Low temperature in-situ micro-compression testing of iron pillars

Abstract

An in-situ nanomechanical cooling system has been developed to study the temperature dependency of local mechanical properties and slip behavior of bcc α-Fe. Uniaxial compression tests with Focused Ion Beam (FIB) fabricated pillars with a diameter of 1µm, were performed in the single slip orientations 2¯35 and 1¯49 at room temperature and 198K. The testing was conducted inside a Scanning Electron Microscope (SEM) equipped with a nanoindenter. Slip trace analyses revealed occurrence of slip in the {112}<111> family of slip systems for 2¯35 pillars at both room temperature and 198K while the predominantly slip systems governing the deformation on 1¯49 pillars were {110}<111> for both test temperatures. The stress-strain response showed an increased strength with decreasing temperature for the 2¯35 pillars, in contrast to 1¯49 pillars, where only a weak temperature dependence is observed. Furthermore, for 2¯35 pillars, the appearance of slip is less prominent at 198K, indicating that the temperature strongly influences the relative motion of screw and edge dislocations. Molecular Dynamics (MD) simulations performed at 15K and 300K, was used to study dislocation mechanisms for the two orientations. 1¯49 pillars exhibit a change in deformation mechanisms at low temperature and the evolution of dislocation density during deformation, display distinct differences for the two loading orientations.