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A D V A N C E D M A T E R I A L S & P R O C E S S E S | J A N U A R Y / F E B R U A R Y 2 0 2 2 4 8 3D PRINTSHOP An investigation of printed stainless steel revealing a heterogeneous–and correlative–distribution of crystal defects in the bright-field transmission electron micrograph (grayscale) and alloying elements in the superimposed x-ray fluorescence map (colored). Courtesy of W. Streit Cunningham and Prof. Jason Trelewicz, Stony Brook University. SYNCHROTRON TECHNIQUES HELP 3D PRINT BETTER STEEL Researchers are using synchrotron x-ray techniques to study connections between corrosion behavior and mate- rials structure in laser additively manu- factured 316L stainless steel. The study, led by Stony Brook University, uncov- ered new connections between printing parameters and the defect state in the material. This enables the researchers to map pathways for engineering an even better corrosion-resistant printed alloy. The findings, published in Additive Manufacturing, could enable the future production of a highly corrosion resis- tant stainless steel by engineering its defects at the nanoscale. The research also demonstrated that multimodal synchrotron techniques are becoming essential tools in establishing correla- tions between the printing process, un- derlying structure of the material, and its realized performance. “The major focus of our study was to understand the corrosion behavior of laser additively manufactured 316L stainless steel in the con- text of microstructural defects that form due to the rapid solidification rates inherent to this 3D printing process,” ex- plains Jason Trelewicz, corresponding author and associate professor. “We show that while uniform surface corrosion of the printed 316L is similar to a traditional 316L alloy, the printed material ex- hibits an increased sus- ceptibility to pitting, par- ticularly in the samples with the greatest defect density uncovered from synchrotron measure- ments.” stonybrook.edu. 3D-PRINTED SAND HAS SUPER STRENGTH A team from the Department of Energy’s Oak Ridge National Labora- tory (ORNL) has tailored a polyeth- yleneimine (PEI) binder that doubles the strength of sand parts compared with conventional binders. The novel polymer is used to bind and strengthen silica sand for binder jet additive manu- facturing, a method used by industries for prototyping and part production. The printable polymer enables sand structures with intricate geometries and exceptional strength—and is also water soluble. Parts printed via binder jetting are initially porous when removed from the print bed. They can be strengthened by infiltrating the design with an addition- al super-glue material called cyanoac- rylate that fills in the gaps. This second step provided an eight-fold strength in- crease on top of the first step, making a polymer sand composite stronger than any other and any known building ma- terials, including masonry. “Few polymers are suited to serve as a binder for this application. We were looking for specific properties, such as solubility, that would give us the best result. Our key finding was in the unique molecular structure of our PEI binder that makes it reactive with cyanoacrylate to achieve exceptional strength,” says ORNL’s Tomonori Saito, a lead researcher on the project. One potential application for the super-strength sand is to advance tooling for composites manufacturing. Lightweight materials such as carbon fiber or fiberglass are wrapped around 3D-printed sand cores, or “tools,” and cured with heat. Silica sand is attractive for tooling because it does not change dimensions when heated and because it offers a unique advantage in wash- able tooling. In composite applications, using a water-soluble binder to form sand tools is significant because it en- ables a simple washout step with tap water to remove the sand, leaving a hol- low composite form. Current sand-casting molds and cores have limited industrial use be- cause commercial methods such as washout tooling apply heat and pres- sure that can cause sand parts to break or fail on the first try. Stronger sand parts are needed to support manufac- turing at a large scale and enable rapid part productio n. ornl.gov. A 6.5-cm 3D-printed sand bridge held 300 times its own weight. Courtesy of Dustin Gilmer/University of Tennessee, Knoxville.