Designing refractory complex concentrated alloys for extreme environments

Abstract

The pursuit of advanced structural materials for use in extreme environments, specifically those exceeding 1200°C in aerospace, energy, and defense applications, has exposed the fundamental limitations of conventional Ni-based superalloys. In this context, refractory complex concentrated alloys (RCCAs) have emerged as a transformative materials paradigm, promising a unique combination of ultra-high temperature strength, exceptional microstructural stability, and superior creep resistance. This review provides a comprehensive and critical examination of the rapid advancements in the design and development of RCCAs. It begins by synthesizing the evolution of alloy design methodologies, tracing the progression from empirical and semi-empirical criteria to the integration of sophisticated computational tools, including computational thermodynamics (CALPHAD), first-principles calculations (DFT), and data-driven machine learning (ML) techniques for accelerated discovery. The discussion then delves into the microstructural engineering of RCCAs, highlighting architected phases such as coherent BCC/B2 nanocomposites that mimic the strengthening mechanisms of superalloys yet extend their operational ceiling. A thorough analysis of mechanical and environmental properties, encompassing strength-ductility synergies, creep, fatigue, and oxidation resistance, is presented, underscoring both remarkable achievements and enduring challenges, particularly in room-temperature ductility and long-term environmental durability. The review further assesses scalable manufacturing pathways, such as additive manufacturing, and identifies critical roadblocks to industrial scalability and adoption. By converging fundamental insights with advanced design and processing strategies, this review aims to chart a course for realizing the full potential of RCCAs as next-generation materials for the most demanding technological applications.