Chemically Gradient Ordered Nanodomains Enable Large Tensile Ductility in Gigapascal Lightweight Refractory...

High-strength lightweight refractory alloys are vital components serving in harsh environments with high mechanical loads at elevated temperatures, e.g., in aero-engines and hypersonic vehicles. Despite the long-term efforts on strengthening these materials, they usually show low ductility, particularly at room temperature, severely limiting their practical applications. Here, we introduce a concept to design extraordinarily ductile high-strength lightweight refractory high-entropy alloys (RHEAs) by introducing dispersed chemically gradient ordered nanodomains (CGONs, 1-3 nm) coherent with the disordered matrix. Chemical composition of the shell in the CGON is similar to that of the adjacent disordered matrix, and it varies gradually from the shell to the core. Such architecture not only enhances the thermodynamic stability of the CGONs but also facilitates stress transfer across the interfaces by reducing interfacial strain energy. The concept is realized in an Nb-Zr-Ti-Ta-Al RHEA system showing low mass density of 6.48 g/cm³, large uniform tensile elongation of 21.5%, elongation-to-failure of 47.8%, and high yield strength exceeding 1.0 GPa at room temperature. Further, the enhanced thermal stability of the CGONs contributes to the excellent high-temperature performance of the lightweight RHEA. The provided insights are thus important in guiding the development of ductile and ultra-strong lightweight refractory materials for key engineering applications.