A hybrid directed energy deposition process to manipulate microstructure and properties of austenitic stainless steel

Owing to the relatively lower dimensional accuracy and poorer surface finish compared to other additive manufacturing (AM) technologies, directed energy deposition (DED) yields parts that often require extensive post-processing. Thus, it is well suited to be combined with subtractive or deformation processes into hybrid manufacturing strategies, which may enable microstructure engineering of near-net-shape parts directly upon production. In this work, we use a custom-made machine that combines DED and single point incremental forming (SPIF) processes to produce samples of stainless steel 316L which are amenable to undergo recrystallization upon heat treatment. After recrystallization, the microstructure exhibits a high density of twin boundaries, which are known to enhance the physical and mechanical properties of alloys. We investigate how different SPIF parameters affect the extent of recrystallization and find that our strategy may be used to produce both gradient and “sandwich” microstructures, which integrate dissimilar grain boundary character distributions and grain structures. We assess the corrosion resistance and mechanical properties of such samples and discuss the resulting performance enhancement. Our results showcase new opportunities for microstructure engineering of DED components and lay the groundwork for the design of AM processes that enable grain boundary engineering of metal alloys.National Research Foundation (NRF)Published versionThis work was supported by the National Research Foundation (NRF) Singapore, under the NRF Fellowship programme (NRF-NRFF2018-05)