Innovative processing, microscopic properties, and entropy manipulation in refractory high entropy alloys

High-entropy alloys are metallic alloys composed of five or more principal elements in near-equiatomic ratios. Among them, refractory high-entropy alloys serve as the backbone of heavy engineering applications operating in extreme environments. These materials are crucial for advanced aerospace, defense, marine turbine blades, nuclear reactors, combustion chambers, and biomedical implants. This review provides a comprehensive analysis of refractory high entropy alloys, covering alloying methods, entropy manipulation, the impact of composition, thermo-mechanical properties, defect structures, and surface morphology based on experimental and theoretical tools. Herein, a special focus is given to factors responsible for failure and limitations in processing. In addition, we explore the key parameters influencing their macroscopic and microscopic properties using various microscopic, spectroscopic, and mechanical parameters. The real-world applications of refractory high-entropy alloys in heavy engineering, aerospace, biomedical, etc. are carefully discussed, emphasizing their superior mechanical performance, corrosion resistance, and biocompatibility. To enhance clarity, several flowcharts, schematic diagrams, and scientific images are incorporated, providing a detailed understanding of these advanced materials. Therefore, this review aims to bridge the gap between fundamental research and industrial applications, offering valuable insights into the potential of refractory high-entropy alloys for emerging technologies.