Nanostructures in austenitic steel after EDM and pulsed electron beam irradiation

Abstract

The resulting recast layer from EDM often exhibits high levels of residual stress, unacceptable crack density and high surface roughness; all of which will contribute to diminished surface integrity and reduced fatigue life. Previous studies have shown that the surface of EDM'd components can be successfully enhanced through the use of large-area pulsed electron beam surface modification, which, through a rapid remelting process, results in a net smoothing of the workpiece surface. It has also been shown that cracks created by EDM are repaired within the region molten by EB irradiation, and therefore the process is proposed to reduce the impact of EDM on fatigue life and deleterious surface properties. In this work the complex multilayers of the near surface are interrogated by TEM and XRD. A FIB-TEM study of the entire remelted layer produced by the irradiation process has been performed for the first time. The characterisation of these layers is necessary for predicting the performance of the material in application. Pulsed EB irradiation was shown to be capable of creating several distinct surface layers of nanostructures which consist of varying grain sizes and grain orientations. Austenite was revealed as the dominant phase in the remelted layer, with a grain size as small as 5 nm produced at the very top surface. A needle-like phase also present in the layer is thought to be cementite.

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