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

Abstract

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.