Embedded-atom-method effective-pair-interaction study of the structural and thermodynamic properties of Cu-Ni, Cu-Ag, and Au-Ni solid solutions

Atom Probe Study of the Miscibility Gap in CuNi Thin Films and Microstructure Development

The unclear miscibility of CuNi alloys was investigated with atom probe tomography (APT). Multilayered thin film samples were prepared by ion beam sputtering (IBS) and focused ion beam (FIB) shaping. Long-term isothermal annealing treatments in a UHV furnace were conducted at temperatures of 573, 623, and 673 K to investigate the mixing process. The effective interdiffusion coefficient of the nanocrystalline microstructure (including defect diffusion) was determined to be Deff = 1.86 × 10−10 m2/s × exp(−164 kJ/mol/RT) by fitting periodic composition profiles through a Fourier series. In nonequilibrium states, microstructural defects like grain boundaries and precipitates were observed. While at the two higher temperatures total mixing is observed, a clear experimental evidence is found for a miscibility gap at 573 K with the boundary concentrations of 26 and 66 at%. These two compositions are used in a subregular solution model to reconstruct the phase miscibility gap. So, the critical temperature TC of the miscibility gap is found to be 608 K at a concentration of 45 at% Ni.

Simulation on the Factors Affecting the Crystallization Process of FeNi Alloy by Molecular Dynamics

This paper investigates the crystallization process of FeNi alloys with different impurity concentrations of Ni(x) [x = 10% (Fe₉₀Ni₁₀), 20% (Fe₈₀Ni₂₀), 30% (Fe₇₀Ni₃₀), 40% (Fe₆₀Ni₄₀), and 50% (Fe₅₀Ni₅₀)] at temperature (T) = 300 K and Fe₇₀Ni₃₀ at heating rates of 4 × 10¹², 4 × 10¹³, and 4 × 10¹⁴ K/s at different temperatures, T = 300, 400, 500, 600, 700, 900, 1100, and 1300 K. Molecular dynamics models with the Sutton-Chen embedded interaction potential and recirculating boundary conditions are used to calculate the molecular parameters of alloys, such as radial distribution function, total energy of the system (E _tot), size (l), and crystallization temperature (through the relationship between E _tot and T). The common neighborhood analysis method is used to confirm the theoretical results of crystallization for Fe-Fe, Fe-Ni, and Ni-Ni. The annealing process did not have an effect on the crystallization process of FeNi alloys. The effect of Ni content, heating rate, and annealing time on structural unit numbers, such as face-centered cubic, hexagonal close-packed, blocked cubic center, and amorphous, and the crystallization process of FeNi alloys is also investigated.

A numerical coarse-grained description of a binary alloy

We employ Monte Carlo simulation in the semi-grand canonical ensemble to obtain the coarse-grained free energy corresponding to an embedded-atom method description of a binary alloy. In particular, the Ginzburg-Landau free energy for a Cu-Ni alloy was determined from a tabulated histogram of the joint probability density of composition, energy, and volume. Using histogram reweighting techniques, the free energy is extrapolated to a range of points in parameter space from a small number of simulations. The results are interpreted by comparing the free energy with that corresponding to a regular solution model of an alloy. In addition, we obtain expressions for thermodynamic quantities in terms of the joint cumulants of the probability density at a given temperature and chemical potential difference. These expressions may then be likewise extrapolated to obtain the dependence of the composition on the temperature and the chemical potential difference over a wide range of parameter space.

Competition between order and phase separation in Au-Ni

We have measured and theoretically analyzed the diffuse scattering in the binary alloy system Au-Ni, which has been proposed as a testing ground for theories of alloy phase stability. We found strong evidence that in the alloys Au3Ni and Au3Ni2, fluctuations of both ordering- and clustering-type are competing with each other. Our results resolve a long-standing controversy on the balance of relaxation and mixing energies in this alloy system and explain recent findings of ordering in thin Au-Ni films.

Strain-induced nonanalytic short-range order in the spin glass Cu(83)Mn(17)

We present a theoretical and experimental study of the effect of lattice distortions on the short-range order and the energetics of ordering binary alloys. Applying a reciprocal space approach which accounts for the elastic response of the lattice, the diffuse scattering of the model system Cu(83)Mn(17) can be explained with only a few physical parameters. The model calculations point to a nonanalytic diffuse intensity at q = 0. X-ray scattering experiments are presented providing clear evidence for this phenomenon which carries detailed information on the strain-induced interaction.