Concentration threshold of yttrium addition on glass-forming ability and mechanical properties of ZrCuNiAlAg bulk metallic glass

The influence of Yttrium (Y) microalloying on the glass-forming ability (GFA), thermal stability, microstructural evolution, and mechanical properties of a Zr 55 Cu 29.5 Ni 5 Al 10 Ag 0.5 bulk metallic glass (BMG) was systematically investigated through a combination of experimental methods and first-principles calculations. A distinct concentration-threshold effect was observed. Low Y additions (0.5 at%) significantly enhanced the GFA (critical diameter increased from 6 mm to 10 mm) and thermal stability (supercooled liquid region ΔT widened from 35 K to 41 K), primarily attributed to Y's efficient oxygen-scavenging role. First-principles calculations revealed that Y preferentially forms Y-O short-range order with a 34.5 % reduced bond length (5.15 Å), stabilizing the amorphous structure against crystallization. Correspondingly, hardness, elastic modulus, and compressive yield strength peaked at 0.5 at% Y ( σ = 1783 MPa). However, higher Y concentrations (> 0.5–0.8 at%) led to a decrease in GFA, thermal stability, and mechanical strength ( σ dropped to 1713 MPa at 1.0 at% Y). This degradation correlates with the formation and coarsening (> 1 μm) of crystalline Y 2 O 3 precipitates, which was confirmed by SEM/TEM. Density functional theory calculations indicated Y 2 O 3 is significantly stiffer than the matrix, with an elastic modulus of 109 GPa, hardness of 7.43 GPa, and compressive strength of 1783.5 MPa. However, excessive Y doping (≥ 0.8 at%) induces coarsening of micron-scale precipitates, leading to structural heterogeneity and mechanical degradation. The study elucidates the dual role of Y: beneficial atomic-level purification and stabilization at low levels versus detrimental microstructural coarsening at higher levels. It establishes an optimal concentration of approximately 0.5 at% Y and provides insights for designing high-performance rare earth-doped BMGs. • An optimal Y concentration of ∼0.5 at% maximizes the glass-forming ability and mechanical properties. • Y 2 O 3 coarsening above 0.8 at% Y lead to decreased glass-forming ability and mechanical properties. • Enhanced glass-forming ability and thermal stability are attributed to the effective oxygen scavenging by Y addition. • First-principles calculations confirm the preferential formation of Y-O short-range order and the strengthening effect of Y 2 O 3 .