Controlling the Thermal Stability of Additively Manufactured Alloys—A New Materials Design Paradigm

The rapid solidification conditions and repeated thermal cycles typical of fusion-based additive manufacturing (AM) processes yield metal alloys with complex, non-equilibrium microstructures. By controlling the evolution of such microstructures—either during AM or through post-processing—it is possible to create new materials with tailored properties and improved performance. In this work, we demonstrate this capability by controlling the thermal stability of 316L steel and nickel-base alloy 725 produced via laser powder bed fusion (LPBF). We show that the propensity of the alloys to recrystallize mainly depends on the solidification microstructure—including the cell size and the amount of solute that decorates their interfaces—which may be tuned by changing the LPBF parameters. By alternating different laser scanning strategies throughout the build, we demonstrate the capability of activating recrystallisation site-specifically in both alloys. Using this approach, we produce a variety of “microstructure architectures” consisting of regions with markedly different grain boundary character distribution and mechanical behavior. We test these new materials to assess their bulk mechanical properties and resistance to intergranular degradation. Our results showcase the additional opportunity offered by AM to design novel materials with complex microstructures.