In-situ Transmission Electron Microscopic Nanomechanical Investigations of Ni

Date: 17 December 2018

Venue: Campus Groenenborger, U0.25 - Groenenborgerlaan 171 - 2020 Antwerpen (route: UAntwerpen, Campus Groenenborger)

Time: 4:00 PM

Organization / co-organization: Department of Physics

PhD candidate: Vahid Samaee

Principal investigator: D. Schryvers & H. Idrissi

Short description: PhD defence Vahid Samaee - Faculty of Science, Department of Physics


Nano- and micro-scale materials are used in various technologies such as microelectronics and micro-electro-mechanical systems. In these applications, small sized materials are subjected to external and internal stresses that can affect their integrity. However, although nanomechanical testing now has enabled the investigation of mechanical properties of these systems, the interpretation of the results and proposed mechanisms at small-scales are still under discussion. For instance, both steady and intermittent plastic flow has been observed in single crystals micro-scale samples, and the exact nature of the mechanisms underlying the mechanical properties is still unclear.

Furthermore, nanomechanical testing gives the chance to tackle old questions such as the role of interfaces in the mechanical properties in quantitative manner. In the present thesis, a novel sample preparation method is introduced allowing preparing “clean” nano-scale tensile test samples proper for quantitative in-situ TEM testing. Furthermore, advanced scanning and transmission electron microscopy including in-situ micro/nanomechanical testing techniques have been used to unravel the elementary deformation mechanisms in micron sized single and bi-crystal Ni samples.

The results revealed the role of FIB-induced damages in the deformation of small-scale samples, the role of geometrical changes due to the operation of a single arm dislocation source on the mechanical response of small-scale samples, the plausible interactions of different types of dislocations and a coherent twin boundary, and the role of the mean free path of dislocations in the formation of dislocation walls.