Formation of large grains by epitaxial and abnormal growth at the surface of pulsed electron beam treated metallic samples

Abstract

The aim of the present work was to clarify that the rapid solidification process involved during surface pulsed beam treatment does not necessarily leads to the formation of nano or ultrafine grains. To demonstrate this, two types of metallic materials (a slightly deformed 2024 aluminum alloy and nickel based single grain superalloys) have been irradiated 15 times by high current pulsed electron beam. Epitaxial growth was triggered during the re-solidification of the superalloys, leading to the formation of a deformed single grain. Thanks to the repeated combinations of epitaxial growth and solid state secondary recrystallization, the pulsed electron beam treatment has led to the formation of large (millimetric) grains, that were also 4 to 5 times thicker than the depth of the melted zone, at the surface of the aluminum alloy.