during compressive loading.

In this article, we report a simple and inexpensive approach to micromolding of complex, three-dimensional, high aspect ratio structures (with non-line-of-sight features) out of a high-strength amorphous metal. Inexpensive sacrificial silicon molds were created using lithography and etching techniques originally developed for integrated circuit production by the microelectronics industry and later adopted for microelectromechanical (MEMS) manufacturing. Multiple silicon layers were stacked, and the metallic glass was forced into the cavities under heat and pressure in an open air environment. Following cooling, the metallic structures were released by etching the silicon away in a potassium hydroxide (KOH) bath. Process studies showed that temperature is the most significant variable governing mold-filling. Transmission electron microscopy (TEM) sections of the mold/glass interface showed successful replication of features with characteristic dimensions on the order of 10 nanometers and no discernible gap between the silicon and the metallic glass. This scalable micromolding process leverages the inexpensive and readily available aspects of silicon lithography to economically support the mass customization (low volume production) of metal microcomponents without elaborate infrastructure needs.

Iron-based bulk metallic glasses (BMGs) are characterized by high fracture strengths and elastic moduli, with some exhibiting fracture strengths near 4 GPa, 2–3 times those of conventional high-strength steels. Among the Fe-based BMGs, the non-ferromagnetic ones, designated “non-ferromagnetic amorphous steel alloys” by two of the present authors [S.J. Poon et al.: Appl. Phys. Lett.83, 1131 (2003)], have glass-forming ability high enough to form single-phase glassy rods with diameters reaching 16 mm. Fe-based BMGs designed for structural applications must exhibit some plasticity under compression. However, the role of alloy composition on plastic and brittle failures in metallic glasses is largely unknown. In view of a recently observed correlation that exists between plasticity and Poisson’s ratio for BMGs, compositional effects on plasticity and elastic properties in amorphous steels were investigated. For the new amorphous steels, fracture strengths as high as 4.4 GPa and plastic strains reaching ∼0.8% were measured. Plastic failure instead of brittle failure was observed as the Poisson’s ratio approached 0.32 from below. Investigation of the relationship between the elastic moduli of the alloys and those of the alloying elements revealed that interatomic interactions in addition to the elastic moduli of the alloying elements must be considered in designing ductile Fe-based BMGs. The prospects for attaining high fracture toughness in Fe-based BMGs are discussed in this article.

Cylindrical Cu42.5Ti41.5Ni7.5Zr2.5Hf5Si1 bulk metallic glass with a diameter of 2 mm was fabricated by copper-mold casting. X-ray diffraction and differential scanning calorimetry analysis of the material showed that the alloy has a homogenous amorphous structure and high glass-forming ability. However, detailed observation by transmission electron microscopy revealed that a kind of nanocrystal with size of about 20 nm is sparsely distributed in the glass matrix. Nanobeam electron diffraction experiments indicated that the nanocrystal has a face-centered cubic crystalline structure. Room-temperature compression tests revealed that the alloy has a high fracture strength of 2250 MPa and obvious plastic strain of about 5.3%. Nanoindentation tests revealed that the as-cast alloy exhibits obviously serrated flow over a wide range of loading rate from 0.5 to 10 mN/min.

The mechanical properties of a new Fe41Co7Cr15Mo14Y2C15B6 bulk glassy alloy were studied by impact bending, compression, and hardness tests carried out at room temperature. The compressive fracture strength, elastic strain to fracture, Young’s modulus and Vickers hardness were measured to be 3.5 GPa, 1.5%, 265 GPa, and 1253 kg mm−2, respectively. The fracture mode of the glassy alloy under uniaxial compression is different from those of other bulk metallic glasses in that this fracture mode causes the samples to be broken, in an exploding manner, into a large number of micrometer-scale pieces. The fracture mechanisms of this bulk glassy alloy under bending and uniaxial compression are discussed based on the observation of the fracture surfaces. Vickers indentation tests indicate that the structure of the glassy ingot may be inhomogeneous.

We report measurements of the elastic properties of Zr-based bulk metallic glasses, Zr52.5Cu17.9Ni14.6Al10Ti5, Zr50Cu30Ni10Al10, and Zr50Cu40Al10 between 5 K and 300 K. Both the shear and longitudinal modulus have been measured as a function of temperature, allowing accurate determination of the Poisson’s ratio and the related ratio of bulk modulus to shear modulus, K/G. These data make it possible to assess the influence of the alloy’s composition on the mechanical properties and enable an evaluation of the correlation between the elastic moduli and the ductility of the alloys.

Using an infrared camera, the plastic deformation of a relaxed Zr52.5Cu17.9Ni14.6Al10.0Ti5.0 bulk-metallic glass in a moderately high strain rate compression was observed in situ. The specimen exhibits an inhomogeneous deformation, which is manifested by serrated plastic flow, shear banding, and obvious work softening. Shear-banding operations were observed throughout the plastic deformation. Shear-banding operations started before the nominal yielding; shear bands could not block each other, but their interaction seems to accelerate the plastic deformation. A significant increase in the specimen’s temperature was observed due to shear banding.

The stress-life fatigue behavior and fracture morphology of a (Cu60Zr30Ti10)99Sn1 bulk-metallic glass alloy was investigated under both three-point and four-point bending conditions. For all stress levels tested, the fatigue lifetimes tended to be higher for the three-point loading condition. The fatigue endurance limits (defined as 107 cycles without failure), based on the applied stress range, for three-point and four-point loading conditions were approximately 475 MPa and 350 MPa, respectively. All fracture surfaces were found to be composed of four main regions: a crack-initiation site, a stable crack-growth region, an unstable fast-fracture region, and a melting region. Finely spaced parallel marks, similar to fatigue striations found in crystalline alloys, oriented somewhat perpendicular to the direction of crack propagation were observed in the stable crack-growth region. Analyses of these marks found that their spacing increased with increasing stress-intensity-factor range. Damage was found to initiate from preexisting defects present on or near the surface.

The anisotropic atomic structure in a Zr41.2Ti13.8Cu12.5Ni10Be22.5 metallic glass strained during uniaxial tensile creep at 598 K was studied at room temperature using high-energy x-ray diffraction. Changes in the atomic structure were examined by comparing the total scattering function [S(Q)] and the reduced pair distribution function [G(r)] of the creep to that of a companion specimen subjected to the same heat treatment only. Two-dimensional maps of the ΔS(Q) and its Fourier transformation demonstrate the distribution in the bond orientation anisotropy increases with increasing total strain. A fit of the reduced pair distribution function using a simplified two-component model suggests that the bond length changes in the deformed creep samples are not uniform.

High strain-rate compression experiments were performed with a split-Hopkinson pressure bar (SHPB) at 500–4000/s on cylindrical samples of a Zr-based bulk metallic glass (LM-1) in both the fully amorphous and annealed conditions. The effects of changes to the specimen geometry (i.e., L/D ratio) and the material heat treatment [i.e., annealing versus amorphous (as-received)], on the peak stress, strain-to-failure, and failure behavior were determined with the aid of an in situ video obtained by using a high-speed digital camera in conjunction with the split-Hopkinson pressure bar (SHPB). Examination of the in situ video recordings and light optical microscopy showed that the failed samples revealed preferential failure initiating at the sample ends due to stress concentration at the sample-insert interface. A new insert design was developed using transient, elastic-plastic finite-element simulations to reduce the effects of these stress concentrations. SHPB testing, combined with in situ video, subsequently revealed that this new experimental configuration promoted failure within the gage length and away from the sample ends in the samples tested. Significant effects of specimen geometry, insert design, and annealing on the apparent values of the peak stress, strain-to-failure, and fracture behavior were exhibited.

Results are presented on the shock response of a zirconium-based bulk metallic glass (BMG), Zr41.25Ti13.75Ni10Cu12.5Be22.5, subjected to planar impact loading. An 82.5-mm bore single-stage gas-gun facility at Case Western Reserve University, Cleveland, OH, was used to conduct the shock experiments. The particle velocity profiles, measured at the back (free) surface of the target plate by using the velocity interferometer system for any reflector (VISAR), were analyzed to (i) better understand the structure of shock waves in BMG subjected to planar shock compression, (ii) estimate residual spall strength of the BMG after different levels of shock compression, and (iii) obtain the Hugoniot elastic limit (HEL) of the material. The spall strength was found to decrease moderately with increasing levels of the applied normal impact stress. The spall strength at a shock-induced stress of 4.4 GPa was 3.5 GPa while the spall strengths at shock-induced stresses of 5.1, 6.0, and 7.0 GPa were 2.72, 2.35, and 2.33 GPa, respectively. The HEL was estimated to be 6.15 GPa.

We have investigated atomic structure of a Fe81B13Si4C2 metallic glass after mechanical creep deformation. We determined the structure function and pair density function resolved for azimuthal angle using x-ray scattering and a two-dimensional detector. The results are analyzed by the spherical harmonics expansion, and are compared to the often-used simple analysis of the anisotropic pair density function determined by measuring the structure function along two directions with respect to the stress. We observed uniaxial structural anisotropy in a sample deformed during creep experiment. The observed macroscopic shear strain is explained in terms of local bond anisotropy induced by deformation at elevated temperature. The bond anisotropy is a “memory” of this deformation after load was removed. We showed that use of sine-Fourier transformation to anisotropic glass results in systematic errors in the atomic pair distribution function.