Stability of Supercooled Liquid and Transformation Behavior in Zr-Based Glassy Alloys

Abstract

We investigated the stability of the supercooled liquid in Zr-based glassy alloys by examination of their transformation behavior. The primary phase is an fcc Zr 2 Ni phase in a Zr 65 Al 7.5 Ni 10 Cu 17.5 glassy alloy with high glass-forming ability (GFA). By substitution of Ag, Pd, Au or Pt for only 1 at%Cu, an icosahedral quasicrystalline phase (I-phase) precipitates with the fcc Zr 2 Ni phase. The primary phase changes to the single I-phase at higher noble metal contents. It is further found that the I-phase precipitates by a small amount of substitution for Cu with other elements as well as the noble metals, which have a weak or positive chemical affinity with one of the constitutional elements in the Zr-Al-Ni-Cu glassy alloy. Thus, the slight deviation from the three component rules for high GFA is effective for the I-phase formation. The I-phase is also formed as a primary phase in the Zr 65+y Al 7.5 Ni 10 Cu 17.5−y (y = 1-7) glassy alloys. A slight change in the composition has the similar effect as the addition of element such as noble metals and so on. An icosahedron is contained as a structure unit in the fcc Zr 2 Ni and I-phases and hence the glassy structure is correlated with the local icosahedral atomic configuration. The high-resolution transmission electron microscopy image of the Zr 70 Al 7.5 Ni 10 Cu 12.5 glassy alloy reveals a possibility of the existence of the icosahedral ordered regions. It is therefore, concluded that the icosahedral short-or medium-range order exists in the supercooled liquid as well as in the glassy phase and it stabilizes the supercooled liquid state in the Zr-based alloys. An I-phase also precipitates as a primary phase by substituting Pd, Au or Pt for only 1 at%Cu in the Zr 70 Cu 30 glassy alloy. From these results, the appearance of the supercooled liquid region is attributed to the existence of the icosahedral atomic configuration consisting of Zr and Cu.

Structural Relaxation in Supercooled Liquids

“…This point is supported both by the experiments 7,8) and the simulations. 9-11) Therefore, we investigate the local symmetry around the individual atoms by using the Voronoi polyhedra analysis, 12) and clarify the cluster structure with paying a special attention to the icosahedral clusters.…”

“…12(b) to experimental obsevations 15,16) of the ternary systems with similar combination of atomic size ratios, for example, the Cu-Al-Zr system and the Ni-Al-Zr Structural Relaxation in Supercooled Liquidssystem, in both of which a sign of the icosahedral order in the supercooled liquid phase and the glassy phase is experimentally observed. 8,17) Although our prediction is based on a quite simple model, in which only the atomic size effect is taken into account and the interaction is described by the twobody LJ potential, the main tendency of the GFA considerably agrees with the experimental results. It indicates that the atomic size effect should be the primary factor to acquire a high GFA in metallic systems.…”

Atomic structure in Zr70Ni30 metallic glass

“…5 Stability of MG is linked with its atomic structure, 6,7 which correlates with atomic structure of the corresponding crystalline phase by annealing. 8,9 For example, icosahedral clusters are found to be dominant atomic structure in Zr 70 Cu 29 Pd 1 MG, 10,11 which leads to primary phase transition by forming icosahedral quasicrystal 12,13 after annealing, while Zr 70 Ni 30−x Pd x ͑x Ͻ 10 at. % ͒ MGs do not exhibit such primary precipitation.…”

Synthesis and Fundamental Properties of Cu-Based Bulk Glassy Alloys in Binary and Multi-component Systems

“…It is well known that the icosahedral type short-range atomic configuration is one of the favorable glassy structures leading to enhancement of stability of the supercooled liquid against crystallization. 13) 3. Formation and Thermal Stability of Multi-component Bulk Glass Alloys respectively.…”