Novel TiB2-reinforced 316L stainless steel nanocomposites with excellent room- and high-temperature yield strength developed by additive manufacturing

Abstract Selective laser melting (SLM) is an emerging additive manufacturing process for fabricating multifunctional parts by locally melting and consolidating powders in a layer-by-layer manner. Its flexibility enables the development of new alloys and metal matrix composites with unique, fine microstructures and complex-shaped components that are all difficult to realize with traditional manufacturing processes. This study investigates how TiB 2 nanoparticle reinforcements affect the microstructure and high-temperature deformation behavior of a 316L stainless steel matrix. In SLM-processed pure stainless steel, fully directional columnar grains were observed, whereas TiB 2 nanoparticles added to the steel matrix significantly reduced the sizes of the molten pools and grains and disrupted the directional structures. A chemical analysis revealed no compositional difference between the boundary and interior of the molten pool areas of the SLM-processed TiB 2 /316L nanocomposites, suggesting that elements did not segregate macroscopically. However, for higher TiB 2 contents, alloying elements microsegregated at the boundaries of cellular structures due to the particle accumulation structure mechanism. Transmission electron microscopy confirmed the existence of mostly cube-like TiB 2 nanoparticles both at the boundaries and in the interiors of the cellular structures. The nanocomposites exhibited high compressive yield strength and ductility at room and high temperatures, except at 600 °C, where embrittlement was observed. Observing the microstructure and flow stress of nanocomposites deformed at 700 and 800 °C shed light on the dynamic recovery and dynamic recrystallization phenomena. However, several conventional strengthening mechanisms could not predict the entire yield strength increase. Thus, a novel microsegregation strengthening mechanism was presented to explain the effect of TiB 2 on the refined microstructure, and the novel microsegregation phenomenon and the enhanced mechanical properties were correlated. Hence, the SLM process shows high potential for fabricating new materials with outstanding properties.