Date

2021-8

Author

Bagheri Behboud, Ali

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Metallic glasses are metallic alloys with disordered atomic structures and desirable mechanical properties such as high hardness, high elastic limits, and wear resistance. These properties make metallic glasses promising materials for wear-resistant, corrosion-resistant, and biocompatible coating applications. On the other hand, metallic glasses are brittle, which is a major disadvantage for their use in practice. This thesis study aimed to tackle this problem through the development of nanostructured metallic glasses with high toughness and ductility. In the first part, the thesis considered synthesizing a binary thin film metallic glass over a wide compositional range. Two binary systems, namely, ZrTa and CuTa were investigated. Physical vapor deposition method was the approach for producing the thin films samples, and a combinatorial sputtering technique was employed during the deposition process. This way, 25 monolithic samples (13 ZrTa and 12 CuTa samples) were produced in only two sputtering sessions. The microstructures of the alloy systems were then investigated, demonstrating a wide compositional range of amorphous structures in both systems. Combining these with micromechanical testing provided the underlying structure-property relationships. The next step was the exploration of a novel approach for overcoming the brittle nature of metallic glasses through engineered heterogeneities in the form of compositional modulations. A recently developed indentation-based energy method was used to determine the fracture toughness of nanolayered ZrTa samples, and the results demonstrated that the nanolayered metallic glass composites combine high hardness with ductility, rendering this approach promising for the development of commercial coatings for engineering applications. The same route was also explored CuTa system. In this case, a more sophisticated technique was used to measure the ductility through direct tensile testing. The results showed that the nanolayered metallic glass and MG-crystalline composites combine high hardness, elastic modulus, and ductility, demonstrating their great potential to develop high performance composite coatings.

Subject Keywords

metallic glasses, thin films, fracture toughness, mechanical properties, nanostructured materials

URI

https://hdl.handle.net/11511/91695

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Graduate School of Natural and Applied Sciences, Thesis