Search

A commercial grade Nd15.5Fe78B5Cu1.5 alloy was prepared through the melting-casting route. The as-cast (AC) alloy was characterized by X-ray diffraction (XRD) and scanning electron microscopy techniques. XRD and energy-dispersive spectroscopy analyses revealed the presence of Nd2Fe14B, Nd2Fe17, Nd-rich phase (Nd/NdCu eutectic), and α-Fe phases in the AC specimen. Retainment of α-Fe in the AC microstructure makes a core-shell type microstructure in this condition. Thermodynamic predictions based on the non-equilibrium (Scheil-Gulliver) solidification calculations validate the retainment of both α-Fe and Nd2Fe17 phases in the AC microstructure. A homogenization treatment has been conducted at 1373 K for 2 h, which effectively results in a substantial reduction in the phase fraction of remnant α-Fe. [ABSTRACT FROM AUTHOR]

Continuous casting of high-strength steels is challenging owing to peritectic phase transformation during solidification. This transformation is reported to be either diffusion controlled or "massive" like. The experimental evidence suggests that constant thermal gradients lead to diffusion-controlled phenomena, whereas the concentric solidification technique induces massive transformation. Diffusion-controlled peritectic solidification is more desirable during continuous casting to ensure a suitable cast quality compared with massive transformation. Accordingly, the authors demonstrate a general one-dimensional numerical modeling of the solidification process in steel by incorporating a diffusion-controlled peritectic phase transformation. The model is dynamically linked with the FactSage thermodynamic database through ChemAppV 7.1.4 library for input of accurate thermodynamic data. The modeling details are presented for a binary Fe-C system, and the results are compared with the experimental data available in the literature. The growth and dissolution of phases are accurately predicted as a function of composition and cooling rate. [ABSTRACT FROM AUTHOR]

A one-dimensional numerical solidification model has been developed to predict the recovery and refining efficiency of fractional crystallization applied to a blend of aircraft Al scraps with variations of Fe and Si. The model incorporates the effective partition coefficient depending on the degree of melt stirring. Moreover, the kinetic factors that affect the formation of primary Al FCC during fractional crystallization such as solidification velocity, thermal gradient, cooling rate, and solute back-diffusion are taken into account. The simulation results suggest that the optimum solidification velocities that are able to yield the highest refining can be ranged between 1.0 × 10 and 1.0 × 10 m/s with medium to high stirring levels. The maximum recovery of refined Al has been estimated to be 31 wt pct of the initial scrap when the process is carried out at 1 × 10 m/s and the initial concentrations of Fe and Si are 1 and 2 pct, respectively. [ABSTRACT FROM AUTHOR]

The present lays emphasis on the effect of varying degrees of undercooling on the microstructure development of the Fe50Cu50 alloy system. A sufficiently high undercooling (>100 °C) was achieved using the aerodynamic levitation (ADL) technique whereas a W-wire holding method in the same ADL setups was employed to attain relatively low undercooling (87 °C) during solidification. In addition, solidification experiments were also performed without any undercooling in this alloy system. Thus, the effect of a wide range of undercooling on the phase separation and microstructural development of the Fe-Cu system was systematically investigated in this work. In a substantially undercooled ADL sample, a complete phase-separated micrograph was obtained, but in other situations, a discontinuous network of Cu in interconnected Fe dendritic areas was detected as determined by the scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). X-ray diffraction (XRD) of the sample cross-section confirms that the phases present at the end of the solidification process are α-Fe and Cu, regardless of the degree of undercooling. In the instance of the ADL sample, the entrapment of Cu droplets in the inter-connected Fe dendritic area due to a combination of high undercooling and centrifugal force was detected using X-ray tomography, and the orientation distribution of the samples was determined using Electron Backscatter Diffraction (EBSD). [Display omitted] • Effect of undercooling on the phase separation of Fe50Cu50 Immiscible alloy has been studied. • For sample preparation, the Aerodynamic Levitation Technique (ADL) and a novel technique called the W-wire method are used. • The phase separation of the solidified sample is visualized using four-dimensional X-ray tomography. • The EBSD and SEM-EDS confirm that phase separation occurs due to liquid droplet coalescence at higher undercooling. • The dominant effect of Marangoni force and Stokes force causes complete phase separation in case of sample prepared by ADL. [ABSTRACT FROM AUTHOR]

A systematic experimental investigation on microsegregation and second phase fraction of Mg-Al binary alloys (3, 6, and 9 wt pct Al) has been carried out over a wide range of cooling rates (0.05 to 700 K/s) by employing various casting techniques. In order to explain the experimental results, a solidification model that takes into account dendrite tip undercooling, eutectic undercooling, solute back diffusion, and secondary dendrite arm coarsening was also developed in dynamic linkage with an accurate thermodynamic database. From the experimental data and solidification model, it was found that the second phase fraction in the solidified microstructure is not determined only by cooling rate but varied independently with thermal gradient and solidification velocity. Lastly, the second phase fraction maps for Mg-Al alloys were calculated from the solidification model. [ABSTRACT FROM AUTHOR]

A numerical formulation of solidification model which can predict the microsegregation and microstructural features for multicomponent alloys is presented. The model incorporates the kinetic features during solidification such as solute back diffusion, dendrite tip undercooling, and secondary arm coarsening. The model is dynamically linked to thermodynamic library for accurate input of thermodynamic data. The modeling results are tested against the directional solidification experiments for Mg-Al-Zn alloys. The experiments were conducted in the cooling rate range of 0.13 to 2.33 K/s and microstructural features such as secondary arm spacing, primary dendrite arm spacing, second phase fraction, and microsegregation were compared with the modeling results. Based on the model and the experimental data, a solidification map was built in order to provide guidelines for as-cast microstructural features of Mg-Al-Zn alloys in a wide range of solidification conditions. [ABSTRACT FROM AUTHOR]

Abstract: A comprehensive microstructural evolution of Mg–1.5, 4.0 and 5.5wt% Zn alloys with respect to the solidification parameters such as thermal gradient (G), solidification velocity (V), cooling rate (GV) and solute (Zn) content were investigated in the present study. Solidification techniques such as directional solidification and wedge casting were employed in order to obtain cooling rates between 0.05 and 250K/s. Microstructural features such as secondary dendrite arm spacing (SDAS), primary dendrite arm spacing (PDAS), microsegregration along the secondary dendrites and secondary phase fractions were experimentally determined. A solidification model that incorporates solute back diffusion, secondary arm coarsening, dendrite tip undercooling and dynamically linked with accurate thermodynamic databases is used to explain the experimental results. [Copyright &y& Elsevier]

Abstract: The comprehensive microstructural evolution of Mg–3, 6 and 9wt.% Al alloys with respect to the solidification parameters such as thermal gradient (G), solidification velocity (V), cooling rate (G·V) and solute (Al) content were investigated in the present study. Various solidification techniques, including directional solidification, wedge casting, sand and graphite mould casting, gravity casting in a Cu mould and water quenching, were employed in order to obtain wide ranges of cooling rates between 0.05 and 1000Ks–1. The microstructural length scales of Mg–Al alloys, such as secondary dendrite arm spacing and primary dendrite arm spacing, were determined experimentally and compared with published models. In addition, the solidification parameters of morphological transitions such as cellular to columnar dendrite and columnar to equiaxed dendrite were also determined. Based on all the experimental data and the solidification model, a solidification map was built in order to provide guidelines for the as-cast microstructural features of Mg–Al alloys. [Copyright &y& Elsevier]

• Tri-phasic alloy nanoparticles (NPs) embedded in IQC matrix were synthesized by rapid solidification route. • Particles typically less than 50nm contribute to the formation of (γ-Sn) whereas larger particles exhibit (β-Sn) within the nanoparticle. • In DSC, no distinct exothermic peak was observed on cooling, indicating solidification occurring over a ranges of temperature. • Solidification sequence of NPs are: (Bi) (0 °C) → (β-Sn)/(γ-Sn) (−60 °C) → BiIn (−100 °C). • Detailed thermodynamic modeling of the Bi-In-Sn system with different nano-sizes were evaluated. [Display omitted] The present manuscript aims to understand the solidification and alloying behavior of the nanoscaled multiphase Bi-In-Sn nanoparticles embedded in the icosahedral quasicrystalline (IQC) matrix, synthesized using the melt spinning route. Detailed transmission electron microscopy (TEM) investigation reveals the formation of three distinct phases; tetragonal BiIn, rhombohedral (Bi), hexagonal (γ-Sn) or tetragonal (β-Sn) within the nanoparticles depending on the size. It also shows that BiIn and (Bi) exhibit a reasonably good lattice match with the IQC matrix, whereas (γ-Sn) does not obtain any orientation relationship with surrounding IQC. The DSC investigations show a sharp melting peak, whereas no distinct exothermic peak was observed on cooling, indicating solidification occurring over a range of temperatures. To investigate the extent of undercooling required for solidification, careful cyclic heating, and cooling experiments were performed in the DSC. The results suggest that the nanoparticles can completely be solidified by cooling to −160 °C, indicating extensive undercooling required for solidification. In-situ XRD during cooling depicts that the solidification is triggered by the nucleation of the primary (Bi) phase at 0 °C. Careful thermodynamic modeling of the Bi-In-Sn system with different nano-sizes were evaluated to interpret the size-dependent solidification behavior of the nanoalloy particles. The experimental results can be compared with the calculated nanophase diagram, presenting a reasonably good match. [ABSTRACT FROM AUTHOR]

Titanium based alloys are one of the important structural materials with applications ranging from aerospace to biomedical industries. Several ternary Ti–Si–Sn alloys were explored in this study to design the microstructure comprising of binary and ternary eutectics corresponding to Ti–Si, Ti–Sn and Ti–Si–Sn system. The microstructural evolution in these alloys was studied using a combination of characterization techniques and thermodynamic calculations. The predicted solidification path from thermodynamic calculations well supported the experimental microstructural data. In addition, mechanical property and microstructure relationship were determined by performing hardness measurements and evaluating stress-strain curves under compression. [ABSTRACT FROM AUTHOR]