Mechanical Testing of Micron and Sub-Micron Samples Using In-Situ Electron Microscopy

The size affected strength of metallic samples with micron and sub-micron dimensions has attracted considerable interest in the last few years [1]. While there are generally accepted trends on increasing strength with reduced specimen dimensions, 'smaller is stronger', the underlying mechanisms governing the improved yield strength and hardening behavior are still under debate. To identify the governing deformation mechanisms, we have developed setups to perform quantitative mechanical tests in-situ in electron microscopes, being either scanning electron microscopes (SEM) for micron sized samples, or a transmission electron microscope (TEM) for specimens down to dimension of only several tens of nanometers. The applications extend the common nanoindentation technique, where a multi-axial stress state under the indenter tip complicates the determination of a flow curve, to uni-axial quasi-static experiments in compression, tension, and bending, where the stress-strain curve is directly measured. But also dynamical testing such as low cycle fatigue experiments are possible. Since all the experiments are directly monitored in-situ in the electron microscopes, the emergence of slip steps [2] or the operation of individual dislocation sources [3] can be correlated to the mechanical sample response [4]. Such observations of deformation mechanisms are key ingredients to formulate mechanism based constitutive models that can describe the stochastic nature of metal deformation on a micron and sub-micron scale.