TY - THES

T1 - Fracture behavior of a tough bulk metallic glass at micrometer dimensions

AU - Jelinek, Alexander

N1 - embargoed until null

PY - 2020

Y1 - 2020

N2 - Metallic glasses are a relatively new class of materials, compared with conventional metals such as steel or aluminum. Since their discovery about 50 years ago, advances in the manufacturing process of metallic glass, together with deeper understanding of deformation mechanisms in amorphous materials, enabled the fabrication of bulk metallic glasses (BMGs), which may find broader application as structural materials in the future. Beside consistent limitations in production size they show an extraordinary combination of favorable properties. High hardness and elastic limit, together with high Young's modulus, corrosion resistance and glass specific traits makes them suitable for applications in micro- and nano-electro-mechanical-systems. Despite a lot of research is performed on BMGs, little data is present for mechanical properties at the micrometer size regime, as required for the above usage. While all glasses suffer from shear localization, leading to macroscopic brittle behavior, inherently ductile glasses exist, which show extraordinary high resistance to crack propagation. Furthermore, the applicability of conventional standards for the evaluation of miniaturized fracture toughness tests, with associated considerations regarding dimensions and testing condition, is still under scientific discussion. Further, the fundamental understanding of plasticity, realized trough the amorphous structure in metallic glasses, is an active topic in materials research. Therefore, this work strives for a deeper insight into the deformation mechanism and fracture behavior of a strong and ductile BMG, namely Pd77.5Cu6Si16.5. Multiple notched micro-mechanical samples in the shape of cantilevers were prepared by focused ion beam milling with different sizes and tested in-situ in a scanning electron microscope to observe the fracturing process. The specimens showed excessive blunting, elastic-plastic fracture mechanic concepts are applied. Since, standardized models could not provide significant values in terms of fracture toughness due to a lack of crack propagation, a model based on the deformation behavior of BMG at bending load is presented to rationalize the experimental results. This work shows, that some BMGs can exhibit extremely crack resistant behavior in small dimensions, making them suitable materials for sensing or actuator applications.

AB - Metallic glasses are a relatively new class of materials, compared with conventional metals such as steel or aluminum. Since their discovery about 50 years ago, advances in the manufacturing process of metallic glass, together with deeper understanding of deformation mechanisms in amorphous materials, enabled the fabrication of bulk metallic glasses (BMGs), which may find broader application as structural materials in the future. Beside consistent limitations in production size they show an extraordinary combination of favorable properties. High hardness and elastic limit, together with high Young's modulus, corrosion resistance and glass specific traits makes them suitable for applications in micro- and nano-electro-mechanical-systems. Despite a lot of research is performed on BMGs, little data is present for mechanical properties at the micrometer size regime, as required for the above usage. While all glasses suffer from shear localization, leading to macroscopic brittle behavior, inherently ductile glasses exist, which show extraordinary high resistance to crack propagation. Furthermore, the applicability of conventional standards for the evaluation of miniaturized fracture toughness tests, with associated considerations regarding dimensions and testing condition, is still under scientific discussion. Further, the fundamental understanding of plasticity, realized trough the amorphous structure in metallic glasses, is an active topic in materials research. Therefore, this work strives for a deeper insight into the deformation mechanism and fracture behavior of a strong and ductile BMG, namely Pd77.5Cu6Si16.5. Multiple notched micro-mechanical samples in the shape of cantilevers were prepared by focused ion beam milling with different sizes and tested in-situ in a scanning electron microscope to observe the fracturing process. The specimens showed excessive blunting, elastic-plastic fracture mechanic concepts are applied. Since, standardized models could not provide significant values in terms of fracture toughness due to a lack of crack propagation, a model based on the deformation behavior of BMG at bending load is presented to rationalize the experimental results. This work shows, that some BMGs can exhibit extremely crack resistant behavior in small dimensions, making them suitable materials for sensing or actuator applications.

KW - Bruchverhalten

KW - massives metallisches Glas

KW - Mikromechanik

KW - fracture behavior

KW - bulk metallic glass

KW - micro mechanics

M3 - Master's Thesis

ER -