Exploiting additive manufacturing-induced cellular structures for the design of precipitation-strengthened alloys

One of the key characteristics of additively manufactured (AM) alloys is the emergence of cellular structures, in which cell boundaries predominantly manifest as a combination of solute segregation and dislocation walls. Consequently, cell structures encompass regions exhibiting compositional and structural gradients when moving from cell cores to cell boundaries. This provides a distinctive window into the local variations in phase stability, which significantly influences the material’s phase transformation behavior and can be actively leveraged during post-AM heat treatments to facilitate the site-specific formation of precipitates at cell boundaries. Inspired by these insights, we computationally designed an Al10.5Co25Fe39.5Ni25 multi-principal element alloy to utilize this phenomenon. The alloy’s composition was chosen to segregate Al, a fast-diffusing, precipitate-forming element, into the interdendritic regions during the AM process and aligned solute segregation with dislocation walls at the cell boundaries. This created a “pre-conditioned” state with an enhanced local chemical driving force and a reduced nucleation barrier for precipitate formation before aging. Comprehensive multi-scale characterization, including in situ synchrotron X-ray diffraction (SYXRD), was performed to evaluate the influence of cellular structures on precipitation kinetics, precipitate size and volume fraction, and the evolution of mechanical properties after aging treatment relative to a reference condition in which cellular structures were removed via solution annealing before aging. The results are critically discussed to reveal the interplay between cellular structures and phase transformation behavior, offering key insights into engineering the microstructures of AM alloys via post-AM heat treatments.