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In this study, Mg-Cu thin film metallic thin films were fabricated via two ways, the co-deposition and post-annealing of the multilayered thin films. Amorphous Mg1-xCux, where x is from 38 to 82, thin films with nanocrystalline particles are able to be fabricated via co-sputtering. The mechanism of formation is different from the rapid quenching process. For the Mg-Cu co-sputtering system, the mechanical properties of the Mg-Cu co-sputtered films were tested via MTS nanoindenter. Mg23.5Cu76.5 exhibits a higher Young¡¦s modulus than Mg17.7Cu82.3 and Mg40.4Cu59.6 due to the partial amorphous structure. Moreover, the pop-in effects with a smaller size occurs of the Mg23.5Cu76.5 sample in a higher frequency than of the Mg17.7Cu82.3 and Mg40.4Cu59.6 samples. The small pop-in effects in the Mg23.5Cu76.5 sample approximate match the width of amorphous matrix via the HRTEM observation. Another process to form the amorphous thin film is via the post isothermal annealing process of the multilayered thin films. However, for the specimens of 20T32 consisting of 150-nm Mg and 50-nm Cu individual layers, the Mg individual layers would react to the Cu individual layers during the annealing at a temperature of 413 K owning to the slight negative heat of mixing. Due to the localized diffusion near the interfaces, Mg2Cu gradually form during the isothermal annealing since Mg2Cu is the most stable phase below 548 K [62]. Localized interdiffusion near the interfaces between Mg and Cu individual layers induced the formation of Mg2Cu rapidly. For the 40T32 specimens consisting of 15 nm Mg and 5 nm Cu individual layers, Mg2Cu rapidly form at 413 K due to the high interface energy. Then, the similar result exhibits in the 20T14 and 40T14 specimens annealed at 363 K.

In this dissertation, the ternary Mg-based amorphous ribbons are characterized and analyzed first. Among the three Mg65Cu25Y10, Mg65Cu25Gd10 and Mg65Ni25Gd10 amorphous ribbons, the Mg65Cu25Gd10 amorphous ribbon exhibits the best thermal properties in terms of the glass forming ability (GFA) indexes, such as 68 K of the supercooled liquid region (£GTx), 29 K of the liquidus region (£GTl), 0.582 of the reduced glass transition temperature (Trg), 0.427 of the £^ value and 0.768 of the £^m value. In spite that the Mg65Cu25Gd10 amorphous ribbons do not show the best performance in mechanical properties, such as micro-hardness value of 231 Hv (2.26 GPa), nano-hardness value is 3.24 GPa (300 Hv) and modulus from nano-indentation of 62.4 GPa, this composition is close to the two prediction compositions of Mg62Cu27Gd11 (the e/a-variant criterion) and Mg67Cu23Gd10 (the binary eutectic clusters criterion). However, among a series of ternary of Mg-Cu-Gd amorphous ribbons, the better overall thermal properties are seen in the Mg54Cu32Gd14 and Mg54Cu31Gd15 amorphous ribbons. In terms of the bulk Mg65Cu25Gd10 amorphous alloys, the 6 mm bulk metallic glass (BMG) rod can be fabricated successfully with minimum porosity. In order to improve the brittle properties of the Mg65Cu25Gd10 BMG rod, there are two methods applied in this study, namely, the intrinsic toughening method by heat treatment and the extrinsic toughening method of adding reinforcements. For the heat treated Mg65Cu25Gd10 BMG rod, both of the one-step and two-steps BMG rods show no distinct plastic deformation in the engineering stress-strain curves, while the micro-hardness and compressive stress are increased from 270 Hv to higher than 300 Hv and from 804 to 830 MPa. But, for the ductile metal-reinforced Mg-based BMG rods, the brittle properties are improved. For the Nb-reinforced Mg65Cu25Gd10 BMG rods, the compressive stress decreases from 804 to 595 MPa and the plastic strain increases from 0 to 0.48% with increasing volume fraction from 0 to 17.3%. But, for Mg65Cu25Gd10 BMG rod reinforced by 21.6% porous Mo, the compressive stress and plastic strain are 821 MPa and 1.63%, respectively. Moreover, for the porous Mo-reinforced Mg58Cu28.5Gd11Ag2.5 BMG rods, the compressive stress increases from 827 to 1111 MPa and the plastic strain increases from 0 to 7.84% with increasing volume fraction from 0 to 25.4%.

The glass forming ability (GFA) of the lightweight Mg65Cu25Y10 alloy has been widely studied. This alloy contains a medium sized Mg matrix (0.16 nm in atomic radius), a small sized Cu (0.14 nm) and a large sized Y (0.18 nm). The glass transition temperature Tg, supercooled temperature range

Neste trabalho foi feito um estudo das propriedades estruturais e eletroquímicas de eletrodos formados por pó de liga de hidreto metálico Zr0,9Ti0,1Ni1,04Mn0,64V0,46 (tipo AB2) preparadas em forno a arco e tratadas por moagem em moinho de bolas na presença de pó de Ni ou da liga LaNi4,7Sn0,3. Também foram estudadas ligas à base de Mg-Ni preparadas por moagem de alta energia, com e sem a inclusão de um terceiro elemento (Ti ou Pt). Neste último caso, foi realizada deposição eletroquímica para o revestimento da superfície da liga Mg-Ni com paládio. Os estudos nos dois sistemas foram conduzidos utilizando-se as técnicas de EDX (energia dispersiva de raios X), DRX (difração de raios X) e MEV (microscopia eletrônica de varredura) para a caracterização física dos materiais. Também foram realizados experimentos espectroscopia de absorção de raios X (XAS) e de microscopia eletrônica de transmissão (MET). Os estudos eletroquímicos incluíram medidas da polarização dos eletrodos ao longo dos ciclos de carga/descarga, com o monitoramento da capacidade de descarga em função do número de ciclos. Medidas de espectroscopia de impedância eletroquímica em diferentes estado de carga, temperaturas e números de ciclos foram realizadas nos eletrodos formados com as diferentes ligas. Foi observado que a capacidade de armazenamento de carga da liga AB2 sem tratamento, aumenta muito lentamente com o decorrer do número de ciclos de carga/descarga, enquanto que os eletrodos formados com essa mesma liga, porém submetida aos tratamentos superficiais pela moagem com os diferentes aditivos, apresentam ativação muito mais rápida. Pelas medidas de impedância eletroquímica, observou-se alta similaridade da cinética reacional nas várias amostras AB2 analisadas. A substituição parcial da liga MgNi pela Pt levou à uma maior estabilidade aos ciclos de carga e descarga, inibindo a formação de hidróxido de Mg e proporcionando uma cinética tanto de absorção quanto de dessorção do hidreto maior que sua correspondente liga base. A eletrodeposição de Pd nestas ligas, leva à um incremento adicional na estabilidade do eletrodo. / This work reports results of studies on the structure and electrochemical properties of hydrogen storage alloy electrodes, formed by Zr0,9Ti0,1Ni1,04Mn0,64V0,46 (AB2-type), prepared in arc furnace and processed by ball milling in the presence of Ni and/or LaNi4,7Sn0,3 powder additives. The Mg- Ni based alloys with and without incorporation of Ti and Pt, processed by mechanical alloying were also investigated. In this case, electrochemical deposition of palladium was carried out on the surface of Mg-Ni based alloy particles aiming at improving the alloy stability. The structure of all materials were characterized by energy dispersive X-ray (EDS) analyses, X-ray diffraction (XRD) and scanning electronic microscopy (SEM). X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM) were also employed for this purpose. Electrochemical studies involved measurements of the electrode polarization along the charge/discharge cycles and also monitoring total discharge capacity as a function of the cycle number. Reaction kinetics were investigated by electrochemical impedance spectroscopy (EIS) measurements, conducted at different states of charge, temperatures and cycle numbers for the different metal hydride electrodes. It was found that the charge storage capacity increased very slowly along the initial charge/discharge cycles for the bare AB2 alloy, but a significant decrease of the activation time, due to a raise on the active area caused by the milling treatment was seen, independent of the additive nature. Electrochemical impedance showed similar reaction kinetics for different AB2 samples. The inclusion of small content of Pt in the Mg-Ni alloy leaded to a significant increase of the material stability for the charge/discharge cycles, probably because of a reduction in the corrosion processes. Consistently, the electrochemical coatings of Pd lead to a raise in the cycling stability of these alloys.

The thermal and mechanical properties of the Mg-based bulk metallic glasses are reported in this thesis. The original ingots were prepared by arc melting and induction melting. The thermal and mechanical properties of the Mg-based bulk metallic glasses are reported in this thesis. The original ingots were prepared by arc melting and induction melting. The Mg65Cu25Gd10 and Mg65Cu15Ag10Gd10 bulk metallic glasses with different diameters from 3 to 6 mm were successfully fabricated by conventional copper mold casting in an inert atmosphere. The Mg65Cu25Gd10 bulk metallic glass shows the high glass forming ability and good thermal stability. However, the addition of Ag in the Mg65Cu15Ag10Gd10 alloy degrades the thermal stability. Based on the DSC results, the supercooled liquid region

Neste trabalho foi feito um estudo das propriedades estruturais e eletroquímicas de eletrodos formados por pó de liga de hidreto metálico Zr0,9Ti0,1Ni1,04Mn0,64V0,46 (tipo AB2) preparadas em forno a arco e tratadas por moagem em moinho de bolas na presença de pó de Ni ou da liga LaNi4,7Sn0,3. Também foram estudadas ligas à base de Mg-Ni preparadas por moagem de alta energia, com e sem a inclusão de um terceiro elemento (Ti ou Pt). Neste último caso, foi realizada deposição eletroquímica para o revestimento da superfície da liga Mg-Ni com paládio. Os estudos nos dois sistemas foram conduzidos utilizando-se as técnicas de EDX (energia dispersiva de raios X), DRX (difração de raios X) e MEV (microscopia eletrônica de varredura) para a caracterização física dos materiais. Também foram realizados experimentos espectroscopia de absorção de raios X (XAS) e de microscopia eletrônica de transmissão (MET). Os estudos eletroquímicos incluíram medidas da polarização dos eletrodos ao longo dos ciclos de carga/descarga, com o monitoramento da capacidade de descarga em função do número de ciclos. Medidas de espectroscopia de impedância eletroquímica em diferentes estado de carga, temperaturas e números de ciclos foram realizadas nos eletrodos formados com as diferentes ligas. Foi observado que a capacidade de armazenamento de carga da liga AB2 sem tratamento, aumenta muito lentamente com o decorrer do número de ciclos de carga/descarga, enquanto que os eletrodos formados com essa mesma liga, porém submetida aos tratamentos superficiais pela moagem com os diferentes aditivos, apresentam ativação muito mais rápida. Pelas medidas de impedância eletroquímica, observou-se alta similaridade da cinética reacional nas várias amostras AB2 analisadas. A substituição parcial da liga MgNi pela Pt levou à uma maior estabilidade aos ciclos de carga e descarga, inibindo a formação de hidróxido de Mg e proporcionando uma cinética tanto de absorção quanto de dessorção do hidreto maior que sua correspondente liga base. A eletrodeposição de Pd nestas ligas, leva à um incremento adicional na estabilidade do eletrodo. / This work reports results of studies on the structure and electrochemical properties of hydrogen storage alloy electrodes, formed by Zr0,9Ti0,1Ni1,04Mn0,64V0,46 (AB2-type), prepared in arc furnace and processed by ball milling in the presence of Ni and/or LaNi4,7Sn0,3 powder additives. The Mg- Ni based alloys with and without incorporation of Ti and Pt, processed by mechanical alloying were also investigated. In this case, electrochemical deposition of palladium was carried out on the surface of Mg-Ni based alloy particles aiming at improving the alloy stability. The structure of all materials were characterized by energy dispersive X-ray (EDS) analyses, X-ray diffraction (XRD) and scanning electronic microscopy (SEM). X-ray absorption spectroscopy (XAS) and transmission electron microscopy (TEM) were also employed for this purpose. Electrochemical studies involved measurements of the electrode polarization along the charge/discharge cycles and also monitoring total discharge capacity as a function of the cycle number. Reaction kinetics were investigated by electrochemical impedance spectroscopy (EIS) measurements, conducted at different states of charge, temperatures and cycle numbers for the different metal hydride electrodes. It was found that the charge storage capacity increased very slowly along the initial charge/discharge cycles for the bare AB2 alloy, but a significant decrease of the activation time, due to a raise on the active area caused by the milling treatment was seen, independent of the additive nature. Electrochemical impedance showed similar reaction kinetics for different AB2 samples. The inclusion of small content of Pt in the Mg-Ni alloy leaded to a significant increase of the material stability for the charge/discharge cycles, probably because of a reduction in the corrosion processes. Consistently, the electrochemical coatings of Pd lead to a raise in the cycling stability of these alloys.

No description available.

Amorphous metals have been discovered in 1960 and, because of their structures, exhibit very unique mechanical, magnetic and chemical properties that can have various applications. These properties qualify them as the potential material of the future. This work focuses on a new laser ablation technique to synthesize nanoparticles of amorphous metals from aqueous feedstock. One of the critical factors in the production of amorphous metal is the cooling rate used to synthesize them. The laser ablation of microparticle aerosol (LAMA) process used in this work, with a cooling rate estimated of 10¹² K/s, has all the characteristics required for the production of such metallic glasses. A Collison nebulizer is used to generate microdroplets of a nitrate solution containing the corresponding ratio of metals for the production of a Zr-Al-Ni based alloy. Once dried and conditioned, these microdroplets leave solid microparticles which are ablated by an excimer laser producing nanoparticles that are then filtered by virtual impaction. In order to characterize the nanoparticles obtained with this process nanoparticulate films produced by LAMA have been analyzed by optical profilometry, scanning electron microscopy (SEM) equipped with energy-dispersive x-ray spectroscopy (EDS) and transmission electron microscopy (TEM) equipped with EDS. The results agree with a hypothesis that the films contain oxidized, amorphous metal on the surface of the films. When the films are thin, they are fully oxidized, and simultaneous segregation of Zr occurs to the surface. The hypothesis and the results are discussed. / text

No description available.