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Seleção de ligas com alta tendência de formação de estrutura amorfa
(Universidade Federal de São Carlos, 2007-03-08) Aliaga, Luis César Rodriguez; Kiminami, Claudio Shyinti; https://lattes.cnpq.br/5443002033733395; https://lattes.cnpq.br/7148278938710201
The understanding of the law that explain why certain alloys form amorphous structure by cooling the molten melt under cooling rates lower than others alloys remains as one of the great challenges of the materials science and engineering. There is not only scientific but also technological importance in determining the best compositions that can form such metastable structures with larger simplicity. In an effort for elucidating part of this mystery diverse models and criteria are promising: i) of topological instability, "λ criterion", and ii) the thermodynamic approach, "γ* criterion". The application of this last one in binary systems showed excellent prediction of the amorphous former compositions. Although, experimental results through the years have proven that multi-component systems, especially ternary ones, are more suitable to form bulk samples with amorphous structure. The goal of this thesis is to search compositions with high glass forming ability, by means of the application of models and criterions focusing on systems based on chemical elements of relative low cost. An extension of the γ* criterion , for ternary systems, was developed and valided for Cu-Zr-Al alloys. That extension of the γ* criterion was, combined with the λ-criterion , applied to select new alloy compositions with high glass forming ability in Ni-Ti and Ni-Nb-B systems. The combined use of both criterions was quite powerful tool in the selection of alloys with the higher GFA.
Influência da ordem-desordem estrutural na fotoluminescência do CaTiO3:Sm
(Universidade Federal de São Carlos, 2007-03-08) Figueiredo, Alberthmeiry Teixeira de; Longo, Elson; https://lattes.cnpq.br/9848311210578810; https://lattes.cnpq.br/7026388762536003
Some properties of the materials, such as ferroelectric and optic, are dependents to structural organization of the material. Thus, to know the order disorder degree at short, intermediate and long range is important to elucidate or predict properties in materials. The PL emission at room temperature will be used to study the structural order disorder at short, intermediate and long range in the CaTiO3:Sm, in function of annealed temperature. Using studies of the structural order disorder in the CaTiO3:Sm system will propose a model that appoint to favorable conditions, in disordered material, to show PL emission at room temperature.