Mitigating Strain Localization via Stabilized Phase Boundaries for Strengthening Multi-Principal Element Alloys.

Multi-principal element alloys (MPEA) demonstrate exceptional stability during rapid solidification, making them ideal candidates for additive manufacturing and other high-design-flexibility techniques. Unexpectedly, MPEA failure often mimics that of conventional metals, with strain localization along phase or grain boundaries leading to typical crack initiation. Most strategies aim at reducing strain localization either suppress the formation of high-energy sites or dissipate energy at crack tips to enhance toughness, rarely achieving a synergy of both. Inspired by the microstructure of mouse enamel, nanoscale body-centered cubic (BCC) and face-centered cubic (FCC) phases into MPEAs are introduced, stabilized at phase boundaries to provide ample plastic space for dislocation-mediated deformation. This approach overcomes the local hardening limitations of nanoscale alloys and harmonizes traditional toughening mechanisms-such as crack deflection, blocking, and bridging-to mitigate strain localization. These mechanisms impart the alloy with ultra-high tensile strength (≈1458.1 MPa) and ductility (≈21.2%) without requiring heat treatment. Atomic calculations reveal that partial atomic plane migration drives continuous dislocation transfer across phases. This study uncovers fundamental but latent mechanical mechanisms in MPEAs, advancing understanding of ultra-strong bioinspired alloys.