Les verres métalliques sont des matériaux récents. Développés depuis les années 60, ils sont connus pour leur haute résistance mécanique et leur capacité à devenir visqueux à relativement basse température. La fonctionnalisation de leur surface est un moyen prometteur d’amélioration et d’optimisation de leurs propriétés. Cependant, la structure amorphe de ces matériaux est métastable et un maintien à une température trop élevée conduit systématiquement à la cristallisation du matériau et donc à une perte de ces propriétés uniques. La plupart des techniques de traitement de surface étant réalisées à hautes températures, elles ne sont pas adaptées à ce type de matériaux. Dans ce travail, deux techniques innovantes que sont le thermoformage et le traitement laser à impulsion ultra-courtes sont utilisées, permettant une texturation de la surface des verres métalliques tout en évitant la cristallisation. Cette thèse porte donc sur l’effet de ces deux traitements de surfaces sur les propriétés physico-chimiques de verres métalliques base zirconium et donc sur la modification de leur propriétés de surface telles que la mouillabilité ou la résistance à la corrosion. Nous verrons que ces deux techniques présentent chacune leur avantages et peuvent être particulièrement adaptées dans le cadre d’applications biomédicales. / Metallic glasses are recent materials. First developed in the 60s, they are well-known for their high mechanical resistance and their ability to become viscous at relatively low temperatures. Functionalization of their surfaces is a promising way to further increase their properties. However, their amorphous structure is in a metastable state and maintaining them at too high temperatures leads systematically to their crystallization, and thus the loss of their unique properties. Most of surface treatment techniques are performed at high temperatures and thus are not adapted to these materials. In this work, two innovative techniques which are thermoforming and ultra-short pulse duration laser treatment have been used and allow to texture the surfaces of the alloys by avoiding their crystallization. This thesis is focused on the effect of these two processing techniques on physical and chemical properties of Zr-based bulk metallic glasses and thus on the modification of their surface properties such as wettability or corrosion resistance. We will see that both techniques present their advantages and can be particularly adapted for biomedical applications.

abstract: Nanocrystalline (nc) thin films exhibit a wide range of enhanced mechanical properties compared to their coarse-grained counterparts. Furthermore, the mechanical behavior and microstructure of nc films is intimately related. Thus, precise control of the size, aspect ratio and spatial distribution of grains can enable the synthesis of thin films with exceptional mechanical properties. However, conventional bottom-up techniques for synthesizing thin films are incapable of achieving the microstructural control required to explicitly tune their properties. This dissertation focuses on developing a novel technique to synthesize metallic alloy thin films with precisely controlled microstructures and subsequently characterizing their mechanical properties using in situ transmission electron microscopy (TEM). Control over the grain size and distribution was achieved by controlling the recrystallization process of amorphous films by the use of thin crystalline seed layers. The novel technique was used to manipulate the microstructure of structural (TiAl) and functional (NiTi) thin films thereby exhibiting its capability and versatility. Following the synthesis of thin films with tailored microstructures, in situ TEM techniques were employed to probe their mechanical properties. Firstly, a novel technique was developed to measure local atomic level elastic strains in metallic glass thin films during in situ TEM straining. This technique was used to detect structural changes and anelastic deformation in metallic glass thin films. Finally, as the electron beam (e-beam) in TEMs is known to cause radiation damage to specimen, systematic experiments were carried out to quantify the effect of the e-beam on the stress-strain response of nc metals. Experiments conducted on Al and Au films revealed that the e-beam enhances dislocation activity leading to stress relaxation. / Dissertation/Thesis / Supplementary Video S1 / Supplementary Video S2 / Supplementary Video S3 / Doctoral Dissertation Materials Science and Engineering 2017

Vidros metálicos maciços fazem parte de um novo grupo de materiais de características distintas das ligas metálicas convencionais. O processamento dessas ligas ainda não foi bem consolidado nos centros de pesquisa brasileiros devido à dificuldade de processamento. Este trabalho descreve o desenvolvimento de um sistema de síntese e coquilhamento para a obtenção de vidros metálicos maciços. O sistema foi avaliado quanto ao desempenho e repetibilidade das amostras. A liga Cu46Zr42Al7Y5, formadora de vidro, foi processada e analisada através da caracterização por difração de raios-X (DRX), calorimetria exploratória diferencial (DSC) e microscopia eletrônica de varredura (MEV). Foram obtidas duas amostras com estrutura totalmente amorfa em espessuras médias de até 1,5 mm e uma amostra com aproximadamente 5,5 mm de espessura amorfa. A temperatura de transição vítrea observada foi igual às relatadas na literatura científica. Assim, o sistema desenvolvido mostrou-se eficiente para o controle da atmosfera, resfriamento rápido das amostras e outras variáveis que são obrigatórias para o sucesso na formação de estruturas amorfas em ligas por fundição. / Bulk metallic glasses are new materials with different features in comparison with conventional metallic alloys. The processing techniques of such alloys are still not consolidated in Brazilian research centers because of inherent processing difficulties. This work describes the development of a system for the synthesis and casting of bulk metallic glassy samples. The system was evaluated by its performance and alloys repeatability. The Cu46Zr42Al7Y5 alloy was processed and analyzed for the formation of amorphous structure through X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). It was produced two samples with fully amorphous structure at average thickness of 1.5 mm and one sample reaching around 5.5 mm of fully glassy structure. The same glass transition temperature reported on scientific literature was found in the alloys processed in the present work. Thus, the system has shown efficiency on atmosphere control, sample quenching and others important variables that are, by default, necessary to succeed in amorphous structure formation.

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A large set of experimental results obtained by the author and colleagues related to the diffusionrelated effects and phase transformation observed in metallic glasses will be presented and discussed.

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Metallic Glasses are multi-component alloys with disordered atomic structures and unique and attractive properties such as ultra-high strength, soft magnetism, and excellent corrosion/wear resistance. In addition, they may be thermoplastically processed in the supercooled liquid region to desired shapes across multiple length-scales. Recently developed metallic glasses based on noble metals (such as Pt and Pd) are highly active in catalytic reactions such as hydrogen oxidation, oxygen reduction, and degradation of organic chemicals for environmental remediation. However, there is a limited understanding of the underlying electrochemical mechanisms and surface characteristics of catalytically active metallic glasses. Here, we demonstrate the influence of alloy chemistry and the associated electronic structure on the activity of a systematic series of Pt42.5−xPdxCu27Ni9.5P21 bulk metallic glasses (BMGs) with x = 0 to 42.5 at%. The activity and electrochemically active surface area as a function of composition are in the form of volcano plots, with a peak around an equal proportion of Pt and Pd. These amorphous alloys showed more than two times the hydrogen oxidation reactivity compared to pure Pt. This high activity was attributed to their lower electron work function and higher binding energy of Pt core level that reduced charge-transfer resistance and improved electrocatalytic activity from weakened chemisorption of protons. To address the high cost associated with noble-metal-based amorphous catalysts, the performance of non-noble M100-xPx alloys was evaluated with a systematic variation in chemistry (M = Ni, Co; x = 0, 10, 15, 20, 30 at%). These alloys were synthesized by a scalable pulsed electrodeposition approach with glass formation seen in the range of 10 at% to 20 at% P. Enhanced corrosion resistance was observed with increasing phosphorus content as evidenced by the significant decrease in corrosion current density and ten-fold higher polarization resistance of M80P20 (M = Ni, Co) compared to its corresponding pure metal in representative electrolytes. Surface characterization showed enrichment of phosphorus in the passive layer, that likely promoted the restoration of the protective hypophosphite phase. The overpotential for hydrogen evolution reaction decreased by 35% and 45% in the case of Ni100−xPx and Co100−xPx, respectively, with increasing phosphorus content from 0 at% to 20 at%. Also, the M80P20 (M = Ni, Co) metallic glasses demonstrated excellent oxygen evolution reaction efficiency with a 10 mA/cm2 current density at 50% overpotential compared to pure Pt in alkaline media. The high activity and excellent durability of the non-noble amorphous alloys for hydrogen/oxygen evolution reactions (HER/OER) were attributed to the decreased binding energy of the P core level due to the synergy between the proton-acceptor (P centers) and hydride/hydroxide-acceptor (metal centers) sites.

Hong Sin Yi, Grace. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 50-51). / Acknowledgments / Abstract / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Metallic Glass and its application --- p.1 / Chapter 1.2 --- Glass Forming Ability (GFA) --- p.2 / Chapter 1.3 --- Equilibrium Phase --- p.3 / Chapter 1.4 --- Nucleation and Growth --- p.6 / Chapter 1.5 --- Spinodal Decomposition --- p.8 / Chapter 1.6 --- Morphology Comparison between Nucleation and Growth and Spinodal --- p.13 / Figures --- p.14 / References --- p.24 / Chapter Chapter 2 --- Experimental Method / Experimental Method --- p.25 / Figure --- p.29 / References --- p.30 / Chapter Chapter 3 --- Metastable liquid miscibility gap in Pd-Si and its glass forming ability / Introduction --- p.32 / Experimental --- p.33 / Results --- p.34 / Discussion --- p.36 / Figures --- p.40 / References --- p.49 / Bibliography --- p.50