The Mg-Y-Zn magnesium alloy system is commonly recognized for its remarkable combination of high strength and ductility, achieved even with minimal amounts of alloying elements. This exceptional performance is attributed to its unique microstructure, which includes Long-Period Stacking Ordered (LPSO) phases or the distinctive microstructure derived from the LPSO phase, referred to as the Mille-Feuille structure (MFS). This study systematically compares the traditional ingot metallurgy method with the rapid solidification technique, coupled with diverse heat treatments and extrusion processes. Microscopic analyses reveal variations in the presence of LPSO phases, Mille-Feuille structure, and grain size, leading to divergent mechanical and corrosion properties. The rapid solidification approach stands out, ensuring superior mechanical properties alongside a reasonable corrosion rate.
The near-rapid solidification conditions during additive manufacturing can lead to selection of non-equilibrium phases. Sharp interface models via interface response functions have been used earlier to explain the microstructure selection under such solidification conditions. However, most of the sharp interface models assume linear superposition of contributions of alloying elements without considering the non-linearity associated with the phase diagram. In this report, both planar and dendritic Calphad coupled sharp interface models have been implemented and used to explain the growth-contro…
Rapid solidification leads to unique microstructural features, where a less studied topic is the formation of various crystalline defects, including high dislocation densities, as well as gradients and splitting of the crystalline orientation. As these defects critically affect the material's mechanical properties and performance features, it is important to understand the defect formation mechanisms, and how they depend on the solidification conditions and alloying. To illuminate the formation mechanisms of the rapid solidification induced crystalline defects, we conduct a multiscale modeling…
We present a mathematical formulation of a multiscale model for solidification with convective flow in the liquid phase. The model is an extension of the dendritic needle network approach for crystal growth in a binary alloy. We propose a simple numerical implementation based on finite differences and step-wise approximations of parabolic dendritic branches of arbitrary orientation. Results of the two-dimensional model are verified against reference benchmark solutions for steady, unsteady, and buoyant flow, as well as steady-state dendritic growth in the diffusive regime. Simulations of equia…
Enhanced mechanical properties and microstructural stability of ultrafine-grained biodegradable Zn-Li-Mn-Mg-Cu alloys produced by rapid solidification and high-pressure torsion
In this article, we combine casting experiments and quantitative simulations to present a novel multiscale modeling approach to predict local primary dendritic spacings in metallic alloys solidified in conditions relevant to industrial casting processes. To this end, primary dendritic spacings were measured in instrumented casting experiments in Al-Cu alloys containing 1\,wt\% and 4\,wt\% of Cu, and they were compared to spacing stability ranges and average spacings in dendritic arrays simulated using phase-field (PF) and dendritic needle network (DNN) models. It is first shown that PF and DNN…
The solidification behavior of a eutectic AlCu specimen is investigated via in situ scanning transmission electron microscope (STEM) experiments. Solidification conditions are varied by imposing various cooling conditions via a micro-electro-mechanical system (MEMS) based membrane. The methodology allows the use of material processed by a melting and casting route close to industrial metallurgically fabricated material for in situ STEM solidification studies. Different rapid solidification morphologies could be obtained solely on a single specimen by the demonstrated strategy. Additional post-…
Quantitative Phase Field Model of Alloy Solidification
我们提出了一个详细的推导和薄界面分析相场模型，可以准确地模拟微观结构的斑图形成的低速定向凝固的稀二元合金。相对于先前的相场模型的这一进步是通过在质量守恒关系中添加唯象的“反捕获”溶质流来实现的[A。Karma，Phys. Rev. Lett 87，115701（2001）]。这种反捕获电流抵消物理，虽然人为的大，溶质捕获效应时产生的介观界面厚度被用来模拟实验长度和时间尺度上的界面演变。此外，当固体和液体中的扩散率不相等时，它在模型中提供了额外的自由度，以抑制与该厚度成比例的其他虚假效应[R. F. Almgren，SIAM J. Appl. Math 59，2086（1999）]，其包括表面扩散和对Stefan条件的曲率校正。这种自由度也可以用来使界面的动力学过冷度任意小，甚至对于界面厚度和相场弛豫时间的介观值也是如此，就像对于纯熔体的凝固一样[A.卡玛和W J. Rappel，Phys.Rev.E53，R3017（1996）]。该模型的性能表明，通过精确计算的第一次内的相场方法的Mullins-Sekerka稳定性谱的平面界面和非线性细胞的形状为现实的合金参数和生长条件。
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…
We investigated the homogenous nucleation of the stoichiometric B2 and B33 phases in the Ni50Zr50 alloy using the persistent embryo method and the classical nucleation theory. The two phases become very close competitors at large supercoolings, which is consistent with the experimental observations. In the case of the B2 phase, the linear temperature dependence of the solid-liquid interface (SLI) free energy extrapolated to the melting temperature leads to the same value as the one obtained from the capillarity fluctuation method (CFM). In the case of the B33 phases, the SLI free energy is als…
Phase-field modeling of microstructural pattern formation during directional solidification of peritectic alloys without morphological instability
在包晶合金定向凝固过程中，两个稳定的固相（母相和包晶相）竞争生长成亚稳液相，其杂质含量大于任何一个固相。当母相或两个固相在形态上不稳定时，即，对于小的温度梯度/生长速率比（$G/v_p$），一个固相通常生长出并覆盖另一个相，导致与在稀二元合金的单相凝固过程中形成的胞状-枝晶阵列结构非常类似的胞状-枝晶阵列结构。相反，当$G/v_p$大到足以使两相形态稳定时，微结构的形成受到两个固相的成核和生长之间的微妙相互作用的控制。在这种情况下观察到的结构（在对流效应被抑制的小样品中）包括垂直于生长方向的母相和周相的交替层（带），其通过一个相交替成核和横向扩散到另一个相上而形成，如最近的模型[R. Trivedi，Metall. Mater. A 26，1（1995）]，以及部分填充的带（岛），其中周晶相不完全覆盖连续生长的母相。我们开发了一个相场模型，结合成核过程，以探索这些结构的形成的周向凝固。该模型的模拟揭示了从岛屿到乐队的形态过渡，在母相上的成核后，这原来是由一个显着的恒定的加速度，和生长形态的类型，人们可能会期望在纯扩散生长条件下观察到的大样品的周边相的传播的动态。
Microstructure evolution during rapid solidification of hypoeutectic Al-Ag alloys near absolute stability
Colorado School of Mines（科罗拉多矿业学院）；Northeastern University（东北大学）；Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）
We introduce a new phase-field formulation of rapid alloy solidification that quantitatively incorporates nonequilibrium effects at the solid-liquid interface over a very wide range of interface velocities. Simulations identify a new dynamical instability of dendrite tip growth driven by solute trapping at velocities approaching the absolute stability limit. They also reproduce the formation of the widely observed banded microstructures, revealing how this instability triggers transitions between dendritic and microsegregation-free solidification. Predicted band spacings agree quantitatively w…
The superite phase and phase transition inducing multiscale solidification microstructures and segregations in steels
Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences（中国科学院金属研究所）；Department of Materials Science and Engineering, University of Science and Technology Liaoning（辽宁科技大学材料科学与工程学院）；Shanghai Synchrotron Radiation Facility (SSRF), Shanghai Advanced Research Institute, Chinese Academy of Sciences（中国科学院上海高等研究院）
Solute trapping is an important phenomenon in rapid solidification of alloys, for which the continuous growth model (CGM) is a popular sharp interface theory. Using matched asymptotic analysis, we show how to quantitatively map the sharp interface behavior of a binary alloy phase field model onto the CGM kinetics of Aziz et al. [1], with a controllable partition coefficient k(V ). We demonstrate the parameterizations that allow the phase field model to map onto the corresponding CGM or classical sharp interface models. We also demonstrate that the mapping is convergent for different interface …
A thorough understanding of pattern selection is necessary for the control of solidification structures, which are dissipative structures created by irreversible processes. In this paper, we simulate solidification evolution with different Preferred Crystallographic Orientations (PCOs) through the Phase-Field model. Then we study the effect of solute segregation on the interface energy, as well as the influence of the interface energy on the pattern selection. At the initial stage, the solute segregation influences the interface energy, determining the instability of the planar interface. Duri…
Element-Specific Solute Trapping and Grain Structure Evolution during Laser Powder Bed Fusion of Multicomponent Alloys
University of Michigan, Dearborn（密歇根大学迪尔伯恩分校）；Texas A&M University（德克萨斯农工大学）；AlphaSTAR Technology Solutions（AlphaSTAR技术解决方案）；University of Michigan, Ann Arbor（密歇根大学安娜堡分校）
The susceptibility of nickel-based superalloys to processing-induced crack formation during laser powder-bed additive manufacturing is studied. Twelve different alloys -- some of existing (heritage) type but also other newly-designed ones -- are considered. A strong inter-dependence of alloy composition and processability is demonstrated. Stereological procedures are developed to enable the two dominant defect types found -- solidification cracks and solid-state ductility dip cracks -- to be distinguished and quantified. Differential scanning calorimetry, creep stress relaxation tests at 1000$…
Phase-field models of microstructural pattern formation during alloy solidification are commonly solved numerically using the finite-difference method, which is ideally suited to carry out computationally efficient simulations on massively parallel computer architectures such as Graphic Processing Units. However, one known drawback of this method is that the discretization of differential terms involving spatial derivatives introduces a spurious lattice anisotropy that can influence the solid-liquid interface dynamics. We find that this influence is significant for the case of polycrystalline …
Additive manufacturing (AM) processes produce parts with improved physical, chemical, and mechanical properties compared to conventional manufacturing processes. In AM processes, intricate part geometries are produced from multicomponent alloy powder, in a layer-by-layer fashion with multipass laser melting, solidification, and solid-state phase transformations, in a shorter manufacturing time, with minimal surface finishing, and at a reasonable cost. However, there is an increasing need for post-processing of the manufactured parts via, for example, stress relieving heat treatment and hot iso…
Additive manufacturing (AM), through directed energy deposition, supports planned composition changes between locations within a single component, allowing for functionally graded materials (FGMs) to be developed and fabricated. The formation of deleterious phases along a particular composition path can cause significant cracking during the AM build process that makes the composition path unviable to produce these FGMs, but it is challenging to predict which phases will be present in as-built additively manufactured parts by analyzing only equilibrium phase relations. Solute segregation during…
