Just as a snowflake's intricate structure vanishes when it melts and transforms when it refreezes, the microstructure of metals can change during the 3D printing process, resulting in strengths or weaknesses in the printed product.
Cornell researchers have uncovered a way to control these transformations in metal solidification by adjusting alloy composition, ultimately leading to stronger, more reliable metal parts. The findings, published Feb. 12 in Nature Communications, offer an unprecedented view inside the phase changes that occur during the 3D printing process and could improve materials used for additive manufacturing.
"A major problem is that most of the materials we print form column-like structures that can weaken the material in certain directions," said senior author Atieh Moridi, assistant professor and an Aref and Manon Lahham Faculty Fellow in the Sibley School of Mechanical and Aerospace Engineering, in Cornell Engineering. "We discovered that by adjusting the composition of the alloys, we can essentially disrupt these column-like structures and make a more uniform material."
By adjusting the relative amounts of manganese and iron in their starting material, the team disrupted columnar grain growth, significantly reduced grain size and improved the yield strength of the finished metal.
"Microstructural features, like grain size, are the building blocks that govern material performance and properties" Moridi said. "The material composition controls the phase stability, which was the key for us to control the microstructure."
The column-like grain structures form and grow in just a fraction of a second during the phase change in the printing process, which is why scientists had previously struggled to study this phenomenon, said the study's first author, Akane Wakai, Ph.D. '24.
"The difficult part was trying to resolve these very short spans of time where the material goes from liquid state to solid state," Wakai said. The final product has no fingerprint of its earlier state, so it is like trying to figure out what a snowflake looked like from a drop of melted water.
The team overcame this roadblock by utilizing the Cornell High Energy Synchrotron Source to obtain fraction-of-a-second data about their materials during the printing process. In the best-performing sample, Moridi said, "we found evidence of an intermediate phase that can help disrupt those column-like grains and refine the grain structure."
Understanding the material properties of the starting alloy and resulting phase changes could represent a new foundation for choosing metal for 3D printing.
"The findings from this research can be used for real-life applications to create more reliable materials that enable even better performance," Wakai said. "Not too far into the future, we'll start seeing 3D printed metal parts, even in consumer products like cars or electronics."
Increasing the reliability of 3D metals could be a boon for the manufacturing field. Wakai noted that 3D printing of metal has a "freedom of design that can lead to weight reduction, shortened manufacturing time, minimized material waste, and can create features that are otherwise really difficult or impossible to fabricate through conventional methods."
Collaborators included researchers from the NASA and the University of Pittsburgh. Funding for their work came from the U.S. Department of Energy, National Science Foundation and NASA.
Melia Matthews is a freelance writer for Cornell Engineering.
