Dynamic studies of the deformation & fracture of pearlite using 200 Kv SEM

Abstract

A Jeol 200 kV STEM equipped with a tensile deformation stage, a secondaray electron detector and a video recording chain has been used as a high voltage SEM to study in situ the deformation and fracture of miniature tensile specimens of pearlite. The advantage with high voltage SEM is that the increased gun brightness, compared with conventional SEMs, provides an improvement in resolution for a given signal/noise ratio and therefore allows higher magnifications to be used during the recording of dynamic deformation sequences at TV scanning rates. This facility proved to be essential for the TV monitoring of pearlites at the finest interlamellar spacings. The influence of interlamellar spacing on the mechanisms of deformation was of particular interest in this study and the materials examined ranged from coarse pearlite, with a mean interlamellar spacing λ ⁓ 0.4 μm, to fine pearlite with λ ⁓ 0.1 μm,. The problems of ex post facto reasoning regarding the modes of deformation were avoided by continuously following deformation with the TV monitor and recording high resolution slow scan micrographs from the same area both before and after straining.