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Abstract: Bulk samples of Fe–25 at.% Ge peritectic alloy are undercooled up to 260 K using electromagnetic levitation technique. The growth rate of the primary phase is measured using a capacitance proximity sensor technique. Solidification microstructure is studied as a function of undercooling. The microstructure of samples at low undercoolings consists of a residual primary phase α2, peritectic phase ε and inter-dendritic ε–β eutectic. Microstructure at higher undercoolings is nearly phase-pure ε. Time resolved diffraction analysis of the levitated droplets using synchrotron radiation indicates the nucleation of primary α2 in all cases. The growth rate is analysed using current theories to explain the experimental observations. Interfacial undercooling is found to play an important role in the growth kinetics. Our results also suggest suppression of peritectic reaction. [Copyright &y& Elsevier]

[Display omitted] • Bundling 20 physical layers in a single voxel reduces computational complexity. • Residual stress evolution during deposition and postprocessing was studied in depth. • Temperature gradient and eigen strain are significant to residual stress evolution. • Effect of layer thickness variation on residual stress evolution was studied. • The experimental flow curve was very effective for thermo-mechanical simulation. Laser Additive Manufacturing (LAM) is a promising technology for manufacturing gas turbine components with enhanced design capability and a significant reduction in part weight. Additive manufacturing of alloy 718 using Laser Powder Bed fusion (L-PBF) process poses certain challenges pertaining to complex residual stress, micro-segregation of Nb, and undesired Laves phase formation in the as-printed state. The built-up residual stress and undesired brittle phase may lead to cracks and build failures. This article studied residual stress evolution during L-PBF of alloy 718 using Finite Element (FE) thermo-mechanical simulation implemented in Simufact Additive® software. The model adopted the bundling of physical powder in voxel mesh to minimize the computational time and mimic the actual process scenario during part-scale simulation. Experimental flow curves generated from Gleeble 3800® tests at elevated temperatures were utilized to calibrate material property for better accuracy in the FE simulation. The calibrated model was used to study the residual stress evolution during support structure removal. Verification and validation of simulated results were performed using X-ray diffraction (XRD) measurements. The simulated value agrees well with the experimental value with a maximum deviation of 7%. Finally, the experimentally validated model was used to correlate the effect of layer thickness variation on residual stress evolution. [ABSTRACT FROM AUTHOR]

Establishing growth kinetics of undercooled metallic alloys is essential to understand microstructure evolution during solidification processing. The complexity of the physical processes have hitherto limited growth models to simple assumptions that do not lead to satisfactory predictive capability. Experimental measurements of growth velocity as a function of undercooling are also tedious. The current study uses experimental and literature data to train the machine learning algorithms. Five algorithms are trained: Random Forest, Bagging Regressor, Gradient Boosting Regressor, XGBoost, and Artificial Neural Network. A labeled data set of 910 was used, with 70% data for training and 30 % data for testing. An R2 cross-validation score of more than 0.89 was obtained for ANN. The trained algorithms are used to predict the growth velocity of medium and high entropy alloys show good compatibility with the experimental data. [Display omitted] [ABSTRACT FROM AUTHOR]

The non-equilibrium response of a high entropy alloy CoCuFeNiTa 0.5 has been studied using undercooling as a control parameter. The solidification growth rates are rapid (30–50 m/s) at deep undercooling (>150 °C) and are comparable with conventional alloys. The elemental segregation especially that of Cu as predicted by phase field simulations in lower (<50 °C) undercooling regime matches with the experimental observations. This study indicates that even extreme non-equilibrium conditions during solidification could not avoid elemental segregation at the atomic scale. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Identifying optimum processing conditions is necessary for new material development. The flow curves can be used to develop the processing map for an alloy. The current study trained multiple machine learning models such as Random Forest Regressor (RFR), K Nearest Neighbors (KNN), Extra Tree Regressor (ETR) and Artificial Neural Network (ANN) to predict the flow behaviour of the material. The testing R2 fit score of more than 0.99 was obtained for all four algorithms, and trained models were used to generate the flow curves at various temperature strain rate combinations for CoCrFeNiTa 0.395 eutectic high entropy alloy. A processing map was developed using the results from ANN and validated with the experimental microstructure observations. [Display omitted] [ABSTRACT FROM AUTHOR]

Multicomponent Co 20 Cu 20 Fe 20 Ni 20 Ti 20 eutectic high entropy alloy (HEA), processed by vacuum arc melting cum suction casting technique was studied. The microstructure of this eutectic HEA consists bcc (β) and fcc (α 2 ) solid solution dendritic phases and eutectics (fcc (α 1 ) plus Ti 2 (Ni, Co)-type Laves phase). Serrations in the flow behaviour are attributed to multi substitutional solutes in the multi-phase microstructure. Based on the detailed analysis of mechanical data together with deformed microstructural characterization, the optimum thermo-mechanical processing conditions for hot working are identified as T=930–990 °C (1203–1263 K) and strain rate range of 10 −3 s −1 –10 −1 s −1 . [ABSTRACT FROM AUTHOR]

• Design and development of Co 25 Cr 20 Fe 25 Ni 25 V 5 FCC high entropy alloy (HEA) using ICME approach. • Understanding the segregation behavior of FCC HEA using phase field simulation. • Formation of the deformation bands in the lower temperature range 1073–1173 K causes hardening. • Observation of annealing twin in FCC HEA during deformation in the high temperature range 1273–1373 K. [Display omitted] In the present study, using ICME approach, the development of Co-Cr-Fe-Ni-V based single-phase FCC high entropy alloy (HEA) has been explored. The simulation guided composition was arc melted and verified using microstructure characterization. The as-cast sample was subjected to deformation at a strain rate of 0.1 s−1in the temperature range of 1073–1373 K. The flow stress behavior in this temperature range could be correlated with the evolution of microstructure using EBSD. Based on these results, the deformation behavior of the alloy at elevated temperature is rationalized. The current study realizes the ICME approach to develop novel single-phase FCC HEA. [ABSTRACT FROM AUTHOR]