Theoretical calculation of the melting curve of Cu-Zr binary alloys

Abstract

Helmholtz free energies of the dominant binary crystalline solids found in the Cu-Zr system at high temperatures close to the melting curve are calculated. Our theoretical approach combines fundamental measure density functional theory (applied to the hard-sphere reference system) and a perturbative approach to include the attractive interactions. The studied crystalline solids are Cu(fcc), Cu_{51}Zr_{14}(β), CuZr(B2), CuZr_{2}(C11b), Zr(hcp), and Zr(bcc). The calculated Helmholtz free energies of crystalline solids are in good agreement with results from molecular-dynamics (MD) simulations. Using the same perturbation approach, the liquid phase free energies are calculated as a function of composition and temperature, from which the melting curve of the entire composition range of this system can be obtained. Phase diagrams are determined in this way for two leading embedded atom method potentials, and the results are compared with experimental data. Theoretical melting temperatures are compared both with experimental values and with values obtained directly from MD simulations at several compositions.

Discovery of a Wide Variety of Linear Complexions in Face Centered Cubic Alloys

“…Three regions were identified corresponding to samples with (1) solute segregation but no phase transformation (black dots), (2) ordered complexion transformations (yellow circles) into stacking fault complexions, and (3) heterogeneous precipitation of a disordered phase (purple circles). The solid line in Figures 9(a) represents the bulk melting curve, obtained for the interatomic potential used in this work [49]. Finally, we confirm the existence of stacking fault linear complexions using a long simulation cell for Cu-1 at.% Zr equilibrated at 800 K. Figure 10 shows the perspective, top, and zoomed views of this system, where the stacking fault complexion transformation happens all along the dislocation line.…”

“…Ordered complexions are shown in yellow, while disordered complexions and bulk phases are shown in magenta. The solid black line represents the melting curve for Cu-Zr computed for the interatomic potential used in this work[49]. The dashed line was added to schematically demonstrate that the local compositions of ordered and disordered complexions can be separated from each other and do not overlap.…”

A self-contained algorithm for determination of solid-liquid equilibria in an alloy system

“…In addition, many phenomena of interest such as crystal nucleation and growth occur when the liquid becomes supercooled, when it behaves so differently from the ideal gas that one can hardly obtain the required accuracy by using the ideal gas as the starting point. Furthermore, it is generally not a good idea to treat the liquid and solid phases in separate frameworks when it is the free energy difference that controls phase stability [6]. Here, we construct an "alchemical" path to transform a pure liquid to a liquid alloy, and apply TI to evaluate the mixing enthalpy and entropy during the process.…”

Prediction of glass forming ability in Cu(x)Zr(1-x) alloys using molecular dynamics

“…T g and T l are calculated using WendtAbraham (WA) parameter [17] and volume temperature (V −T ) curve. The relationship between the melting temperature (obtained from the MD simulation) and experimental T l values have been correlated and compared with those reported previously [18,19].…”