A team of scientists has 3D printed a dual-phase nanostructured, high-entropy alloy that exceeds the strength and ductility of other state-of-the-art additive manufacturing materials. This breakthrough could lead to higher performance parts for aerospace, medical, energy and transportation applications. The work was done by researchers at the University of Massachusetts Amherst and the Georgia Institute of Technology. It was led by Wen Chen, associate professor of mechanical and industrial engineering at the University of Massachusetts Amherst, and Ting Zhu, professor of mechanical engineering at Georgia Tech, and was published Aug. 3 in the journal Nature.
Over the past 15 years, high entropy alloys (HEAs) have become increasingly popular as a new paradigm in materials science. They consist of five or more elements in nearly equal proportions, providing alloy design with the ability to create a nearly infinite number of unique combinations. Traditional alloys, such as brass, stainless steel, carbon steel and bronze, contain a combination of one major element with one or more trace elements.
3D printing, also known as additive manufacturing, 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 unattainable with traditional routes. However, “the potential to leverage the combined benefits of additive manufacturing and HEA to achieve new properties remains largely unexplored,” said Ting Zhu.
Wen Chen and his team in the UMass Multiscale Materials and Manufacturing Laboratory have combined HEA with the most advanced 3D printing technology, laser powder bed melting, to develop new materials with unprecedented properties. Because the process causes the material to melt and solidify very rapidly compared to traditional metallurgical processes, “you get a very different microstructure that is far from equilibrium,” Chen said. This microstructure looks like a web of alternating layers of nano-stellar structures called face-centered cubic lattices (FCC) and body-centered cubic lattices (BCC), embedded in microscopic eutectic clusters with random orientations. The hierarchical nanostructured HEA makes cooperative deformation of the two phases possible.
This unusual microstructural rearrangement of atoms produced ultra-high strength as well as enhanced ductility, which is uncommon because normally strong materials tend to be brittle,” said Chen. Compared to conventional metal casting, we get almost three times the strength, and not only do we not lose ductility, but we actually increase ductility at the same time. For many applications, the combination of strength and ductility is key. Our findings are original and exciting for both materials science and engineering.”
“The ability to produce high-strength and ductile HEAs means that these 3D printed materials are stronger in resisting deformation in applications, which is important for lightweight structural designs that improve mechanical efficiency and energy efficiency,” said Jie Ren, first author of the paper.
Ting Zhu’s group at the Georgia Institute of Technology led the computational modeling for this study. They developed a computational model of biphasic crystal plasticity to understand the mechanical roles played by FCC and BCC nanoparticles and how they work together to increase the strength and ductility of the material.
“Our simulations show a surprising strength and hardening response of the BCC nanoparticles, which is critical to achieve the excellent strength and ductility synergy of our alloy.” Said Ting Zhu, “This mechanistic understanding provides an important foundation to guide the future development of 3D printed HEAs with exceptional mechanical properties.”
In addition, 3D printing provides a powerful tool to manufacture geometrically complex and customized parts. In the future, leveraging 3D printing technology and the vast alloy design space of HEAs offers substantial opportunities for the direct production of end-use parts for biomedical and aerospace applications.