Silicon-Modified Ti-Based Refractory High Entropy Alloys for Enhanced Strength and Reduced Density

This study examines the effect of silicon (Si) addition on the microstructure, mechanical properties, and corrosion behavior of Ti₄Al₁.₅Cr₁.₅V₁.₅Nb₁.₅Si_x (x = 0–0.75 atomic ratio) refractory high-entropy alloys (RHEAs) synthesized via vacuum arc melting. The base alloy exhibited a single-phase BCC structure, while Si addition promoted the formation of hard M₅Si₃ silicide. At 0.25 Si, the alloy achieved superior mechanical performance, with enhanced strength and ductility resulting from solid solution strengthening, grain refinement, and fine silicide dispersion. However, higher Si contents (0.50 and 0.75) led to increased brittleness due to coarse silicide growth and elemental segregation. Corrosion resistance improved initially due to stable passive film formation but deteriorated at higher Si levels owing to micro-galvanic effects and structural inhomogeneity. These results highlight that optimized Si incorporation (x = 0.25) offers a strategic pathway to develop lightweight, high-strength RHEAs with balanced mechanical integrity and corrosion resistance for extreme service environments.