نبذة مختصرة : Due to the high cooling rate, laser powder bed fusion of 2205 duplex stainless steels results in non-equilibrium microstructures with >98 % δ-ferrite. A closer-to-equilibrium austenite fraction can be obtained through a solid-state phase transformation during a short heat treatment. However, an understanding of how the microstructures of the solidified δ-ferrite control this phase transformation is currently missing. Here, we discuss the δ-ferrite to austenite phase transformation in two distinct as-solidified microstructures using three-dimensional electron back-scatter diffraction, uncovering complex morphologies and interface crystallography that control the properties. Four types of austenite (intergranular, instability-induced, sympathetic, and intragranular) are formed and their interphase habit plane and curvature distributions after the heat treatment are studied. We show that the transformed microstructure will be different if crystallographic texture, dislocations, and precipitates in the δ-ferrite are altered by tuning the printing parameters. According to the grain boundary plane and curvature distributions, changes in δ-ferrite microstructure shifts the driving force for the intergranular transformation path from interfacial energy minimization towards strain energy minimization. The material printed with a reduced laser power and scan speed has lower dislocation density in the as-solidified state, which promotes a higher fraction of Kurdjumov-Sachs and Nishiyama-Wassermann δ-ferrite/austenite interfaces. This microstructure exhibits a weaker δ-ferrite texture, which limits the planar growth of austenite allotriomorphs and redirects thermal energy towards developing protrusions. These findings highlight the capability of additive manufacturing as a tool for microstructure engineering, via influencing the phase transformation product and the interfaces formed.
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