In-situ Laue diffraction on deforming micropillars

Single crystal deformation unveiling the characteristics of crystal glide and the role of defect propagation herein has been a matter of intense research more than 60 years ago. A manifold of different mechanical testing methods and crystal qualities were investigated to gain understanding in parameters that influence the mechanical response of macroscopic single crystals. It became clear at that time how sensitive the crystal's plastic flow behavior is to both intrinsic and extrinsic parameters, where the first relates to the initial perfection of the crystal and the latter pertains to mechanical effects arising from the testing environment. From these macroscopic single crystal deformation experiments, fundamental insights were gained on micromechanistical processes and spatial dynamics of the evolving dislocation structure. But how is a crystal behaving when its geometrical dimension shrinks towards the length scale of the internal dislocation structure? This question was hard to address at the golden age of single crystal research because of the difficulty in controlling micromechanical testing and the non-availability of small samples. Today we are steering towards a "nano-society". Sample preparation and instrumentation to perform such experiments are now routinely possible, which allows investigating the posed question. This is the context, in which the present work is to be placed. This dissertation presents data obtained with a unique and specially developed in situ micro compression device, designed to operate in combination with a micro focused polychromatic x-ray beam impinging on the microscopic single crystalline cylindrical sample (e.g. a pillar) that is to be deformed. The particular choice of combining micro compression and micro focused Laue diffraction was pursued to enable non-destructive probing of the deforming microcrystal, providing a step beyond micro compression alone. At the beginning of this thesis work, the still young literature on micro compression results revealed a large sample size-effect for the strength of microcrystals – as the external dimension decreases the strength was found to increase. Rationale for the geometrical size-effect of microcrystals has been debated, since strengthening interface-effects, as encountered in polycrystals, are absent in single crystals. New dislocation mechanisms were proposed to account for the size-effect. These models were established without knowing the evolution of the microstructure within the deforming crystals. A non-destructive experimental technique was needed to address this evolution. This demand was met by the unique combination of micro compression and micro diffraction, and constitutes a pioneering effort to investigate small scale plasticity by means of Laue diffraction as a function of strain. The results of this thesis work provide an in situ view on the small scale plasticity occurring in micro crystals that is richer than that derived from mechanical testing a