High resolution-digital image correlation techniques to assess slip events

International audienceIn polycrystalline metallic materials, assessment of the plasticity in relation to the microstructure is necessary to understand the deformation processes during mechanical loading. High resolution digital image correlation (HR-DIC) techniques coupled with novel DIC codes have emerged as a quantitative tool to assess heterogeneous strain field at the microscale. In-situ and ex-situ scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM) tensile testing were developed to characterize the continuous and discrete kinematics fields at the sub-grain level associated with non-localized deformation and slip events at room temperature. In-situ HR-DIC under SEM was capable to evidence elastic anisotropy of nickel-based superalloys at the grain scale. When irreversible deformation is concerned, {111}<110> slip systems identification using in-plane HR-DIC under SEM was possible. HR-DIC under LSCM added the possibility to measure the out-of-plane displacements and to fully quantify the slip activity, i.e. the local shear strain induced by individual slip bands.The validation of the HR-DIC technique at room temperature prompted its application at temperatures representative of service conditions for polycrystalline nickel-based superalloys. Ex-situ intermediate temperature HR-DIC tests under SEM were thus conducted to evaluate the local slip activity under macroscopic cyclic deformation in reactive atmosphere. Local oxide spikes were found to form under cyclic loading in grains where plastic deformation was observed to occur in the first cycles.HR-DIC clearly demonstrates the synergy existing between local slip activity at the microstructure scale and environment induced surface degradation