Researchers from the University of Massachusetts Amherst and the Georgia Institute of Technology have 3D printed a two-phase nanostructured high-entropy alloy that exceeds the strength and ductility of other modern additively manufactured materials, potentially leading to higher -For performance components used in aerospace, medicine, energy and transportation. The work, led by Wen Chen, assistant professor of mechanical and industrial engineering at UMass, and Ting Zhu, professor of mechanical engineering at Georgia Tech, was published online in the journal Nature.
In the last 15 years, high entropy composites (HEAs) have become very popular as a new material science. Consisting of five or more elements in nearly equal proportions, they provide the ability to create a wide variety of unique combinations for alloy design. Traditional alloys such as brass, carbon steel, stainless steel, and bronze contain a primary element combined with one or more trace elements.
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Additive manufacturing, also known as 3D printing, has recently emerged as a powerful approach to material development. Laser-based 3D printing can produce large temperatures and high cooling rates that are not easily achievable by conventional means. However, “the potential to exploit the combined benefits of additive manufacturing and HEAs to discover new properties has yet to be explored,” Zhou says.
Chen and his team at the Multimaterials and Manufacturing Laboratory combined HEA with the latest 3D printing technique to develop new materials, laser powder bed composite (called laser powder bed composite), which has been created in an unprecedented manner. Because the process allows materials to melt and solidify faster than traditional metalworking, “you get a very different microstructure that’s out of scale,” says Chen. This microstructure resembles a network and is made up of alternating layers called face-centered cubic (FCC) and body-centered cubic (BCC) nanolamellar structures. Hierarchical nanostructured HEA enables cooperative degradation of the two phases.
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“This unusual micro-atomic arrangement results in extremely high strength and an improved tube, which is unusual because usually solid materials are brittle,” Chen says. Compared to conventional cast iron, he says, “We’ve almost tripled our strength, and not only have we not lost flexibility, but we’ve increased it at the same time.” “The combination of strength and ductility is key for many applications. Our findings are original and exciting for materials science and engineering alike.”
“The ability to produce strong and ductile HEAs means that these 3D printed materials are more robust in resisting applied deformations, resulting in a lightweight structural design for improved mechanical efficiency and energy efficiency,” says Ji Ren, Chen’s Ph.D. student and first author of the paper.
Zhu’s team at Georgia Tech led the computational modeling for the research. He developed computational models of two-phase crystal plasticity to understand the mechanical roles played by both FCC and BCC nanolamellas and how they work together to give the material increased strength and stiffness.
“Our simulation results show the remarkable high-strength but high-toughness responses of BCC nanolamellae, which are key to achieving superior strength-ductility composites. This mechanical understanding provides an important basis for tailoring 3D printed HEAs with unique mechanical properties, Zhu says.
In addition, 3D printing provides a powerful tool for making geometrically complex and custom parts. In the future, the use of 3D printing technology and the wide alloy design space of HEAs will open up vast possibilities for the direct production of end-use components for biomedical and aerospace applications.
Additional research partners on the paper include Texas A&M University, University of California Los Angeles, Rice University, and Oak Ridge and Lawrence Livermore National Laboratories.
The paper is available here: https://www.nature.com/articles/s41586-022-04914-8
