Abstract

The objective of this study is to investigate the thermal stability of dislocation structure and its effect on the creep behaviour of laser-directed energy deposited 316L stainless steel (L-DED-316L SS). Post-processing heat treatments at temperatures ranging from 300 to 1200 °C were performed on the as-deposited DED samples. The microstructural changes induced by the heat treatment were correlated to the corresponding variations of the room temperature tensile properties and creep behaviour at 650 °C/225 MPa. Results show that dislocations produced during DED process tend to distribute uniformly, with only a few localized fine dislocation cells (average cell size of ∼0.4 μm) being detected. At 600 °C, the remaining dislocations rearrange and organize into a coarse dislocation cell structure with an average cell size of ∼1.6 μm, leading to a slight decrease in yield strength, while the creep performance is not obviously affected. At 800 °C, the annihilation of dislocations and destruction of dislocation cell structure, as well as elemental diffusion contribute to a significant drop in yield strength and creep rupture time with a noticeable increase in steady creep rate. Further increasing heat treatment temperature above 1000 °C removes the dislocation cell structure and elemental segregation on cell walls, which results in a continuous increase in steady creep rate. The present work demonstrates that the presence of chemical micro-segregation is crucial for the stabilization of dislocation cells structure and the resulted creep performance of the heat-treated L-DED samples.

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