Direct energy deposition of high strength austenitic stainless steel matrix nanocomposite with superior ductility: Microstructure, tensile properties, and deformation behavior

Direct energy deposition (DED) was used to additively manufacture 22-13-5 austenitic stainless steel (SS), of which the mechanical properties and corrosion resistance are superior to those of SS316L and SS304L. Additionally, in-situ formed oxide-driven strengthening was utilized in this study. The DED-processed austenitic SS matrix nanocomposite (SSMNC) exhibited unique microstructural features of heterogeneous grains and dislocation networks. The nano-sized precipitates existed at the sub-structure boundaries and decorated the dislocation network. The results of the transmission electron microscopy (TEM)-energy loss spectroscopy (EELS) analyses revealed nano-sized precipitates with an average size of 21.1 nm that were identified as (Mn,Cr)-rich oxides. This means that, during the DED process, the oxygen in the powder feedstock transformed into nano-sized oxide particles by rapid solidification. The DED-processed SSMNC revealed a yield strength of 705.4 +/- 5.3 MPa, which is higher than those of reported AM-processed stainless steels. In addition, the elongation-to-failure was measured as 41.8 +/- 3.5%. This suggests that the DED-processed SSMNC has an excellent combination of strength and ductility at room temperature. The high ductility of the alloy developed in this work was found to be achieved by a twinning-induced plasticity (TWIP) mechanism that operated during the deformation. Based on the above findings, the relationships between the microstructure, mechanical properties, and deformation mechanism are also discussed.