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

An in-situ nanomechanical cooling system has been developed to study the temperature dependency of local mechanical properties and slip behavior of bcc alpha-Fe. Uniaxial compression tests with Focused Ion Beam (FIB) fabricated pillars with a diameter of 1 am, were performed in the single slip orientations [(2) over bar 35] and [(1) over bar 49] at room temperature and 198 K. 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) over bar 35] pillars at both room temperature and 198 K while the predominantly slip systems governing the deformation on [(1) over bar 49] pillars were {110} < 111 > for both test temperatures. The stress-strain response showed an increased strength with decreasing temperature for the [(2) over bar 35] pillars, in contrast to [(1) over bar 49] pillars, where only a weak temperature dependence is observed. Furthermore, for [(2) over bar 35] pillars, the appearance of slip is less prominent at 198 K, indicating that the temperature strongly influences the relative motion of screw and edge dislocations. Molecular Dynamics (MD) simulations performed at 15 K and 300 K, was used to study dislocation mechanisms for the two orientations. [(1) over bar 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.