STEM observation of a multiphase nucleus of spheroidal graphite

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