Melt convection plays a critical role in microstructure evolution during alloy solidification, yet accurately capturing its interaction with moving solid-liquid interfaces remains a significant computational challenge, particularly in multi-phase, multi-component systems. In this work, we develop a computational framework that couples a Grand-Potential phase-field model with the Lattice Boltzmann method (LBM) to simulate convection-driven solidification within a unified and thermodynamically consistent formulation. The proposed approach rigorously enforces no-slip conditions at evolving solid-liquid interfaces, while fluid transport is solved using the standard single-relaxation-time Bhatnagar-Gross-Krook collision operator. The framework provides an efficient and robust methodology for resolving the coupled evolution of interfaces, solute transport, and fluid flow. The versatility of the proposed framework is demonstrated through simulations of dendritic and eutectic solidification under natural convection. The results show that convection significantly modifies solute segregation, destabilizes growth fronts, and induces oscillatory growth modes in both systems. These examples illustrate the capability of the proposed method to capture complex flow-induced morphological instabilities and provide new insights into the mechanisms governing convection-driven microstructure evolution in alloy solidification.

Laser based additive manufacturing of gamma - gamma ' nickel-based superalloys usually involves a post-build heat treatment process to achieve required volume fraction and size distribution of the gamma ' precipitates. The presence of gamma ' in the as-built condition of the sample and micro-segregation at nanoscale could offer possibilities of shorter heat treatment protocols that avoid homogenization stage. In this study, we establish the presence of gamma ' precipitate (-8 nm with a volume fraction of 0.11 %) in the as-built sample of Haynes 282 alloy using high resolution transmission electron microscopy. Based on this observation, a modified heat treatment protocol is demonstrated to achieve uniform and fine distribution of gamma ' precipitates (-49 nm with a volume fraction of 18.2 %). This work establishes a pathway towards optimized and energy-efficient heat-treatment protocol for additively manufactured Haynes alloys.

Metal powder production through atomization has huge potential in the fabrication and repair industry. Employing atomized powders for a solid-state or low-temperature process, such as the cold spray technique, requires a suitable intrinsic microstructure to achieve the desired properties. Heat treatment of atomized powders can help achieve the desired microstructure for its intended application. The age-hardenable Al7075 alloy is used in the aerospace industry due to its highest strength among aerospace-grade Al alloys. Microstructure studies on as-received gas-atomized powder reveal dendritic structures with solute segregation at the interdendritic regions. The received powder was subjected to solutionization at 490 degrees C for up to 4 h. Upon solutionization of the powder, the dendritic structure disappeared, and the segregation of the solute is also reduced. Additionally, the solutionized powders were aged at 120 degrees C for different time intervals up to 48 h. Precipitation in Al7075 powder was studied by small-angle X-ray scattering (SAXS), and compared with that of bulk Al7075 alloy. SAXS studies confirm that the scattering amplitude and range were not affected by the solutionization time. The scattering was more widely distributed for Al7075 powder samples and narrower for bulk Al7075 alloy samples in aged condition. Moreover, conventional bulk alloy exhibits monodisperse size distribution, whereas powder samples exhibit polydispersity. Also, the volume fraction of GP zones phase (precipitates) is higher in bulk samples than in powder samples.

The mechanical properties of gamma/gamma' superalloys are governed by the size, shape, and distribution of the gamma' precipitates within the gamma matrix. This work explores the feasibility of microstructure tuning by varying cooling rates in a low mass density gamma/gamma ' Co-30Ni-10Al-2Nb-4Ti-12Cr (at %) superalloy. We observe a strong cooling rate dependence on the morphology, composition, shape, and size distribution of gamma ' precipitates. Cooling rates >= 6.25 K/s from super-solvus temperature (1413 K) of the alloy show unimodal size distribution of gamma ' precipitates with a high number density. Whereas a slower rate of cooling (<= 6.25 K/s) results in the formation of the bimodal size distribution of gamma ' precipitates. For all the cooling rates explored (100, 28, 6.25, 1.625, 0.43, and 0.108 K/s), secondary gamma ' precipitates exhibit nearly cuboidal morphology, and power law describes the evolution of their size with different cooling rates. Atomic-scale compositional analysis by an atom probe reveals the composition of secondary gamma ' precipitates is dependent on the cooling rates. In addition, we found finer tertiary gamma ' precipitates near the secondary gamma ' precipitates and matrix interface, while relatively larger tertiary gamma ' precipitates away from the secondary gamma ' precipitates for the slow cooling rates (1.625 K/s, and 0.108 K/s). This was attributed to the concentration gradient that develops in the gamma matrix region in between the secondary gamma' precipitates during continuous cooling. In the light of classical nucleation theory, the results indicate a multi-stage formation of gamma ' precipitates whose morphology, size distribution, and composition are found to be dependent on the cooling rates. Hence, these experiments shows the possibility of tuning the microstructure of Co-based superalloys that is critical in governing their mechanical properties.

In aerospace industries, optimisation of the welding process parameters is crucial to achieve high-performance welds in superalloy. The current study develops an integrated computational materials engineering (ICME) framework for the Electron Beam Welding (EBW) process optimisation of XH67MBT & YUcy; Ni-based superalloy. The thermal field was established using FEM simulation. The microstructure in the fusion zone was simulated using the phase field method and validated using experimental data. The Heat Affected Zone (HAZ) microstructure was predicted using kinetic calculation and validated using the physical simulation followed by experimental microstructural characterisation. The TEM studies confirm the formation of Cr-rich and Ti-rich carbides in the HAZ thermal cycle simulated samples. A hot ductility curve was established for the studied alloy, and this can guide the restraint condition for welding. Finally, an ICME framework is suggested and validated for the EB welding optimisation.

XH67MBTЮ superalloy is used extensively in aerospace applications and is subjected to various thermo-mechanical cycles. Weldability studies of these alloys are critical for their successful industrial application. The current study shows integrated micro- and macroscale simulation for optimising the welding process in the XH67MBTЮ alloy. The Gas Tungsten Arc welding process is simulated and validated with experimental results. The microstructure formation inside the fusion zone is simulated by the phase field method. The segregation of elements in the fusion zone is established and shows comparable results with experimental data. The inter-dendritic segregation of elements with respect to the varying solidification conditions was studied via phase field simulation. The Ti segregation map confirms that carbide formation can be modified while modifying welding conditions. The microstructure formation in the Heat Affected Zone (HAZ) is studied by integrating the thermal cycle from macroscale simulation, kinetic calculations and physical simulation. The TEM investigation of the HAZ physical simulated sample shows the formation of Ti-rich (MC type) and Cr-rich (M23C6 type) carbides. These studies will guide the weldability studies in XH67MBTЮ superalloy with limited experimental trials.

The phase-field method has become a useful tool for the simulation of classical metallurgical phase transformations as well as other phenomena related to materials science. The thermodynamic consistency that forms the basis of these formulations lends to its strong predictive capabilities and utility. However, a strong impediment to the usage of the method for typical applied problems of industrial and academic relevance is the significant overhead with regard to the code development and know-how required for quantitative model formulations. In this paper, we report the development of an open-source phase-field software stack that contains generic formulations for the simulation of multi-phase and multi-component phase transformations. The solvers incorporate thermodynamic coupling that allows the realization of simulations with real alloys in scenarios directly relevant to the materials industry. Further, the solvers utilize parallelization strategies using either multiple CPUs or GPUs to provide cross-platform portability and usability on available supercomputing machines. Finally, the solver stack also contains a graphical user interface to gradually introduce the usage of the software. The user interface also provides a collection of post-processing tools that allow the estimation of useful metrics related to microstructural evolution.

The electron beam welding (EBW) of a γ′ strengthened nickel-based superalloy, Haynes 282 (HY282), with austenitic stainless steel SS321, has applications in aerospace and advanced ultra-supercritical (AUSC) power plants. In this study, a dissimilar combination of materials, HY282 and SS321, were welded using EBW process. The convection in the weld pool and rapid solidification during EBW resulted in the formation of Fe- and Ni-rich bands throughout the weld pool. A standard two-step aging process for HY282 was performed on the weld, and its effects were studied using SEM and TEM analysis. These bands lead to the formation of an inhomogeneous distribution of γ′ within the weld after the two-step aging process. A FIB sample taken at the SS321 fusion boundary (FB) shows the presence of γ′ even with the enrichment of Fe and its size increased to 56nm at the FB. To study the effect of macrosegregation on the mechanical properties, microhardness survey and high-temperature tensile testing at 720 °C were performed. The hardness contour plots showed the correlation with the microstructural band. The hardness of HY282 increased from 220 to 320 HV after two-step aging, whereas SS321 exhibited a slight reduction to 140 HV, attributed to abnormal grain growth (AGG) during aging. The weld joint demonstrated superior high-temperature tensile strength at 720 °C compared to SS321, despite the presence of microstructural bands in the weld and liquation cracking in the HAZ of HY282. During high-temperature tensile testing, failure occurred in the SS321, with ultimate tensile strengths of 311 MPa in the as-welded condition and 285 MPa after aging.

Challenges such as build chamber size limitations, residual stress generation, and anisotropic properties associated with laser powder bed fusion (LPBF) in the fabrication of large structures can be mitigated using hybrid designs that integrate additively manufactured components with conventionally manufactured parts. The feasibility of such hybrid components will be proven through weldability. This study investigates microstructural changes occurring in keyhole TIG-welded samples of LPBF-manufactured and wrought Haynes 282 plates and the influence of welding on the mechanical properties of the resultant joint. The hybrid weldment exhibited higher tensile strength compared to the weldment made with wrought plates on both sides, and this finding was further supported by fatigue testing of the welded samples. The drop in the hardness of HAZ on the printed side is less compared to the wrought-aged side. The combination of thermal cycling effects and strain-induced dislocations results in a higher hardness profile seen in the HAZ of the printed side (HAZ-P) compared to the HAZ of the wrought side (HAZ-W). This study confirms that welding additively manufactured Haynes 282 with wrought Haynes 282 is a workable option for joining additively manufactured heat exchanger components of complex geometry.

To identify the best conditions for hot deformation, it is necessary to design innovative alloy systems. Data on flow stress and strain under various hot working scenarios are critical for creating processing (Hot Workability) maps. The deformation characteristics of Ti71Fe25.15Sn3.85 ternary alloys were explored through hightemperature compression experiments by a Gleeble (R) simulator at different temperature (700 degrees C, 800 degrees C, 900 degrees C, and 950 degrees C) with strain rates of 0.01 s- 1, 0.1 s- 1, and 10 s- 1. The alloy exhibited a fine eutectic structure composed of beta-Ti and FeTi phases, alongside coarse dendritic Ti3Sn and FeTi phases. Five machine learning (ML) models were employed for predicting the flow curve for another strain rate 1 s-1 and generating processing maps. The random forest (RF) model shows exceptional accuracy an R2 (coefficient of determination) of 96.7 %, RMSE (root mean square error) of 9.6 %, and MAE (mean absolute error) of 6.4 %.

Optimizing hot deformation conditions is critical for achieving efficient thermo-mechanical processing of advanced alloy systems. In this study, a multicomponent Ni48Cu10Co2Ti38Ta2 alloy was developed, exhibiting a refined eutectic microstructure composed of NiTi and Ni3Ti phases, along with coarse Ti2Ni and NiTi dendritic phases. High-temperature compression tests were performed using a Gleeble (R) thermo-mechanical simulator over a temperature range of 973-1273 K and strain rates from 10-2 to 10 s-1 to investigate the alloy flow behavior. To reduce experimental efforts and enhance prediction accuracy, five machine learning (ML) models random Forest (RF), XGBoost (XGB), decision tree (DT), K-Nearest neighbor (KNN), and gradient boosting (GB) were applied to predict the flow stress-strain response and construct processing maps. Among these, the RF model demonstrated superior predictive performance, particularly at a strain rate of 0.1 s-1, with R2 = 0.97, RMSE = 10.1 %, and MAE = 8.9 %. The flow curves predicted by the RF model were used to develop precise processing maps, identifying optimal and safe deformation conditions. The resulting processing maps were validated through experiments, confirming that the alloy can be safely deformed within the temperature range of 1173-1273 K and strain rates between 10-0.8 and 10-2 s-1. This integrated experimental-computational approach offers a reliable and efficient strategy for determining hot working conditions, reducing material and energy consumption. It also presents a robust framework for advancing the development of high-temperature alloy systems through the combination of ML techniques and experimental validation.

Higher capacity materials, such as Si and Sn are known to have phase separating behavior during the (de)lithiation. While initial models for lithiation in graphite electrode were based on single phase diffusion, with the introduction of Si and Sn, disposition of the models has shifted to the two-phase diffusion. It is important to understand the interaction of various phenomenon in materials which show phase change during (dis)charging cycles. In this work, we present a phase field model to simulate two-phase lithiation. This model is used to study the electrochemical response of the system by conducting numerical voltammetry. The main goal of this effort is to highlight the difference in electrochemical response occurring during single-phase diffusion and two-phase diffusion and explain the ensuing physics. Furthermore, effect of elasticity which governs the phase-change process and also alters corresponding voltammograms is also studied in detail. The voltammograms show clear shift in current peaks' size and position for the changing diffusion behavior. Also as elasticity affects the two-phase diffusion, change in nucleation timing and diffusion rate are visible in voltammograms. Additionally, it is also observed how elasticity can cease the phase separation behavior and voltammogram for two-phase diffusion can become identical to single-phase diffusion.

The addition of Zn to AlCrFeCoNi high-entropy alloy (HEA) poses intriguing questions as to how it would affect phase evolution. Herein, the phase evolution in AlCrFeCoNiZn is studied using a combination of experimental techniques (X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, and differential scanning calorimetry) and computational (density-functional theory [DFT], calculation of phase diagrams, and machine-learning) methods. Mechanically alloyed and spark-plasma-sintered AlCrFeCoNiZn assumes a metastable single-phase, body-centered-cubic (BCC) structure that undergoes diffusion-controlled phase separation upon subsequent heat treatment to form separate (Al, Cr)-rich, (Fe, Co)-rich, and (Zn, Ni)-rich phases. The formation of (Al, Cr)-rich phase, not reported previously in AlCrFeCoNi-based HEAs, is attributed to strong clustering tendency of Cr-Zn and Cr-Ni pairs, combined with the strong ordering of Zn-Ni pair, driving out Cr that in turn combines with Al to form a (Al, Cr)-rich phase. In the DFT results, the formation of thermodynamically stable L12 phase is shown wherein Cr-Fe-Zn [Al-Ni-Co] preferably occupy1a (000) [3c (0 1/2 1/2)] positions. The sluggish diffusional transformation to L12 phase from BCC precursors is attributed to the small stacking-fault energy of AlCrFeCoNiZn. The equilibrated HEA exhibits a high microhardness of 8.24 GPa with an elastic modulus of 184 GPa. In this work, the addition of Zn to AlCrFeCoNi high-entropy alloy is probed. The formation of an (Al, Cr)-rich phase is observed, owing to the large ordering tendency of the Al-Ni pair that results in the formation of (Al, Ni)-rich phases. The Zn addition drives new ordering and clustering behavior, which results in phase separation.image (c) 2024 WILEY-VCH GmbH

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-controlled phase selection observed at high solidification velocities relevant to additive manufacturing. The implemented model predicted the growth controlled phase selection in multicomponent alloys, which the other models with linear phase diagram could not. These models are calculated for different steels and the results are compared with experimental observations.

The increasing demand for higher energy capacity in lithium-ion batteries has underscored the significance of modeling lithiation with alternative electrode materials, such as silicon (Si) and tin (Sn). This research addresses the need for comprehensive insights into the (dis)charging process, particularly focusing on the intricate phase transformations in the anode. Phase-field modeling has proven effective in capturing these transformations [2], revealing volumetric deformations of up to 300% during (dis)charging cycles [1]. Unfortunately, these deformations compromise material integrity, leading to reduced battery cycle life and reliability. To address these challenges, our work presents a novel framework for modeling lithiation in materials exhibiting two-phase diffusion using phase field modeling. Unlike previous models limited to single-phase diffusion, our framework provides a more realistic representation of the diffusion process. This realism is achieved by incorporating the time-dependent voltage applied to the anode, a crucial factor in understanding the electrochemical response during lithiation [3]. Furthermore, we leverage the currents generated during the lithiation and delithiation processes to conduct a comprehensive voltammetric study. This study goes beyond existing research by considering the impact of phase separation on the currents developed during Li-ion battery operation. Our findings aim to contribute valuable insights into optimizing battery performance and addressing challenges associated with phase transformations, ultimately advancing the development of high-capacity anodes for lithium-ion batteries. REFERENCES [1] McDowell M. T., Lee S. W., Nix W. D., Cui Y. 25th Anniversary Article: Understanding the Lithiation of Silicon and Other Alloying Anodes for Lithium-Ion Batteries . Adv. Mater., Vol. 25 (36), pp. 4966–4985, 2013. [2] Chen L., Fan F., Hong L., Chen J., Ji Y. Z., Zhang S. L., Zhu T., Chen L. Q. A Phase-Field Model Coupled with Large Elasto-Plastic Deformation: Application to Lithiated Silicon Electrodes . J. Electrochem. Soc. , Vol. 161 (11), pp. F3164–F3172, 2014. [3] Swaminathan, N., Balakrishnan, S., & George, K. Elasticity and Size Effects on the Electrochemical Response of a Graphite, Li-Ion Battery Electrode Particle . Journal of The Electrochemical Society , 163 (3), A488–A498, 2016. Figure 1

During the laser powder bed fusion(L-PBF) process, the rapid solidification conditions coupled with repeated heating and cooling cycles constrain the design potential and printability of complex-shaped structures, especially for part-scale components. Process-induced residual stress, porosity, and crystallographic texture are the most challenging obstacles when designing quality components using this process. These defects also have a detrimental impact on the quality and structural durability of the deposited parts. To comprehend the coupled effect of these determinants on the mechanical performance of various orientated components, we perform a sequentially coupled thermo-mechanical simulation to obtain the residual stress evolution during the deposition as well as on printed coupons after the extraction of the support structure. Simulated outcomes have been verified using X-ray diffraction, and there is a good convergence between simulated and experimental values with a 10% maximum difference. X-ray tomography and Electron back scattered diffraction(EBSD) techniques were utilized to quantify the process-induced porosity(distribution and size) and crystallographic texture in the solidified component, respectively. The mechanical performance of the deposited components was evaluated using uniaxial tensile tests. The cracking behavior in fractured samples was studied using SEM-based fractography. Due to more number of repeated thermal cycles, the vertically deposited sample had higher residual stress, larger grains, and thus lower strength.

Haynes 282 is a weldable, γ′ strengthened Ni-based superalloy and is a suitable candidate for aerospace and power-generation applications. Laser powder bed fusion (LPBF) of Haynes 282 is gaining attention recently due to its superior mechanical properties than its conventional counterparts. In spite of the superior mechanical properties, there are significant challenges concerning crystallographic anisotropy. One of the critical but less studied parameters that influence crystallographic anisotropy is the laser scan rotation angle. This study investigates the effect of laser scan rotation angle on the microstructure and subsequently on the mechanical properties. The samples fabricated with 90° scan rotation exhibited stronger texture while the samples with 137° rotation had weaker texture than samples with 67°. Further, three-dimensional Finite difference-Monte Carlo simulations were performed to understand the microstructure evolution with varying process parameters. The experimental and simulated microstructures are quantitatively compared using 2-point correlations. The texture and grain morphology evolution are explained based on melt pool morphology and microstructure simulations. Mechanical properties of as-built and aged samples are estimated using theoretical models and agree well with the experimental results.

This study explores the potential of cold spray technology for repairing high-strength Al7075 alloy components, particularly in the aerospace industry. The gas-atomized powder contains a dendritic cell structure with solutes segregated at the dendritic cell boundaries. Thus, direct aging of atomized powder fails to induce the formation of strengthened precipitates. Therefore, the effect of different powder pre-treatments on the deposition efficiency, microstructure, and aging behavior of the coatings was investigated. Cold spray coatings were deposited using as-received powder, solutionized, and solutionized + aged powders, revealing a significant improvement in thickness for coatings obtained using solutionized (110