Liquid Thermophysical Properties and Crystalline–Amorphous Hybrid Microstructures of Quaternary Zr–Ni–Al–Nb Alloy Explored Under Electrostatic Levitation Condition

The thermophysical properties and rapid solidification mechanism of liquid Zr–25 at. pct Ni–15 at. pct Al–4 at. pct Nb alloy were investigated by electrostatic levitation (ESL) technique, which achieved a maximum undercooling up to 274 K (0.22 T_L). The density, surface tension and viscosity of this glass-forming alloy at its liquidus temperature were measured as 6.39 g cm⁻³, 1.47 N m⁻¹ and 107.75 mPa s, respectively. Experimental results and theoretical analyses confirmed the feasibility of controlling the formation of crystalline and amorphous phases by adjusting the liquid undercooling level, which provides new insights for optimizing the preparation processes of amorphous alloys. At undercoolings below 140 K, this alloy predominantly solidified into pseudobinary (Zr₆Al₂Ni + Zr₅Ni₄Al) plus pseudoternary (Zr₆Al₂Ni + Zr₅Ni₄Al + bct-Zr₂Ni) eutectics. Beyond 140 K undercooling, the crystalline region transformed into a mixture of fcc-Zr₂Ni phase and pseudobinary eutectics. At large undercoolings above 267 K, an amorphous phase appeared to form an amorphous–crystalline core–shell structure. The amorphous phase volume fraction increased gradually and attained 83 pct at the maximum undercooling. Both transmission electron microscopy and Voronoi analysis revealed a shared icosahedral short-range order between the metastable fcc-Zr₂Ni phase and the amorphous matrix, demonstrating how their structural continuity bridges metastable crystallization and glass formation by templating local atomic arrangements during rapid solidification.