STEM observation of a multiphase nucleus of spheroidal graphite

Abstract

As part of a study on nucleation and growth of graphite in spheroidal graphite irons, sys-tematic transmission electron microscopy observations are carried out. For this, focused ionbeam is used to prepare thin foils that are precisely located and present an even thicknessthus allowing high quality characterization.In this work, a nucleus with an overall elongated shape that was found in a perfectly roundgraphite spheroid is investigated by scanning transmission electron microscopy (STEM) cou-pled with energy dispersive X-ray spectroscopy. The acquisition of STEM images at differenttilt of this nucleus is achieved which allows illustrating the precipitation process of the manyphases constituting it. For the first time, a remaining of inoculant could be identified withinthe nucleus. Furthermore, the elongated shape of the nucleus is a definitive proof that theshape of nucleus does not determine that of the emerging graphite precipitate