High-entropy alloys with heterogeneous microstructure: Processing and mechanical properties

Engineering metallic materials are an essential class of materials for a variety of industrial applications due to their competitive mechanical properties, especially strength and ductility. Metallic materials with excellent mechanical properties are highly sought-after as engineering materials for various applications considering safety, environmental, and economic requirements. Thus, the development of high-performance alloys with high strength and high ductility is an unfading research topic for material scientists. The strength enhancement in metallic materials by conventional strengthening mechanisms always leads to a reduction in ductility, which is often referred to as strength-ductility trade-off. In recent decades, novel approaches to enhance strength-ductility synergy through heterogeneous microstructures, such as gradient, harmonic, lamellar, bimodal, hierarchical nanostructures, etc., have been proven to be effective in overcoming strength-ductility trade-off. However, the alloy design concept of conventional alloys limits the exploration of new alloys with good strength-ductility synergy even through heterogeneous microstructures. The discovery of a new alloy design concept based on multi-principal elements, widely known as high entropy alloys, opens up a vast compositional space and offers wider possibilities to find numerous new alloys with remarkable properties. This review article presents an overview of the mechanical behavior of high entropy alloys with heterogeneous microstructures that reconcile the strength-ductility synergy.