Researchers at UMass Amherst and Georgia Tech have 3D printed a dual-phase nanostructured high-entropy alloy that exceeds the strength and ductility of other advanced additively manufactured materials.
Wen Chen, assistant professor of mechanical and industrial engineering at UMass Amherst, stands in front of images of 3D-printed high-entropy alloy components (radiator fan and octect array, left) and a reverse pole figure map cross-sectional electron backscatter diffraction showing a microstructure of randomly oriented nanolamellae (right).
A team of researchers from the University of Massachusetts Amherst and the Georgia Institute of Technology have 3D printed a dual-phase nanostructured high-entropy alloy that exceeds the strength and ductility of other additively fabricated materials at the cutting edge of technology, which could lead to higher performance components for applications in aerospace, medicine, energy and transportation. The research, 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 in the August issue of the journal Nature.
Over the past 15 years, high entropy alloys (HEAs) have become increasingly popular as a new paradigm in materials science. Composed of five or more elements in nearly equal proportions, they offer the possibility of creating an almost infinite number of unique combinations for alloy design. Traditional alloys, such as brass, carbon steel, stainless steel and bronze, contain a primary element associated with one or more trace elements.
Additive manufacturing, also known as 3D printing, has recently emerged as a powerful approach to materials development. Laser-based 3D printing can produce large temperature gradients and high cooling rates that are not easily accessible through conventional routes. However, “the potential to exploit the combined advantages of additive manufacturing and HEAs to achieve new properties remains largely unexplored,” says Zhu.
Chen and his team at the Multi-Scale Materials and Fabrication Lab combined an HEA with a cutting-edge 3D printing technique called laser powder bed fusion to develop new materials with unprecedented properties. Because the process melts and solidifies materials very quickly compared to traditional metallurgy, “you get a very different microstructure that’s far from equilibrium” on the components created, Chen says. This microstructure is net-like and consists of alternating layers known as face-centered cubic (FCC) and body-centered cubic (BCC) nanolamellar structures embedded in microscale eutectic colonies with random orientations. . The hierarchical nanostructured HEA allows the cooperative deformation of the two phases.
“The atomic rearrangement of this unusual microstructure gives rise to ultra-high strength as well as improved ductility, which is rare because generally solid materials tend to be brittle,” Chen says. Compared to conventional metal casting, “we almost tripled the strength and not only did we not lose ductility, but we actually increased it simultaneously,” he says. “For many applications, a combination of strength and ductility is essential. Our discoveries are original and exciting for materials science and engineering.
“The ability to produce strong and ductile HEAs means that these 3D printed materials are stronger to resist applied deformation, which is important for lightweight structural design for improved mechanical efficiency and energy savings,” says Jie Ren, Ph.D. of Chen. student and first author of the article.
Zhu’s group at Georgia Tech led computer modeling for the research. He developed computational models of two-phase crystal plasticity to understand the mechanistic roles played by FCC and BCC nanolamellae and how they work together to give the material additional strength and ductility.
“Our simulation results show the surprisingly high strength and hardening responses of BCC nanolamellae, which are key to achieving the exceptional strength-ductility synergy of our alloy. This mechanistic understanding provides an important foundation to guide the future development of 3D-printed HEAs with exceptional mechanical properties,” Zhu said.
Additionally, 3D printing offers a powerful tool for making geometrically complex and custom parts. In the future, the exploitation of 3D printing technology and the vast alloy design space of HEAs will open many opportunities for the direct production of end-use components for biomedical and aerospace applications.
Other 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.
Story by Melinda Rose, associate news editor at UMass Amherst.