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.

Automated summary

Direct energy deposition (DED) was used to additively manufacture 22-13-5 austenitic stainless steel (SS), which exhibited excellent mechanical properties and corrosion resistance. In-situ formed oxide-driven strengthening was utilized in this study. The DED-processed austenitic SS matrix nanocomposite (SSMNC) showed unique microstructural features and nano-sized precipitates, leading to high yield strength and ductility.