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

Abstract

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 TiB2 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 TiB2 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 TiB2/316L nanocomposites, suggesting that elements did not segregate macroscopically. However, for higher TiB2 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 TiB2 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 TiB2 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.