Abstract
The need to understand the complex behaviors and properties of thin films has made their research an important field in materials science in recent years. Since their mechanical characteristics are so important in determining their usability in a wide range of possible applications, a great deal of study has been dedicated to clarifying them. This calls for a thorough investigation of how they behave in various loading scenarios, including compression, tension, and bending. Moreover, a complex interaction of characteristics such as composition, layer thickness, and deposition parameters has a significant effect on mechanical properties.One of the main forces behind materials development is the growing need for highly specialized coatings that are suitable for specific industrial applications. The main goal is to empower different sectors by providing customizable coatings that are specifically tailored to their own operating circumstances and requirements. Our study started a thorough investigation with the goal of developing a methodical approach to coating customization, which would go beyond the traditional trial-and-error method, in answer to this critical need.
Despite its crucial significance, fracture—a major failure mode—has surprisingly received comparatively little attention in previous coatings-related research. This thesis thus focuses on coating modification, with special attention to the fracture behavior of two different coating groups.
The first part of this study is to improve our understanding of the mechanical properties of amorphous carbon coatings. Using fracture energy, strength, and stiffness performance indices as primary evaluators, the research carefully adjusts deposition parameters such as bias voltage and deposition pressure. The objective is to engineer coatings exhibiting a targeted critical energy release rate spanning from 5 to 125 J/m² while preserving desirable yield strength (σy) (1.6-2.7 GPa) and elastic limits (σy⁄E՛ ) (approximately 0.05) with the tensile strain range between 0.003 and 0.15.
The subsequent phase of this research scrutinizes the fracture behavior of Cu-Zr thin film metallic glasses (TFMGs). Here, through a methodical examination of experimental evidence and meticulous analysis, previously overlooked fracture characteristics are uncovered. Intriguingly, the revelation that even a small amount of oxygen content (as low as 3-4 at.%) during the production of pure metallic glass (MG) films significantly impacts fracture behavior underscores the paramount importance of oxygen content in shaping fracture features.
This Ph.D. thesis aims to further the domains of materials science and surface engineering by providing new insights into the fracture characteristics of amorphous coatings based on amorphous carbon and metallic glasses. The development of high-performance coatings with modifiable mechanical characteristics and a better comprehension of their fracture behavior under various circumstances might benefit greatly from these findings.
| Date of Award | 16 Feb 2024 |
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| Original language | English |
| Awarding Institution |
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| Sponsors | PDR-FNRS |
| Supervisor | Stephane Lucas (Supervisor), Robert Sporken (President), Thomas Pardoen (Jury), Andreas Pflug (Jury), Philippe Steyer (Jury) & Matteo Ghidelli (Jury) |