Effect of structural heterogeneity on thermal, mechanical, and tribological properties of (Ti ₅₀ Zr ₅₀ ) <i> _x </i> (Ni ₃₃ Co ₃₃ Fe ₃₃ ) _{100− <i>x</i>} high-entropy bulk me

In this study, a series of (Ti 50 Zr 50 ) x (Ni 33 Co 33 Fe 33 ) 100− x high-entropy bulk metallic glasses (HE-BMGs), with x ranging from 30 to 70 at.%, were synthesized using vacuum arc melting followed by suction casting. The influence of compositional variation on phase formation, thermal stability, mechanical hardness, and tribological performance was systematically investigated. Thermodynamic parameters, including mixing enthalpy, configurational entropy, atomic size mismatch, and the Ω parameter, predicted strong glass-forming ability across all compositions. X-ray diffraction and differential scanning calorimetry confirmed fully amorphous structures with wide supercooled liquid regions (Δ T = 53.7–68.1 °C), indicating high thermal stability. Vickers microhardness decreased from 875.76 HV to 663.16 HV as Ti–Zr content increased, corresponding to an approximate 24% reduction in hardness. Tribological tests revealed that the specific wear rate increased from 7.76 × 10 −6 to 21.24 × 10 −6 mm 3 /Nm, while the coefficient of friction rose from 0.355 to 0.507 with increasing Ti–Zr content. Fe–Co–Ni-rich alloys exhibited superior wear resistance and lower friction. These results demonstrate that compositional balancing is critical for optimizing the mechanical and tribological performance of HE-BMGs for lightweight, wear-resistant structural applications.