Advancing the mechanical performance of chemically complex alloys through strategically engineered bamboo-inspired multi-stage heterostructures

Innovative design in heterostructure materials has emerged as a pivotal strategy to address the strength-ductility trade-off in metals and alloys. Inspired by the hierarchical structures found in bamboo, this study engineered a bamboo-like heterogeneous microstructure in a (FeCoNi)86Al7Ti7 chemically complex alloy (CCA) through a multi-step thermomechanical processing route. The bio-inspired triple heterostructures, featuring hierarchical grain sizes and multiscale, multi-morphology precipitates, significantly enhance the balance between strength and ductility, achieving nearly 2 GPa ultra-high tensile strength while maintaining good uniform plastic deformation. During deformation, L12 nanoprecipitates contribute to precipitation strengthening through the shear mechanism, while L21 submicron precipitates within the grains do so via the Orowan looping mechanism. L21 precipitates at the grain boundaries (GBs) act as reinforcement phases in the composite material. The bamboo-like heterostructure also alters dislocation accumulation by constraining deformation between coarse and ultrafine grains, influenced by the surrounding ultrafine grains and the diverse behaviors of precipitates. This pronounced back-stress strengthening across the matrix significantly enhances the strain-hardening capacity, thereby ensuring uniform plastic deformation. Overall, this novel approach demonstrates superior mechanical properties and offers a promising strategy for overcoming the strength-ductility trade-off in advanced alloys.