Novas ligas formadoras de fase amorfa do sistema Ni-Nb-Zr e seu comportamento mecânico

• Autor(a) principal: Santos, Fabricio Simão dos
• Data de Publicação: 2011
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da UFSCAR
• Texto Completo: https://repositorio.ufscar.br/handle/ufscar/679
• topic: Metalurgia; Metais amorfos; Vidros metálicos; Nanoindentação; ENGENHARIAS

Ni-based amorphizable alloys in the bulk form show a good combination of properties, with high mechanical strength and hardness, good ductility and excellent corrosion resistance. These alloys have been used in recent technological applications, for example, in pressure sensors and micro-geared motors. Particularly, Ni-Nb-Zr alloys with amorphous structure show, in addition to good mechanical properties, excellent corrosion resistance in acid medium due to the formation of a Nb- and Zr-rich passive film. In this context, the purpose of this project is to develop Ni-Nb-Zr alloys with high glass-forming ability (GFA) by using the topological &#955; criterion combined with the average electronegativity difference, &#916;e , and to carry out its mechanical characterization by nanoindentation. Ni45.5Nb23Zr31.5, Ni50Nb28Zr22, Ni57Nb17.5Zr25.5 and Ni79Nb8.5Zr12.5 alloys were selected and produced in the form of melt-spun ribbons and copper mold cast wedges. The samples were analyzed by inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and nanoindentation. Results from the processing of wedge samples revealed the highest GFA for the Ni50Nb28Zr22 alloy, which presented 60% of amorphous fraction for a thickness of 200 &#956;m and 23% for thickness of 320-480 &#956;m. The alloy Ni45.5Nb23Zr31.5 showed the second highest GFA, making possible to obtain 14% of amorphous fraction for a thickness of 240 &#956;m. The hardness and reduced elastic modulus of the ribbon samples increased in the following order: Ni45.5Nb23Zr31.5 < Ni50Nb28Zr22 < Ni57Nb17.5Zr25.5. For the Ni50Nb28Zr22 alloy, it was attained higher hardness and elastic modulus and lower plastic energy for the wedge compared to the ribbon, which can be ascribed to the higher amount of free volume in the structure of the amorphous ribbon. The compressive yield stress (&#963;y,C) of this alloy was estimated to be 2.5 and 3.2 GPa for ribbon and wedge, respectively. viii