Thermally enhanced mechanical properties of arc evaporated Ti 0.34 Al 0.66 N / TiN multilayer coatingsIn contrast to the monolithic c-Ti 1Àx Al x N, the isostructural spinodal decomposition to c-AlN and c-TiN in c-Ti 1Àx Al x N/TiN multilayers has almost the same onset temperature for the compositions x ¼ 0.50 and 0.66. Differential scanning calorimetry also shows that the decomposition initiates at a lower temperature compared to the monoliths with the same Al-content. Z-contrast scanning transmission electron microscopy imaging reveals a decomposed structure of the multilayers at temperatures where the monoliths remain in solid solution. In the multilayers, the decomposition is initiated at the internal interfaces. The formation of an AlN-rich layer followed by a TiN-rich area parallel to the interface in the decomposed Ti 0.34 Al 0.66 N/TiN coating, as observed in atom probe tomography, is consistent with surface directed spinodal decomposition. Phase field simulations predict this behavior both in terms of microstructure evolution and kinetics. Here, we note that surface directed spinodal decomposition is affected by the as-deposited elemental fluctuations, coherency stresses, and alloy composition. V C 2013 American Institute of Physics. [http://dx.
A multicomponent and multiphase model with fluid motion is developed. The model is used to study reactive wetting in the case where concentration change of the spreading liquid and the substrate occurs. With the introduction of a Gibbs energy functional, the governing equations are derived, consisting of convective concentration and phase-field equations which are coupled to the Navier-Stokes equations with surface tension forces. The solid substrate is modeled hydrodynamically with a very high viscosity. Arbitrary phase diagrams, surface energies, and typical dimensionless numbers are some input parameters into the model. An axisymmetric model with an adaptive finite element method is utilized. Numerical simulations were done revealing two stages in the wetting process. First, the convection-dominated stage where rapid spreading occurs. The dynamics of the wetting is found to match with a known hydrodynamic theory for spreading liquids. Second, the diffusion-dominated stage where we observed depression of the substrate-liquid interface and elevation of the contact line region.
This work is dedicated to simulate the spinodal decomposition of Fe-Cr bcc (body centered cubic) alloys using the phase field method coupled with CALPHAD modeling. Thermodynamic descriptions have been revised after a comprehensive review of information on the Fe-Cr system. The present work demonstrates that it is impossible to reconcile the ab initio enthalpy of mixing at the ground state with the experimental one at 1529 K using the state-of-the-art CALPHAD models. While the phase field simulation results show typical microstructure of spinodal decomposition, large differences have been found on kinetics among experimental results and simulations using different thermodynamic inputs. It was found that magnetism plays a key role on the description of Gibbs energy and mobility which are the inputs to phase field simulation. This work calls for an accurate determination of the atomic mobility data at low temperatures.
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