Mary Laura Lind

Designing metallic glass matrix composites with high toughness and tensile ductility

The selection and design of modern high-performance structural engineering materials is driven by optimizing combinations of mechanical properties such as strength, ductility, toughness, elasticity and requirements for predictable and graceful (non-catastrophic) failure in service. Highly processable bulk metallic glasses (BMGs) are a new class of engineering materials and have attracted significant technological interest. Although many BMGs exhibit high strength and show substantial fracture toughness, they lack ductility and fail in an apparently brittle manner in unconstrained loading geometries. For instance, some BMGs exhibit significant plastic deformation in compression or bending tests, but all exhibit negligible plasticity (<0.5% strain) in uniaxial tension. To overcome brittle failure in tension, BMG–matrix composites have been introduced. The inhomogeneous microstructure with isolated dendrites in a BMG matrix stabilizes the glass against the catastrophic failure associated with unlimited extension of a shear band and results in enhanced global plasticity and more graceful failure. Tensile strengths of ∼1 GPa, tensile ductility of ∼2–3 per cent, and an enhanced mode I fracture toughness of K1C ≈ 40 MPa m1/2 were reported. Building on this approach, we have developed ‘designed composites’ by matching fundamental mechanical and microstructural length scales. Here, we report titanium–zirconium-based BMG composites with room-temperature tensile ductility exceeding 10 per cent, yield strengths of 1.2–1.5 GPa, K1C up to ∼170 MPa m1/2, and fracture energies for crack propagation as high as G1C ≈ 340 kJ m-2. The K1C and G1C values equal or surpass those achievable in the toughest titanium or steel alloys, placing BMG composites among the toughest known materials.

Development of tough, low-density titanium-based bulk metallic glass matrix composites with tensile ductility

The mechanical properties of bulk metallic glasses (BMGs) and their composites have been under intense investigation for many years, owing to their unique combination of high strength and elastic limit. However, because of their highly localized deformation mechanism, BMGs are typically considered to be brittle materials and are not suitable for structural applications. Recently, highly-toughened BMG composites have been created in a Zr–Ti-based system with mechanical properties comparable with high-performance crystalline alloys. In this work, we present a series of low-density, Ti-based BMG composites with combinations of high strength, tensile ductility, and excellent fracture toughness.

Tailoring the structure of thin film nanocomposite membranes to achieve seawater RO membrane performance.

Herein we report on the formation and characterization of pure polyamide thin film composite (TFC) and zeolite-polyamide thin film nanocomposite (TFN) reverse osmosis (RO) membranes. Four different physical-chemical post-treatment combinations were applied after the interfacial polymerization reaction to change the molecular structure of polyamide and zeolite-polyamide thin films. Both TFC and TFN hand-cast membranes were more permeable, hydrophilic, and rough than a commercial seawater RO membrane. Salt rejection by TFN membranes was consistently below that of hand-cast TFC membranes; however, two TFN membranes exhibited 32 g/L NaCl rejections above 99.4%, which was better than the commercial membrane under the test conditions employed. The nearly defect-free TFN films that produced such high rejections were achieved only with wet curing, regardless of other post-treatments. Polyamide films formed in the presence of zeolite nanoparticles were less cross-linked than similarly cast pure polyamide films. At the very low nanoparticle loadings evaluated, differences between pure polyamide and zeolite-polyamide membrane water and salt permeability correlated weakly with extent of cross-linking of the polyamide film, which suggests that defects and molecular-sieving largely govern transport through zeolite-polyamide thin film nanocomposite membranes.

Strong configurational dependence of elastic properties for a binary model metallic glass

In this work, the strong dependence of elastic properties on configurational changes in a Cu–Zr binary metallic glass assessed by molecular dynamics simulations is reported. By directly evaluating the temperature dependence and configurational potential energy dependence of elastic constants, the shear modulus dependence on the specific configurational inherent state of metallic glasses is shown to be much stronger than the dependence on Debye-Gruneisen thermal expansion.

Thermal and elastic properties of Cu–Zr–Be bulk metallic glass forming alloys

The compositional dependence of thermal and elastic properties of Cu–Zr–Be ternary bulk metallic glass forming alloys was systematically studied. There exists a linear relationship between the glass transition temperature Tg and the total Zr concentration. G decreases linearly with increasing Zr concentration as well. The results also show that Tg, shear modulus G, and Poissons ratio nu are very sensitive to changes in compositions. Low Tg, low G, and relatively high nu can be achieved with high Zr and Ti concentration.

Dynamical and quasistatic structural relaxation paths in Pd40Ni40P20 glass

By sequential heat treatment of a Pd_(40)Ni_(40)P_(20) metallic glass at temperatures and durations for which α-relaxation is not possible, dynamic, and quasistatic relaxation paths below the glass transition are identified via ex situ ultrasonic measurements following each heat treatment. The dynamic relaxation paths are associated with hopping between nonequilibrium potential energy states of the glass, while the quasistatic relaxation path is associated with reversible β-relaxation events toward quasiequilibrium states. These quasiequilibrium states are identified with secondary potential energy minima that exist within the inherent energy minimum of the glass, thereby supporting the concept of the sub-basin/metabasin organization of the potential-energy landscape.

Analysis of the Water Permeability of Linde Type A Zeolites in Reverse Osmosis

In this paper, we apply the Hagan-Poiseuille Model and the resistance model to perform an original analysis of previous experimental studies of water transport through polycrystalline Linde Type A (LTA) zeolite membranes and nanocomposite polymer/LTA membranes. From our analysis we estimate the intrinsic water permeability of LTA zeolites and the zeolite/polymer interface. We find that the permeability of a single LTA crystal is significantly greater than the intrinsic permeability of a commercial seawater reverse osmosis membrane or a commercial cellulose-acetate forward osmosis membrane.

Removal of pesticide toxicity by cysteine-capped Ag nanoparticles and study of their adsorption kinetics

A new method has been developed for one-step synthesis of cysteine-capped Ag nanoparticles. The particles have been characterized by several techniques, including ultraviolet–visible spectroscopy, infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The interaction of these nanoparticles has been seen with two pesticides, namely, chlorpyrifos and malathion, which are major water pollutants.