Thermal cycling of Fe3Al based iron aluminide during the wire-arc additive manufacturing process: An in-situ neutron diffraction study

Fe3Al based iron aluminide has continuously been attractive because of its excellent oxidation resistance, corrosion resistance, light weight and low material cost. It has been considered as a promising replacement of regular stainless steel in fossil energy industry. However, the industrial application of iron aluminide is limited by its low room temperature ductility and high fabrication cost. In recent years, additive manufacturing processes have been proved capable of producing iron aluminide with relatively lower cost as compared to traditional powder metallurgy processing. In the present research, the influence of thermal cycling during the additive manufacturing of Fe3Al based iron aluminide on the phase fraction inside the deposited material has been simulated and investigated using in-situ neutron diffraction. Upon heating, the Fe3Al based iron aluminide has experienced Fe3Al <-> FeAl phase transformations, FeAl phase ordering-disordering, and Fe3Al phase transformation from imperfectly ordered B2 structured to perfectly ordered DO3 structure. Also, the existence of the forbidden Fe3Al 110 reflection has been determined by neutron diffraction and further evaluated. In addition, the variation of phase fractions throughout the heat treatment has been quantitatively analyzed by Rietveld refinement.