Enhanced thermal stability of the cellular structure through nano-scale oxide precipitation in 3D printed 316L stainless steel

Abstract

• The thermal stability of the cellular structure in the 316L stainless steel could be improve by the nano-scale oxide precipitation. • Oxides at different heat treatment temperature were identified. • The relationship between the evolution of cellular structure and the oxide precipitates was investigated. The cellular structure is one of the reasons for the improvement of 316 L performance which fabricated by additive manufacturing technology. However, the cellular structure tends to disappear at high temperatures. In this study, oxide nanoparticles were introduced into the 316 L matrix to improve the thermal stability of the cellular structure, this material was successfully fabricated by mechanical alloying followed with laser-powder-bed-fusion (LPBF). The thermal stability of the cellular structure in 316 L was tested with isothermal heat treatment at 1073 K, 1173 K and 1273 K, respectively. The microstructural stability of the cellular was characterized with scanning electron microscopy, transmission electron microscopy (TEM), electron backscatter diffraction, X-ray diffraction measurements and Vickers microhardness testing. The cellular structure was stable at 1073 K due to the dispersed precipitates pining the dislocations at its boundary. The chemical composition of the oxide precipitates with sizes in the range of 10–200 nm was examined by TEM combined with an energy dispersive spectrometry. This work provided a method to enhance the thermal stability of the microstructure of the additively manufactured stainless steel 316 L.