Achieving excellent strength-toughness combination in hexagonal closed-packed multi-principle element alloys via (c plus a) slip promotion

To effectively bolster (c + a) slip is pivotal to improving the mechanical property of hexagonal close-packed (HCP) metallic materials. It has been a longstanding challenge facing the structural material community. Here we introduce a strategy to crack this hard nut. By employing two coarse-grained Ti-Zr-Hf model alloys as examples, we demonstrate for the first time that the two intrinsic properties of multi-principle element alloys (MPEAs)-high alloy concentration and local fluctuation-can work synergistically to narrow the gap in nucleation/gliding resistance between non-prismatic and prismatic slips, leading to enhanced activities of (c + a) and first order pyramidal (a) dislocations. This renders the material an exceptional strength-toughness combination, outperforming other coarse-grained HCP alloys and even rivalling most of those with delicately designed microstructrues including nanostructures and heterostructures. Given that high concentration and local fluctuation are intrinsic to all MPEAs, we anticipate that this strategy could be extended to other MPEAs featuring an HCP structure.