On the toughening of bulk metallic glasses (BMGs), successful results in the phase-separated Zr63.8Ni16.2Cu15Al5 BMG have achieved compressive ductility over 15% through the computational-thermodynamic approach. In this study, the phase-separated Zr63.8Ni16.2Cu15Al5 BMG was compressed to nominal strains of 3%, 7%, and 10% at low strain rates (~10-4 s-1) and the results demonstrated that the BMG exhibited apparent uniform deformation initially, followed by visible local shear bands development. Afterwards, a single shear along the principal shear plane was soon developed and mainly dominated the whole deformation process. The principal shear contributed more than 2/3 of the overall plastic strain until failure. It was also found that the local shear strain varied along the principal shear plane and decreased monotonically from the shear band initiation site. Subsequently, in-situ compression experiments were conducted to monitor the change of sample shape during deformation in order to properly correlate with the stress-strain curve. The observed images showed that there was a one-to-one correspondence between the intermittent sample sliding and flow serration in the plastic region of stress-strain curve. Further investigations on flow serration were conducted on the Pd40Ni40P20 BMG through the compression experiments equipped with high-sensitivity strain gauges directly attached to two opposite sides of the test sample. There was an accompanied displacement burst when a shear band starts to propagate during deformation and this displacement burst would be accurately captured by the high-sensitivity strain gauges. Based on the displacement-time profile for one serration, shear-band propagating speed can be estimated and found to be insensitive to the applied strain rates (or the applied crosshead speeds). The disappearance of flow serration at high strain rates should be a result that the signal of displacement burst was overwhelmed by the applied strain rate. Using the shear strain rate data, the measured viscosity within a propagating shear band was found to be relatively low, which is in similar to the viscosity values reported in the supercooled liquid region during homogeneous deformation. In comparison with shear band propagation in the brittle Mg58Cu31Y6Nd5 and Au49Ag5.5Pd2.3Cu26.9Si16.3, moderately ductile Cu50Zr43Al7 and Pd40Ni40P20, and highly ductile phased-separated Zr63.8Ni16.2Cu15Al5 systems, the ductility of BMGs appears to be closely related to the dynamics during shear band propagation. The more ductile in nature the metallic glass is, the slower the shear band propagating speed would become. We also made attempts to investigate the shear band propagation in the porous Mo particles reinforced Mg58Cu28.5Gd11Ag2.5 bulk metallic glass composites (BMGCs) with up to 10% compressive failure strain. It was found that flow serration was absent in the stress-strain curve. Using high-sensitivity strain gauges, no distinct displacement burst was detected in the displacement-time profile. The diappearance of flow serration for the current porous Mo particles reinforced Mg58Cu28.5Gd11Ag2.5 BMGC is apparently associated with the lack of long-range shear band propagagtion. By employing the approach of separating the homogeneous amorphous matrix into many individual compartments, only short-range shear band propgagation is possible in the current Mg-based BMGC. An effective free spacing considering the spacing between two porous Mo particles and porous Mo particle size was applied to interpret the development of shear band propagation and is a useful indicator for the design of BMGC with high ductility.

Ce travail de thèse considère les modes de déformations des verres métalliques produits sous différentes formes (verres massifs, rubans et particules). La déformation hétérogène dans des échantillons massifs de verres métalliques à base de zirconium est étudiée par microscopie électronique à balayage. Le dégagement rapide de l'énergie élastique stockée sous forme de chaleur lors de la déformation est responsable de la fusion locale observée dans les bandes de cisaillement. Le calcul du profil de température autour d'une bande par un modèle analytique est cohérent avec les observations morphologiques et les rapports d'apparition de nano-cristaux dans la zone déformée. La mise en forme par recuit des rubans de verres métalliques a été étudiée. L'étude aboutit à la mise en forme sans fragilisation des rubans appartenant à différentes compositions de systèmes d'alliages dit métal-métal et métal-métalloïde. Un processus de traitement thermique est suggéré pour assurer la redistribution des contraintes imposées avant l'intervention de la fragilité thermique. Un brevet industriel basé sur ces résultats a été conjointement déposé avec un grand fabriquant de montres mécaniques. De nouveaux matériaux composites d'alliages légers commerciaux à base de Mg et d'Al renforcés par des dispersions de particules de verres métalliques ont été réalisés sans porosité. Une amélioration très nette des propriétés mécaniques est obtenue. / This thesis features the two modes of deformation of metallic glasses produced under different forms (bulk, ribbons and particles). Inhomogeneous deformation in bulk samples is studied by scanning electron microscopy. Heat generated by elastic energy release during deformation is responsible for the melting observed in shear bands, and calculations using an analytical model of the temperature profile around a band are consistent with morphological observations and reports of appearance of nano-crystals in or next to deformed areas. Shaping by annealing glassy ribbons was carried out. The study presents successful shaping without embrittlement of ribbons of different metal-metal and metal-metalloid compositions of glassy systems. A heat treatment process is suggested for redistribution of applied stresses before the intervention of thermal embrittlement. A joint patent for exploiting the findings has been filed with a major producer of mechanical watches. Development of new strong and light composite materials by dispersing glassy particles in aluminum and magnesium based matrices is presented and significant improvement in mechanical properties is obtained.

In this work, the Shear Transformation Zone (STZ) dynamics model is adapted to capture the transitions between different regimes of flow serration in the deformation map of metallic glass. This was accomplished by scaling the STZ volume with a log-linear fit to the strain rate, and also adjusting the activation energy of an STZ with a log-linear fit to maintain constant yield strength at differing strain rates. Twelve simulations are run at each of six different strain rates ranging from 10-5 to 100 s-1, and statistics are collected on simulation behavior and shear band nucleation and propagation rates. The simulations show shear band nucleation has a positive correlation to strain rate, and shear band propagation has a negative correlation to strain rate. This shows that in STZ dynamics, the regime of reduced flow serration arises due to competing rates of nucleation and propagation, supporting the hypothesis proposed by Schuh. A positive correlation between critical shear band nucleus size and strain rate is proposed as an underlying cause of these rate dependencies.

Ce travail de thèse considère les modes de déformations des verres métalliques produits sous différentes formes (verres massifs, rubans et particules). La déformation hétérogène dans des échantillons massifs de verres métalliques à base de zirconium est étudiée par microscopie électronique à balayage. Le dégagement rapide de l'énergie élastique stockée sous forme de chaleur lors de la déformation est responsable de la fusion locale observée dans les bandes de cisaillement. Le calcul du profil de température autour d'une bande par un modèle analytique est cohérent avec les observations morphologiques et les rapports d'apparition de nano-cristaux dans la zone déformée. La mise en forme par recuit des rubans de verres métalliques a été étudiée. L'étude aboutit à la mise en forme sans fragilisation des rubans appartenant à différentes compositions de systèmes d'alliages dit métal-métal et métal-métalloïde. Un processus de traitement thermique est suggéré pour assurer la redistribution des contraintes imposées avant l'intervention de la fragilité thermique. Un brevet industriel basé sur ces résultats a été conjointement déposé avec un grand fabriquant de montres mécaniques. De nouveaux matériaux composites d'alliages légers commerciaux à base de Mg et d'Al renforcés par des dispersions de particules de verres métalliques ont été réalisés sans porosité. Une amélioration très nette des propriétés mécaniques est obtenue.

Ce travail de thèse considère les modes de déformations des verres métalliques produits sous différentes formes (verres massifs, rubans et particules). La déformation hétérogène dans des échantillons massifs de verres métalliques à base de zirconium est étudiée par microscopie électronique à balayage. Le dégagement rapide de l'énergie élastique stockée sous forme de chaleur lors de la déformation est responsable de la fusion locale observée dans les bandes de cisaillement. Le calcul du profil de température autour d'une bande par un modèle analytique est cohérent avec les observations morphologiques et les rapports d'apparition de nano-cristaux dans la zone déformée. La mise en forme par recuit des rubans de verres métalliques a été étudiée. L'étude aboutit à la mise en forme sans fragilisation des rubans appartenant à différentes compositions de systèmes d'alliages dit métal-métal et métal-métalloïde. Un processus de traitement thermique est suggéré pour assurer la redistribution des contraintes imposées avant l'intervention de la fragilité thermique. Un brevet industriel basé sur ces résultats a été conjointement déposé avec un grand fabriquant de montres mécaniques. De nouveaux matériaux composites d'alliages légers commerciaux à base de Mg et d'Al renforcés par des dispersions de particules de verres métalliques ont été réalisés sans porosité. Une amélioration très nette des propriétés mécaniques est obtenue.

A key question in developmental biology is how form is generated. The model species Arabidopsis thaliana produces simple leaves with marginal outgrowths termed serrations. Serration development in A. thaliana requires both the transcription factor CUP-SHAPED COTYLEDON2 (CUC2) and the auxin efflux facilitator PIN-FORMED1 (PIN1), which regulates polar auxin transport by forming convergence points (Hay et al., 2006; Nikovics et al., 2006; Scarpella et al., 2006). In Chapter 3, I investigate how CUC2, PIN1 and auxin interact to control serration development. I demonstrate that CUC2 promotes PIN1 convergence point and auxin activity foci formation along the margin of the leaf, whilst high auxin activity represses CUC2 expression. Furthermore, interspersed peaks of CUC2 and auxin activity pattern serration development along the proximo-distal axis of the leaf. Thus, auxin, PIN1 and CUC2 form a negative feedback loop that patterns serration development. CUC genes and PIN1 are required for leaflet development in Cardamine hirsuta (Barkoulas et al., 2008; Blein et al., 2008), a close relative of A. thaliana that produces compound leaves subdivided into units termed leaflets. However, it is unclear how CUC and PIN1 interact to control leaflet development. In Chapter 4, I demonstrate that similar to A. thaliana, CUC genes promote PIN1 convergence point and auxin activity foci formation at the C. hirsuta leaf margin, whilst high auxin activity represses CUC2 expression. These genetic interactions likely create interspersed peaks of CUC2 and auxin activity that pattern leaflet development. Thus, the same negative feedback loop between CUC, PIN1 and auxin patterns both leaflet development in C. hirsuta and serration development in A. thaliana. KNOTTED1-LIKE HOMEOBOX (KNOX) genes are expressed in C. hirsuta leaves, and interact with ChCUC and PIN1 in positive and negative feedback loops, respectively, to control leaflet development (Barkoulas et al., 2008; Blein et al., 2008). KNOX genes are not expressed in A. thaliana leaves, but deeply lobed margins reminiscent of leaflets develop in association with ectopic KNOX expression in leaves (Chuck et al., 1996; Hay et al., 2006). However, it is unclear whether regulatory interactions of PIN1, CUC and KNOX which occur in C. hirsuta leaflets are employed during KNOX-induced lobe development in A. thaliana. In Chapter 5, I demonstrate that CUC2 and polar auxin transport are required for ectopic KNOX expression. Conversely, I show that KNOX misexpression up-regulates CUC2 expression in A. thaliana leaves. Thus, interactions between KNOX, CUC and PIN1 that occur in leaflet development in C. hirsuta also occur in association with KNOX-induced lobe development in A. thaliana. In addition to investigating the regulatory interactions between known components of leaf development pathways, I sought to identify novel genes that mediate CUC2-dependent serration development in A. thaliana. In Chapter 6, I identify a suppressor of the smooth margin phenotype of cuc2 leaves that partially restores PIN1 localisation in the absence of functional CUC2. Finally, in the General Discussion I evaluate how interlinking feedback loops between CUC, KNOX and auxin pattern serration and leaflet development. I then discuss why interlinking feedback loops may have been deployed to control outgrowths in both plant and animal systems.