A diffuse-interface model for microstructure with an arbitrary number of components and phases was developed from basic thermodynamic and kinetic principles and formalized within a variational framework. The model includes a composition gradient energy to capture solute trapping, and is therefore suited for studying phenomena where the width of the interface plays an important role. Derivation of the inhomogeneous free energy functional from a Taylor expansion of homogeneous free energy reveals how the interfacial properties of each component and phase may be specified under a mass constraint. A diffusion potential for components was defined away from the dilute solution limit, and a multi-obstacle barrier function was used to constrain phase fractions. The model was used to simulate solidification via nucleation, premelting at phase boundaries and triple junctions, the intrinsic instability of small particles, and solutal melting resulting from differing diffusivities in solid and liquid. The shape of metastable free energy surfaces is found to play an important role in microstructure evolution and may explain why some systems premelt at phase boundaries and phase triple junctions while others do not.
Leveraging rapid sintering to retain metastable zirconia in copper
Nanyang Technological University（南洋理工大学）；Shanghai Jiao Tong University（上海交通大学）；Singapore Centre for 3D Printing, Nanyang Technological University（南洋理工大学三维打印中心）；Department of Civil Engineering, TongJi ZheJiang College（同济大学浙江学院土木工程系）
Exploration of the Microstructure Space in TiAlZrN Ultra-Hard Nanostructured Coatings
Ti $_{1-x-y}$ Al $_{x}$ Zr $_{y}$ N立方合金在25-70\% Al成分范围内由于高温下的亚稳相变途径而具有高的时效硬化能力。因此，它们是超硬纳米涂层材料的理想候选者。越来越多的证据表明，这种效果与弹性化学场诱导的相分离成成分分离的纳米立方氮化物相有关。在这里，我们研究了在1200 $^\circ$ C的调幅区域内的伪三元系的微观结构的演变，通过使用弹性化学相场模型。我们的模拟表明，氮化物纳米畴之间的弹性相互作用不仅极大地影响微观结构的形态，而且局部化学相平衡。在富铝区域的组合物空间中，我们进一步观察到富AlN相转变成其平衡纤锌矿晶体结构的发病。这项工作指出了这些氮化物系统可能获得的广泛的微观结构，并且它们的定制可能导致过渡金属氮化物基涂层材料的性能的显着改善。
Severe plastic deformations, mechanochemistry, and microstructure evolution under high pressure: In Situ Experiments, Four-Scale Theory, New Phenomena, and Rules
