Amidst the world of stainless steel manufacturing, a new panorama emerges. Slags, those byproducts of deoxidizers, have long been known to appear in traditional 316L stainless steel production. Ordinarily, these materials form a solid phase in the liquid metal, ready to be purged post-production.
However, the landscape shifts in the realm of laser powder bed fusion (LPBF) 3D printing. Researchers at LLNL unveil a unique discovery—slags, which are staples of standard manufacturing, linger on the surface in the LPBF process, instigating pitting corrosion.
“Pitting corrosion, enigmatic and capricious, has perplexed many. Yet, our team has unearthed the material attributes that spark this corrosion variant,” expressed Shohini Sen-Britain, the lead mind behind the revelatory Nature Communications exposé.
Behold, the art of 3D-printing steel.
In the labyrinth of scientific inquiry and experimentation at LLNL, researchers, equipped with an arsenal of high-tech tools, probed the enigma of the slags that orchestrate corrosion in simulated aquatic environments.
Illuminating the Role of Slags
With a fusion of cutting-edge methods like plasma-focused ion beam milling and X-ray photoelectron spectroscopy, the team delved into the intricate structure of AM stainless steel components.
Delving deep, they unraveled the nefarious role of slags in the corrosion process, as these entities birthed vulnerabilities, inviting chloride-laden waters to infiltrate the metal, sowing chaos within. Moreover, these slags harbor metal inclusions that dissolve upon confrontation with the brine-like milieu, further stoking the corrosion inferno.
Brandon Wood, the project’s esteemed principal investigator, articulated, “Under the lens, we sought the source of corrosion within these materials. Our quest was met with a peculiar sight—an alloyed secondary phase, rich in manganese: the harbinger of malevolence. By scrutinizing the surroundings of these slags, we unlocked a troubling truth.”
Employing transmission electron microscopy, the researchers plucked minuscule samples from the stainless steel’s surface, peering at the slags through the microscope, unraveling their atomic tapestries of chemistry and structure.
Vigilance Against Corrosion
The saga of corrosion unfolds before our eyes, a tale of convoluted interactions contributing to pitting corrosion. These revelations offer a novel perspective on the slags, a vista hitherto unexplored in the realm of AM.
Thomas Voisin, the vanguard investigator, reflected, “As the laser dances, melting the material in its wake, a rapid solidification follows. This abrupt shift traps the atoms in an unnatural dance, altering both the mechanical and corrosion properties of the metal.”
Voisin underscores the criticality of monitoring corrosion in stainless steel applications, especially in the maritime domain, where the metal finds ample utility.
This venture signposts a significant stride in the perpetual war against corrosion. It not only enriches our comprehension of this corrosive dance but also ushers in the dawn of improved materials and manufacturing pathways.
By unmasking the machinations behind pitting, Sen-Britain and Voisin plot a course towards fortifying the resilience and longevity of 3D-printed stainless steel. The next juncture beckons them to reformulate the powder feedstock, excising manganese and silicon to stymie—if not extinguish—slag emergence.
