Abstract
Laser powder bed fusion (LPBF) has been increasingly used in the fabrication of dense metallic structures. However, the corrosion related properties of LPBF alloys, in particular environment-assisted cracking, such as corrosion fatigue properties, are not well understood. In this study, the corrosion and corrosion fatigue characteristics of LPBF 316L stainless steels (SS) in 3.5 wt.% NaCl solution have been investigated using an electrochemical method, high cycle fatigue, and fatigue crack propagation testing. The LPBF 316L SSs demonstrated significantly improved corrosion properties compared to conventionally manufactured 316L, as reflected by the increased pitting and repassivation potentials, as well as retarded crack initiation. However, the printing parameters did not strongly affect the pitting potentials. LPBF samples also demonstrated enhanced capabilities of repassivation during the fatigue crack propagation. The unique microstructural features introduced during the printing process are discussed. The improved corrosion and corrosion fatigue properties are attributed to the presence of columnar/cellular subgrains formed by dislocation networks that serve as high diffusion paths to transport anti-corrosion elements.
Highlights
Powder-based additive manufacturing (AM) techniques, such as laser powder bed fusion (LPBF) [1], are mostly used in the fabrication of dense metallic structures
In LPBF alloys, nanoscale oxide inclusions (100 to 200 nm in diameter) enriched with Si, Al, and Mn were observed along the dislocation cell boundaries [11] instead of the MnS inclusions found in conventional ones
We have studied LPBF 316L SSs because it is of particular interest in marine, nuclear and biomedical applications. 316L possesses relatively superior ductility and excellent corrosion resistant properties over other materials
Summary
Powder-based additive manufacturing (AM) techniques, such as laser powder bed fusion (LPBF) [1], are mostly used in the fabrication of dense metallic structures. The rapid solidification process and complex thermal cycles in AM can lead to unique microstructural features, defects, and residual stress that can result in properties drastically different from that of conventionally manufactured parts [2]. The microstructure and mechanical properties of alloys made from AM techniques have been studied extensively, there is a lack of deeper understanding regarding their corrosion related properties. Nonequilibrium/atypical phase: Conventionally manufactured SSs contain MnS inclusions that typically reduce corrosion resistance. In LPBF alloys, nanoscale oxide inclusions (100 to 200 nm in diameter) enriched with Si, Al, and Mn were observed along the dislocation cell boundaries [11] instead of the MnS inclusions found in conventional ones. The LPBF alloys are reported to have enhanced pitting resistance due to the absence of MnS [5] in sodium chloride solution. In high temperature water, these oxide inclusions are reported to promote early initiation of microvoids and cause crack branching [12]
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