Interfacial instability of a planar interface and diffuseness at the solid-liquid interface for pure and binary materials
Yaw Delali Bensah, J. A. Sekhar
备注:
57 pages, 13 figures, 2 tables. Minor edits in abstract and main text. Some figures are compressed and one more figure added. A section on waveform is added
Topographical and diffuse interface reconfigurations occur with a change in the solidification rate. In this article we pursue the hypothesis that the interface configuration during solidification is determined by the rate of entropy production in the region between a rigorous solid and rigorous liquid phase. We posit that when an interface begins to migrate, there are several stable configurations that are possible. These include atomistically-planar, diffuse-planar, facet non-planar and cellular non-planar. The configuration and topographical condition that affords the maximum entropy production rate (MEPR) yields the most stable interface configuration. The principle of MEPR is applied to (1) describe atomistically smooth and diffuse interfaces, (2) provide quantitative results for the diffuse interface thickness and the number of pseudo-atomic layers in the interface region, and (3) predict the transition from planar to a non-planar facet or non-facet cellular morphology as a function of solidification velocity or temperature gradient. Numerous experimental investigations spanning over sixty years have failed to comprehensively validate any of the existing solid-liquid interface (SLI) growth instability models. With the MEPR model, for the first time, breakdown conditions are predicted with a fair degree of accuracy for a number of binary alloys where no previous theoretical model had predictability. The model considers steady state solidification at close-to and far-from equilibrium conditions.
Phase-Field Model with Reduced Interface Diffuseness
我们通过引入抛物型双阱势和将溶质再分布(或潜热释放)局部化到相场界面内的一个狭窄区域中,来最小化相场模型中的界面扩散。尽管该模型采用了带尖点的抛物型势、高度局部化的溶质再分布和不连续的扩散函数,但在数值计算中仍有很好的效果。对单侧系统枝晶凝固的计算与反陷阱模型[A. Karma,Phys. Rev. Lett. 87,115701(2001)],表明可以有效地抑制异常界面效应。该方法可以很容易地推广到多组分或多相体系。
By adjusting the interface energy, curvature, and velocity, the anisotropy plays an important role in the interaction between interfacial processes and transport processes, determining the solidification structures. In this paper, through the quantitative phase-field model, the influence of anisotropy on the evolution of interfacial morphologies in directional solidification is investigated. To represent different interfacial anisotropies, the solidification processes with different preferred crystallographic orientations are performed. Then the effect of anisotropy on morphological evolution …
This paper presents an efficient and quantitative phase-field model for elastically heterogeneous alloys that ensures the two mechanical compatibilities$\unicode{x2014}$static and kinematic, in conjunction with chemical equilibrium within the interfacial region. Our model contrasts with existing phase-field models that either violate static compatibility or interfacial chemical equilibrium or are computationally costly. For computational efficiency, the partial rank-one homogenization (PRH) scheme is employed to enforce both static and kinematic compatibilities at the interface. Moreover, inte…
Solidification structures are determined by the interaction between the interfacial processes and transport processes of heat and solute. In this paper, we investigate planar instability in directional solidification. Firstly, the interfacial evolution at the initial growth stage is simulated, indicating the planar instability is represented by the transition from the planar to the cellular. Secondly, to represent the history-dependence of solidification, constant thermal gradient G and varying pulling speed VP are used in the simulations. The results indicate the cooling rate R ( = G*VP) domi…
Using the first-principles non-equilibrium Green's function technique with supercell disorder averaging, we study the influence of interfacial intermixing on the spin-orbit torque in Co$\mid$Pt bilayers. Intermixing is modeled by inserting one or more monolayers of a disordered CoPt alloy between Co and Pt. Dampinglike torque is moderately enhanced by interfacial intermixing, while the fieldlike torque, which is small for abrupt interfaces, is strongly enhanced and becomes comparable to the dampinglike torque. The enhancement of the fieldlike torque is attributed to the interface between Co an…
A Molecular Approach for Engineering Interfacial Interactions in Magnetic-Topological Insulator Heterostructures
控制磁性/拓扑绝缘体异质结构中的界面相互作用是出现新的自旋相关电子现象的主要挑战。对于任何依赖邻近效应的异质结构的合理设计,理想情况下应该保留每个组件的整体属性,同时调整界面处的相互作用。然而,在大多数无机界面相互作用太强,因此扰动,甚至淬火,在界面的每一侧的磁矩和拓扑表面状态。在这里,我们表明,这些属性可以通过使用配体化学来调整磁性离子与表面状态的相互作用来保持。通过在Bi $_2$ Te $_3$薄膜的表面上沉积Co基卟啉和酞菁单层,形成了稳健的界面,其保留了未掺杂的拓扑表面状态以及二价Co离子的原始磁矩。所选择的配体允许我们在该弱相互作用范围内调节界面杂化。这些结果,这是在与Co酞菁的相互作用诱导的Bi $_2$ Se $_3$的第一个五重层的表面状态的观察到的抑制形成鲜明对比,证明了平面金属有机分子的能力,跨越从强到弱的限制的相互作用。
Spectral analysis of non-equilibrium molecular dynamics: spectral phonon temperature and phonon local non-equilibrium in thin films and across interfaces
Adsorption of liquid on a planar wall decorated by a hydrophilic stripe of width $L$ is considered. Under the condition, that the wall is only partially wet (or dry) while the stripe tends to be wet completely, a liquid drop is formed above the stripe. The maximum height $\ell_m(δμ)$ of the drop depends on the stripe width $L$ and the chemical potential departure from saturation $δμ$ where it adopts the value $\ell_0=\ell_m(0)$. Assuming a long-range potential of van der Waals type exerted by the stripe, the interfacial Hamiltonian model is used to show that $\ell_0$ is approached linearly wit…