Seleção de ligas com alta tendência de formação de estrutura amorfa
Resumen
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.