| Abstract Scope |
Welding and additive manufacturing processes produce a range of solidification conditions in nickel base alloys that are primarily characterized by significant elemental segregation within interdendritic and intercellular regions. Within these segregated regions, a range of secondary phases can form, depending on the compositions of the starting alloy systems. In Inconel 625, the allowable ranges of alloying element compositions can be rather wide, with Fe levels allowed to vary by 5 % mass fraction. A rather wide range of mechanical properties and microstructures can result, with different precipitate types and morphologies, which contribute to these different properties, originating from a complex interplay between iron, silicon, and titanium. Much of the focus on secondary phases has been on the formation of Laves phase, which has traditionally been attributed to the presence of higher iron levels and silicon contents in excess of 0.05 % mass fraction are also required to promote its formation. However, nitrogen levels on the order of 0.1 % mass fraction have been shown to drive the precipitation of a range of unanticipated nitride phases, with small changes in chemistry driving the formation of cubic metal nitrides (MN), tetragonal Z-phase (CrNbN), and diamond-cubic metal η-nitrides (M6N) in an Inconel 625 alloy with relatively low Fe (1 %), low Ti (0.02 %), and high Si (0.39 %) mass fractions. Conversely, these phases were replaced by only MN nitrides in a similar Inconel 625 alloy with elevated mass fractions of Ti (0.21 %) and Fe (4 %). The presence of these Nb-rich precipitates have demonstrated beneficial effects by consuming excess niobium in the interdendritic regions, thus limiting δ-phase formation and leading to the possibility of improved high temperature properties for additively manufactured components. |