Precession Electron Diffraction based TEM Studies of Microstructure Evolution in Severely Plastically Deformed Austenitic Stainless Steel

Austenitic stainless steels offer good property combinations for structural component applications in demanding and aggressive environments, including nuclear power plants, where irradiation assisted degradation failures have been reported [1]. Enhanced irradiation tolerance has been reported for materials containing a high density of internal interfaces that act as point defect annihilation or sink sites [2]. Utilizing methods of severe plastic deformation (SPD) grain refinement in austenitic stainless steels to the sub-micron and nanometer scale have been reported [3]. Establishing quantitatively relationships between processing parameters, microstructrual metrics (e.g. grain size, internal strain, grain boundary character distributions and texture) and properties of strongly grain refined bulk polycrystalline aggregate materials after SPD requires experimental tools with nanometer spatial resolution that can deliver statistically significant and representative data sets. SPD typically results in non-equilibrium microstructures, typically containing significant cold-deformation strain, excess defect density in grain interiors and in the grain boundaries, while also exhibiting down to nanometer scale refined grain size [3]. Due to the combined effects of these characteristics ascertaining respective microstructural metrics, e.g. grain size, by conventional methods based on X-ray diffraction (XRD), scanning electron microscopy (SEM) electron backscatter diffraction based (EBSD) orientation imaging microscopy (OIM) or diffraction contrast transmission electron microscopy (TEM) imaging often proves difficult.