Mechanical Behavior Of Metallic Glasses Research Articles

Mechanical behavior of amorphous alloys

The mechanical properties of amorphous alloys have proven both scientifically unique and of potential practical interest, although the underlying deformation physics of these materials remain less firmly established as compared with crystalline alloys. In this article, we review recent advances in understanding the mechanical behavior of metallic glasses, with particular emphasis on the deformation and fracture mechanisms. Atomistic as well as continuum modeling and experimental work on elasticity, plastic flow and localization, fracture and fatigue are all discussed, and theoretical developments are connected, where possible, with macroscopic experimental responses. The role of glass structure on mechanical properties, and conversely, the effect of deformation upon glass structure, are also described. The mechanical properties of metallic glass-derivative materials – including in situ and ex situ composites, foams and nanocrystal-reinforced glasses – are reviewed as well. Finally, we identify a number of important unresolved issues for the field.

Anelastic deformation of a Pd40Cu30Ni10P20 bulk metallic glass during nanoindentation

Time-dependent deformation processes during nanoindentation have been investigated on a Pd40Cu30Ni10P20 bulk metallic glass. Deformation under constant load has been studied as a function of prior loading rate and temperature. The constant-load displacement of the indenter into the sample shows classic relaxation kinetics and reveals the importance of anelasticity for the mechanical behavior of metallic glasses at the nanoscale.

Specimen-geometry effects on mechanical behavior of metallic glasses

The mechanical behavior of metallic glasses under bending, compression, impact, and fatigue experiments varies, depending on the specimen geometry. The dependence of the mechanical behavior of metallic glasses on specimen geometries is reviewed and studied in this work. Different specimen geometries are found to influence the shear-band formation and deformation processes, resulting in the variations of mechanical properties. The understanding of specimen-geometry effects on the mechanical behavior of metallic glasses is critical to the improvement of mechanical properties of metallic glasses.

Preface to the viewpoint set on mechanical behavior of metallic glasses

This work reports the use of a new high-temperature scanning indentation (HTSI) technique to monitor the physical changes occurring in thin-film metallic glasses (TFMGs) in situ during heat treatment at the local scale. Using this technique, based on high-speed nanoindentation performed during thermal cycles, the entire mechanical evolution with temperature of a binary model ZrCu TFMG was characterized in only a few hours. This approach enabled clear identification of the physical evolutions of the amorphous coatings in only one indentation experiment, highlighting in particular the metallic glass-to-supercooled liquid transition and crystallization process. In addition, the brittle-to-ductile transition was precisely characterized, with remarkable agreement with the literature. Moreover, the mechanical response of the ZrCu thin film was assessed in situ throughout the entire supercooled liquid stage, providing key kinetic information. Nanohardness measurements also enabled the crystallization fraction to be computed over time during the crystallization process. In addition, differential scanning calorimetry and high-temperature X-ray diffraction were performed for comparison purposes, with excellent agreement with the HTSI results. Through this model out-of-equilibrium thin-film study, both the efficiency and robustness of HTSI were demonstrated, providing a better understanding of the thermally activated mechanisms of small-scale systems.

Hardness and plastic deformation in a bulk metallic glass

An experimental investigation into the Vickers hardness and associated plastic deformation in as-cast and annealed Pd42Ni40P18 bulk metallic glass was conducted. In addition to the bulk indentation behavior, the deformation morphology underneath the indenter and its variation with annealing time was examined by employing the bonded interface technique. For both the bulk and the interface indentations, the trends in the shear band induced plastic deformation zone sizes with the indentation load agree well with those predicted from the expanding cavity model. However, the yield strength extracted from the indentation data is higher than that measured in uniaxial compression, indicating pressure sensitive plasticity. Results show that the as-cast as well as the partially crystallized alloys deform appreciably through the shear band mechanism, with semi-circular and radial shear band morphologies. The latter gets increasingly prominent with increasing annealing time. Atomic force microscopy of the deformation region reveals increasing shear band heights with load, consistent with nanoindentation results. Whereas the spacing between semicircular shear bands was found to be independent of their distance from the tip of the indenter for the as-cast alloy, it was found to increase linearly, after a small zone of constant spacing, in the annealed alloys. Implications of this study in understanding the mechanical behavior of metallic glasses and their derivatives are discussed.

Shear band formation and ductility of metallic glasses

Abstract Variations in microstructure and chemical compositions of the metallic glasses found in the literature, as well as an overall lack of experimental data on inhomogeneous behavior of metallic glass make the evaluation of the effects of shear band/fracture behavior on mechanical properties of metallic glasses difficult. Investigating the effect of strain localization alone on inhomogeneous flow seems to be a first step in approaching this problem. Mechanical behavior of metallic glasses at room temperature and various strain rates in tension and compression was investigated. Formation of multiple shear bands was observed at high strain rates. An increase in strain rate leads to enhanced ductility in tension, whereas, the ductility of the material in compression decreases with increasing strain rate. Differences in deformation processes in tension and compression were compared.

Peculiarities of the Mechanical Behavior of Metallic Glasses Investigated by Indentation Techniques

Peculiarities of the Mechanical Behavior of Metallic Glasses Investigated by Indentation Techniques

Superplastic behavior of a Zr–10Al–5Ti-–17.9Cu–14.6Ni metallic glass in the supercooled liquid region

The mechanical behavior of metallic glasses is characterized by either inhomogeneous or homogeneous deformation. Inhomogeneous deformation usually occurs when a metallic glass is deformed at room temperature (i.e., low temperature) and is characterized by the formation of localized shear bands, followed by the rapid propagation of these bands, and sudden fracture. Consequently, when a metallic glass is deformed under tension it exhibits only limited macroscopic plasticity ( 0.70T{sub g}), and the material can often exhibit significant plasticity, especially in the supercooled liquid (SL) region. In summary, large tensile ductility can generally be obtained in the supercooled liquid region from a metallic glass with a large {Delta}T. The exact deformation mechanism, however, and in particular whether an alloy deforms by Newtonian viscous flow remains a controversial issue. The purpose of this paper is to report an example of non-Newtonian behavior in a cast amorphous Zr-10Al-5Ti-17.9Cu-14.6Ni alloy in the supercooled liquid region.

Mechanical behavior of metallic glasses

This is a review of the present knowledge of the mechanical behavior of metallic glasses. It begins with a brief discussion of their structures and how these relate to the small change (about 1%) in mass density that occurs when a metallic glass is crystallized. Then the elastic, anelastic, plastic, and strength properties are reviewed. Mechanisms of plastic flow are discussed. A quantitative dislocation model that successfully predicts the observed yield stresses is presented. Needs for producing future understanding are outlined.