Abstract
316L stainless steel (316L SS) is a flagship material for structural applications in corrosive environments, having been extensively studied for decades for its favorable balance between mechanical and corrosion properties. More recently, 316L SS has also proven to have excellent printability when parts are produced with additive manufacturing techniques, notably laser powder bed fusion (LPBF). Because of the harsh thermo-mechanical cycles experienced during rapid solidification and cooling, LPBF processing tends to generate unique microstructures. Strong heterogeneities can be found inside grains, including trapped elements, nano-inclusions, and a high density of dislocations that form the so-called cellular structure. Interestingly, LPBF 316L SS not only exhibits better mechanical properties than its conventionally processed counterpart, but it also usually offers much higher resistance to pitting in chloride solutions. Unfortunately, the complexity of the LPBF microstructures, in addition to process-induced defects, such as porosity and surface roughness, have slowed progress toward linking specific microstructural features to corrosion susceptibility and complicated the development of calibrated simulations of pitting phenomena. The first part of this article is dedicated to an in-depth review of the microstructures found in LPBF 316L SS and their potential effects on the corrosion properties, with an emphasis on pitting resistance. The second part offers a perspective of some relevant modeling techniques available to simulate the corrosion of LPBF 316L SS, including current challenges that should be overcome.
Highlights
As on-demand, highly customizable products become increasingly commonplace, specialized industries, including aerospace, naval, energy, and defense, are seeking alternatives to well-established manufacturing processes that offer higher versatility
In situ techniques such as high-speed atomic force microscopy (AFM) or transmission electron microscope (TEM) are critical to this effort; their benefit is magnified when combined with advanced simulation methods, which are often better equipped to unravel the individual and collective effects of microstructural features at different length scales
We review the progress in simulating pit nucleation and propagation in stainless steel (SS) using finite element modeling (FEM), phase-field modeling (PF) and the cellular automaton (CA) approach
Summary
As on-demand, highly customizable products become increasingly commonplace, specialized industries, including aerospace, naval, energy, and defense, are seeking alternatives to well-established manufacturing processes that offer higher versatility. Measurements and calculations of residual stresses in LPBF materials have been carried out in the bulk or the near-surface region rather than at the surface, where the stress state may differ due to the relaxed constraints or be directly affected by the melt pool dynamic Another indirect effect of residual stress on the corrosion properties is the formation of the high density of dislocations, which can affect the nature of the passive oxide film. For better understanding of the corrosion mechanisms and certification of the LPBF parts in corrosive environments, quantitative characterization of key local phenomena occurring during passive film breakdown and metastable pitting are necessary In situ techniques such as high-speed AFM or TEM are critical to this effort; their benefit is magnified when combined with advanced simulation methods, which are often better equipped to unravel the individual and collective effects of microstructural features at different length scales. This refined database was coupled to regression-based ANN to uncover hidden relationships between the chloride threshold and the relevant primary variables (temperature, pH, corrosion potential, and breakdown potential), which are in turn determined by secondary variables (cement composition, porosity, and water/cement ratio)
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