The high entropy alloys (in English High entropy alloys = HEA) are alloys formed by mixing equal or relatively large proportions of (usually) five or more elements. These multi-component alloys have attracted considerable interest over the past decade due to their intriguing structural, chemical and physical properties, but also due to their ability to create a near-infinite number of unique combinations for alloy design. .
This type of material is not yet regularly used in additive manufacturing, but recent advances reveal that selective laser melting, laser melting deposition, electron beam melting and arc additive manufacturing electric could process these materials.
As part of a research led by Wen Chenassistant professor of mechanical and industrial engineering at UMass, and Ting Zhu, professor of mechanical engineering at Georgia Tech, a team of scientists discovered that combining an HEA with laser powder bed fusion could create new materials with unprecedented properties.
As the process melts and solidifies materials very quickly compared to traditional metallurgy, “ we get a very different microstructure, far from equilibrium” on the components created, explains Chen. This microstructure resembles a net and is made up of alternating layers called face-centered cubic nanolamellar structures (in English face-centered cubic = FCC) and centered body cubic (in English body-centered cubic = BCC), embedded in micro-scale eutectic colonies with random orientations. The hierarchical nanostructured HEA allows cooperative deformation of the two phases.
” The atomic rearrangement of this unusual microstructure results in ultra-high strength as well as increased ductility, which is not common, as normally solid materials tend to be brittle says Chen. Compared to a classic metal casting, ” we achieved almost triple strength and not only did we not lose ductility, but even increased it simultaneously “, he adds. “For many applications, a combination of strength and ductility is essential. Our results are original and exciting, both for materials science and engineering. »
” The ability to produce strong and ductile HEAs means that these 3D printed materials are more robust to resist applied deformations, which is important for the design of lightweight structures to improve mechanical efficiency and energy savings. “, Explain Jie RenChen’s doctoral student and first author of the paper.
The team developed computational dual-phase crystal plasticity models to understand the mechanistic roles played by FCC and BCC nanolamellae and how they work together to give the material increased strength and ductility.
” Our simulation results show the surprisingly high strength and hardening responses of BCC nanolamellae, which are essential to achieve the exceptional synergy between strength and ductility of our alloy. This mechanistic understanding provides an important basis to guide the future development of 3D-printed HEAs with exceptional mechanical properties. says Zhu.
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