From -196°C to 600°C... 3D Printing Produces High-Strength Alloy [Reading Science]

POSTECH team achieves strength and ductility without post-heat treatment
Harnessing nanoscale structures inside the alloy... Potential for cryogenic storage and aerospace materials

A metal alloy that maintains high strength and ductility from cryogenic temperatures as low as -196°C to high temperatures of 600°C has been developed. By harnessing the microstructure formed inside the metal during 3D printing, the researchers created a material that is both strong and highly stretchable without requiring separate post-heat treatment. The alloy is expected to be used in structural metal components for cryogenic storage facilities and the aerospace sector.

The National Research Foundation of Korea announced on November 5 that a research team led by Professor Kim Hyungseop of POSTECH’s Graduate School of Eco-Friendly Materials had developed an alloy that maintains its strength and ductility over a wide temperature range by harnessing the precipitate network structure and interface properties formed during 3D printing.

Alloy deformation behavior depending on precipitate-network structure and interfaces. BCC precipitates form a network within the alloy’s FCC matrix. During deformation, some interfaces induce plastic deformation within the precipitates, enhancing ductility, while others cause dislocations to accumulate, increasing strength. Provided by Park Hyojin, postdoctoral researcher at Pohang University of Science and Technology (POSTECH).

The findings were published online on November 2 in Nature Materials, an international journal in the field of materials science.

Metal materials generally tend to lose ductility—the ability to stretch—when their strength is increased. This is especially true at cryogenic or high temperatures, where changes in the way metals deform make it even more difficult to achieve both strength and ductility at the same time. Previously, strength was increased by forming fine precipitates inside the metal, but parts made by 3D printing often required separate heat treatment to achieve the desired microstructure.

To overcome these limitations, the research team focused on how metal melts and solidifies rapidly during 3D printing. They designed the process so that precipitates would form a network-like structure inside the alloy as metal powder was melted by a laser and built up layer by layer.

Precipitates are microscopic regions inside an alloy that have a different composition or crystal structure from the surrounding metal. The research team confirmed that the boundaries between the precipitates and the surrounding base metal, known as the matrix—in other words, the interfaces—play an important role in increasing both the metal’s strength and ductility.

Tensile tests on the alloy showed that it achieved a yield strength of more than 1 gigapascal (GPa) and a uniform elongation of 19-26% at all three test temperatures: -196°C, room temperature (25°C), and 600°C. Yield strength is the stress at which permanent deformation begins in a metal, while uniform elongation is the percentage by which a material stretches evenly before deformation becomes concentrated in a specific area.

Electron microscopy analysis showed that the interfaces between the precipitates and the matrix perform different roles. Some interfaces impede deformation inside the metal, increasing its strength, while others transfer deformation to the precipitates, allowing them to stretch along with the surrounding metal. These two effects occur simultaneously, helping the material remain strong without breaking easily.

Kim Hyungseop, professor at POSTECH's Graduate School of Eco-Friendly Materials (left, corresponding author); Renhao Wu, a postdoctoral researcher at Tohoku University in Japan (corresponding author); and Park Hyojin, a postdoctoral researcher in POSTECH's Department of Materials Science and Engineering (first author). Photo provided by POSTECH.

The research team also used calculations at the atomic scale to confirm that these deformation mechanisms are not significantly affected by temperature changes. The alloy also exhibited work hardening, in which resistance to deformation increases as the alloy stretches, allowing it to achieve high elongation.

This study is significant because it achieved excellent mechanical properties over a wide temperature range using only the 3D printing process, without separate post-heat treatment. However, further verification is needed to determine whether the same performance can be achieved in large components and whether the properties will be maintained under repeated loading and prolonged exposure to high temperatures before the alloy can be used in industry.

“This study is significant in that it presents a new alloy design and strengthening strategy based on the precipitate network structure and interface properties formed during 3D printing,” Professor Kim said. “Further verification of manufacturing reproducibility and long-term durability is needed to enable the material’s practical use in metal components for cryogenic storage facilities and the aerospace sector.”

This content was produced with the assistance of AI translation services.