Plasticity and creep in thin free-standing nanocrystalline Pd films
(2014)
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- Abstract
- In the constant race towards miniaturization, the scientific community faces multiple challenges regarding the characterization and control of the mechanical performance and reliability of devices and materials at the smallest scales. Thin films are materials presenting one extremely reduced dimension, from a few microns down to a few nanometres. The reduced dimension proved to be at the origin of new and improved properties of thin films as compared with their bulk counterpart, as for instance an increased mechanical strength. But, other properties deteriorate with size reduction like ductility. The objective of this PhD thesis was to study the deformation and relaxation mechanisms in nanocrystalline palladium films of various thicknesses (between 80 and 500 nm) in relationship with the microstructure. The ambition was to characterize, understand, predict, and, finally, to propose routes to improve the mechanical properties. An on-chip microtensile testing approach was used for this purpose allowing the measurement of the response under uniaxial tension with or without relaxation. Coupled transmission electron microscopy studies have been performed in- or ex-situ to unravel the underlying mechanisms dictating the mechanical properties. The yield stress, the strain hardening, the ductility and the strain rate sensitivity parameters of Pd films with various configurations and deposition conditions (thickness, twin density, dislocation density, confinement, ageing, annealing) have been measured and related to the elementary deformation mechanisms. A semi-analytical grain aggregate model has been proposed to provide a quantitative link between the microstructure and properties. Finally, the effect of hydrogen on the mechanical response of the films has been explored.
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Citations
Colla, M.-S. (2014). Plasticity and creep in thin free-standing nanocrystalline Pd films. https://hdl.handle.net/2078.5/236805