Glass Formation In Cu Research Articles

Unequal effect of thermodynamics and kinetics on glass forming ability of Cu–Zr alloys

The glass forming ability (GFA) of Cu–Zr alloys has been still ambiguous, due to incomplete or lacking thermophysical properties of Cu–Zr liquids in supercooled and stable states, although tremendous effort has been devoted. We provide here the comprehensive thermophysical properties of Cu–Zr liquids, such as undercoolability, density, viscosity, fusion enthalpy, temperature–time-transformation (TTT) diagram, and crystal–liquid interfacial free energy. Three compositions, Cu64Zr36, Cu56Zr44, and Cu50Zr50, show distinctive anomalies in undercoolability, nose time in TTT, and crystal–liquid interfacial free energy, but not in density and viscosity in supercooled and stable liquid states. The anomalies reflect that the GFA is dominantly governed by thermodynamics rather than kinetics in these bulk metallic glasses (BMGs). In addition, we find that positions of nose temperatures in the TTT curves are below 1/2 (Tg + Tl), which implies unequal contribution of thermodynamics and kinetics. We discuss that empirical GFA parameters cannot explain the glass formation of Cu–Zr alloys due to the unequal contribution, and the Turnbull GFA criterion (Trg = Tg/Tl) is valid for the equal contribution of the two effects. The present experimental findings shed light on the ongoing debate about the GFA criterion of Cu–Zr BMGs.

Experimental and molecular dynamics simulation study on the glass formation of Cu–Zr–Al alloys

Alloys based on Cu–Zr–Al are known for their relative easiness in producing glassy structures. However, several important aspects related to the microstructure and the Glass Forming Ability (GFA) are still not well understood. Here, we present results referring to Molecular Dynamics simulations (MD) of rapidly quenched glassy Cu–Zr–Al of two compositions. GFAs were investigated, both experimentally and by MD simulations, using x-ray diffraction, High-Resolution Transmission Electron microscopy and Differential Scanning Calorimetry, while the structural evolution upon cooling was investigated by simulations using radial distribution functions, Voronoi tessellation analysis, and volume–temperature curves. Moreover, the viscosity evolution as well as the glass transition temperature and the fragility parameters were also estimated. Good agreement was found between the MD simulation results and the experimental data. It came out that the Zr–rich composition resulted in a ‘stronger’ metallic liquid than the Cu–rich composition. In addition, we found that the evolution of distorted into well shaped icosahedral clusters upon solidification, is a determining factor for the stability of the Zr–rich metallic glass. Moreover, we propose a new criterion based on a weighted average of the atomic radius ratio that has been found promising in adequately predicting glass forming abilities.

Metallic glass formation in Cu–Ni–Ti (Zr, Hf) systems studied by thermodynamic calculations

The glass formation regions for the family of Cu–Ni–Ti (Zr, Hf) systems have been calculated. The composition dependence of the glass forming ability was predicted and discussed in terms of the mixing enthalpy and atomic size effect.

Prediction of Bulk Metallic Glass Formation in Cu–Zr–Ag–Hf System by Thermodynamic and Topological Modeling

Cu based bulk metallic glasses (BMGs) are widely studied because of their high glass forming ability (GFA) and interesting combination of properties such as high strength coupled with good ductility and low cost. With these attributes, Cu based BMGs are being projected as promising materials for practical applications. The process of glass formation in metallic systems is a challenging task and alloys should be cooled from the liquid state at rates faster than a critical cooling rate (Rc) to resist crystallization. Interestingly, composition plays an important role in achieving easy glass formation, which is usually measured in terms of Rc. In the present work, attempt has been made to identify the composition for easy glass formation in Cu based quaternary system by theoretical approach. A GFA parameter PHS, which is a product of enthalpy of chemical mixing (∆Hchem) and mismatch entropy normalized with Boltzmann’s constant (∆Sσ/kB) is used to identify the best glass forming composition in Cu–Zr–Ag–Hf system. Further, a new parameter PHSS, which is a product of PHS and configurational entropy (ΔSconfig/R) is found to illustrate strong correlation with GFA. An attempt has also been made to correlate PHSS parameter with critical diameters and Rc using reported data in Cu–Zr–Ag–Hf system.

Bulk metallic glass formation in Cu–Zr–Ti ternary system

The formation of bulk metallic glasses (BMG) in the Cu-rich Cu–Zr–Ti ternary system is studied by using the ‘e/a-variant line criterion’. Three such lines, (Cu9Zr4)1−xTix, (Cu61.8Zr38.2)1−xTix and (Cu56Zr44)1−xTix, are defined in the Cu–Zr–Ti system by linking three binary compositions Cu9Zr4, Cu61.8Zr38.2 and Cu56Zr44 to the third element Ti. The binary compositions Cu9Zr4, Cu61.8Zr38.2 and Cu56Zr44 correspond to specific Cu–Zr binary clusters. BMGs are obtained by copper mould suction casting method with Ti contents of 7.5–15at.%, 7.5–12.5at.% and 5–12at.%, respectively along the (Cu9Zr4)1−x Tix, (Cu61.8Zr38.2)1−xTix and (Cu56Zr44)1−xTix lines. The BMGs on each composition line manifest decreased thermal stabilities and glass forming abilities (GFAs) with increasing Ti contents. The maximum GFA appears at Cu64Zr28.5Ti7.5, with characteristic thermal parameters of Tg=736K, Tx=769K, Tg/Tl=0.627 and γ=0.403, which are all superior to those reported for the known Cu60Zr30Ti10 BMG.

Cu–Zr–Al (Ti) bulk metallic glasses: Cluster selection rules and glass formation

The present paper investigates the bulk metallic glass formation in Cu–Zr–Al and Cu–Zr–Ti ternary systems by using the cluster line criterion. The binary basic clusters are first selected for constructing cluster lines. Three cluster selection rules are proposed: topologically dense packing, chemical short-range order and composition distance to deep eutectics. Three Cu–Zr clusters Cu 8Zr 5, Cu 6Zr 5 and Cu 5Zr 6 are selected according to the three rules. The bulk metallic glass-forming ranges in these two systems are determined. The thermal characteristic parameters of the Cu–Zr–Al BMGs on every composition line increase with increasing Al content and decrease with increasing Ti content in the Cu–Zr–Ti glass-forming range. The optimum bulk amorphous compositions in the Cu–Zr–Al system are Cu 58.1Zr 35.9Al 6 and Cu 39.7Zr 47.1Al 13.2, respectively, located in Cu 8Zr 5–Al and Cu 5Zr 6–Al cluster lines. In the Cu–Zr–Ti system, the Cu 64Zr 28.5Ti 7.5 composition with the largest T g/ T l is located in Cu 9Zr 4–Ti cluster line and the Cu 57.6Zr 32.4Ti 10 composition with the largest glass-forming ability is located in Cu 64Zr 36–Ti line.

Bulk metallic glass formation of Cu–Zr–Ti–Sn alloys

Cu–Zr–Ti–Sn bulk metallic glasses were produced by copper mold casting. The effects of Sn addition on glass-forming ability (GFA), thermal stability of the Cu 60Zr 30Ti 10 bulk metallic glass were investigated. It was found that a bulk metallic glass of 5 mm in diameter was prepared in a (Cu 60Zr 30Ti 10) 99Sn 1 alloy by copper mold casting. The addition of 1 at.% Sn is effective for an increase in GFA. The Δ T x and T g/ T l are 46 K and 0.63, respectively, for (Cu 60Zr 30Ti 10) 99Sn 1 alloy. With increasing the content of Sn, the value of T g/ T l increases, but the alloys begin to lose bulk metallic GFA. The new parameter γ has a better correlation with the GFA of the Cu-based alloys.