Mechanism of solid-state reaction for fabrication of new glassy V45Zr22Ni22Cu11 alloy powders and subsequent consolidation

摘要

A single glassy phase of V45Zr22Ni22Cu11 alloy powders was synthesized by milling the elemental alloying powders in an argon atmosphere using a low-energy ball-milling technique. During the early and intermediate stages of milling, the atoms of Zr, Ni, and Cu migrated and diffused into the V (base material) lattice to form a body-centered-cubic (bcc) solid-solution, which transformed into a glassy phase with the same composition upon annealing at 850 K for 300 s in an argon atmosphere differential scanning calorimeter (thermally-enhanced glass formation reaction). As the milling time increased, the powders were subjected to continuous defects and lattice imperfections that led to a gradual change in the free energy so that solid-solution phase was transformed (mechanically enhanced glass formation reaction) to another metastable phase (glassy). Toward the end of the milling processing time, the bcc solid-solution transformed completely into a single glassy phase with the same composition. The glass-transition temperature, the crystallization temperature, and the enthalpy change of crystallization of the fabricated glassy powders were 741 K, 884 K, and -2.18 kJ/mol, respectively. This fabricated glassy alloy showed a wide supercooled liquid region (143 K) of metallic glassy alloy. The glassy powders were compacted in an argon gas atmosphere at 864 K with a pressure of 780 MPa using a hot-pressing technique. The consolidated sample was fully dense (above 99.2%) and maintained its chemically homogeneous glassy structure. The Vickers microhardness of the consolidated glassy V45Zr22Ni22Cu11 alloy was measured and found to be in the range between 6.89 GPa to 7.02 GPa. [References: 46]