Compositional gradient structures in metallic materials: A review

Mechanical properties, particularly strength and ductility, are decisive for the performance and reliability of structural materials deployed in demanding service environments. Increasing a material’s strength is usually accompanied by a concomitant reduction in ductility. This intrinsic strength–ductility trade-off severely constrains the design space of metallic materials. In recent years, gradient-structured materials have shown remarkable promise in transcending this long-standing limitation by tailoring microstructures to activate synergistic deformation mechanisms. To date, most studies and reviews have centred on structural gradients, such as grain size, lamella thickness and twin spacing gradients. By contrast, compositional gradients represent an equally potent design route and have already attracted considerable attention. Nevertheless, no dedicated review of compositionally graded metallic materials is currently available. This article provides a systematic review of compositionally graded materials, with particular emphasis on fabrication methods, microstructural characteristics, deformation mechanisms, and the resulting strength–ductility synergy, as well as overarching design strategies. Our objective is to establish a comprehensive framework that can inform the future design and processing of next-generation metallic materials.