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Highlights: [•] Grain size of AZ91 alloy reduced from 500μm to 124μm by SiC inoculants. [•] Solution route is 400°C+16h for spheroidization without notable grain growth. [•] Pressurized solidification favors the flow and feeding capacity of residual liquid. [•] Relative density increases continuously with the increase of holding pressure. [•] Tensile strength reaches 167MPa for modified alloy with applied pressure. [ABSTRACT FROM AUTHOR]

Abstract: The dependence of microstructure on undercooling for Cu50Co50 immiscible alloy and the relations between dendrite fragmentation and liquid phase separation were studied by melt-fluxing in combination with cyclic superheating. It is shown that homogeneous dispersed structure can be obtained by dendrite fragmentation because of the increased solute content in primary dendrite, which is advantageous for strengthening dendrite remelting effect and thermal plateau time following recalescence. As for the sample after liquid separation, typical dual-layer structure forms, while dendrite fragmentation still exists and its extent, volume fraction are influenced by the solute contents of two immiscible layers. Quantitative thermodynamic calculation was further performed to support the experimental results. [Copyright &y& Elsevier]

Abstract: Considering nucleation, growth and impingement, a numerical model was proposed to describe the transformation kinetics of rapid solidification in bulk undercooled Fe–B hypereutectic alloy. Applying heat balance and solute conservation, the changes of temperature and composition of residual liquid are proved to be not only dependent of time, but also associated with the solidified fraction during the transformation. Accordingly, the driving force for non-equilibrium solidification, as well as the determined nucleation and growth rates, decreases with the process of transformation. On this basis, the primary grain size distribution formed in this process can be predicted with the combination of classical Kolmogorov–Johnson–Mehl–Avrami (KJMA) equation and a probability statistic analysis. Good agreement between the model prediction and experimental results has shown the validity of the proposed model. [ABSTRACT FROM AUTHOR]

Abstract: Assuming phenomenological thermal flow balance and solute conservation, the non-equilibrium transformation path has been studied for recalescence of bulk undercooled hypereutectic Fe–B alloy. Taking advantage of the defined stoichiometry for primarily formed intermetallic Fe2B, a convenient and accurate tracking of the average liquid concentration during recalescence can be performed. Applying thermodynamic calculations for liquid/solid Gibbs energy difference, the predictions of the post-recalescence temperature T R and the as-formed solid fraction in recalescence are shown to be in good agreement with the experimental results. On this basis, a transformation path accompanied by the evolution of temperature and concentration in the residual liquid has been constructed. This clearly shows a transition from non-equilibrium to near-equilibrium process upon recalescence. [Copyright &y& Elsevier]

Abstract: In the present work, thermodynamic and kinetic calculations were combined to study the glass forming ability of Cu–Zr binary system. Applying thermodynamic association model, the primarily crystallized phase and its corresponding driving force can be determined firstly. Then, the whole Time–Temperature–Transformation (TTT) diagrams basing on homogeneous and heterogeneous nucleation modes have been constructed quantitatively. As for the former case, the critical cooling rate is underestimated by about three orders of magnitude in comparison with the experimental observation. As for the latter case adopting suitable values of catalytic factor f(θ) and potential nuclei N 1, the predictions agree well with the experimental results, and moreover, the nose temperature of TTT diagram is upper-shifted. This has been discussed using a competition of the atomic mobility and the reduced nucleation barrier, as well as its further effect on the nucleation and growth process. [Copyright &y& Elsevier]

Highlights: [•] Microstructure of AZ91D alloy can be refined apparently by rare element Ce. [•] Pressurized solidification favors the flow and feeding capacity of residual liquid. [•] Micro-segregation and eutectic phase are reduced by strengthened flow behavior. [•] Shrinkage void is suppressed by the enhanced feeding capacity. [•] Both grain refinement and denser structure improve the tensile strength. [Copyright &y& Elsevier]

Abstract: Applying melt-fluxing, how to predict the maximal recalescence temperature T R upon rapid solidification of bulk undercooled Cu70Ni30 alloy has been investigated. Reproducible experimental results show that T R decreases with the increase of the initial melting undercooling ΔT, and moreover, its value is much lower than that predicted by Level rule and Scheil equation, let alone the equilibrium liquidus temperature. Quantitative thermodynamic calculation, in combination with an analysis of solute distribution, demonstrates that, T R is affected by the difference of Gibbs free energy between the residual liquid and solid after recalescence. Subjected to sufficiently high ΔT, T R should be nearly equal to the thermodynamic T 0 point corresponding to the concentration of the residual melt after recalescence. [Copyright &y& Elsevier]

Abstract: The effects of convection diffusion, gravity, temperature gradient on the liquid-phase separation were discussed in this work. Originally, collision and congregation were mainly controlled by Brown motion of droplets, which was strong influenced by the initial density of droplets in undercooled melt. As the droplets radius increased, the velocities of Stokes and Marangoni motion increased continuously. Compared to Marangoni migration, Stokes motion was easier influenced by the number and radius of droplets. Moreover, Stokes motion plays a dominant role in the collision and congregation process when a critical radius rd was far exceeded. [Copyright &y& Elsevier]

Abstract: Assume that the intergranular phase (IP) existing between adjacent grains is a weak magnetic phase, and could weaken or interrupt the intergrain exchange-coupling interaction (IECI). Using our proposed cubic-grain anisotropy model, we investigate the effects of IP''s thickness d, and its anisotropy constant K 1(0) on the coercivity of nanocrystalline Nd–Fe–B magnet. Calculation results indicate that the coercivity increases with increasing d, but decreases with increasing K 1(0). When d =1.2nm and K 1(0)=0.5K 1 (K 1 is the common anisotropy constant of the bulk Nd–Fe–B material), our calculated results are consistent with available experimental data. [Copyright &y& Elsevier]

Abstract: The effect of microstructure on the anisotropy and the coercivity in HDDR Nd–Fe–B magnet has been investigated by putting forward a theoretical anisotropy model influenced simultaneously by both the structure defect and the exchange coupling interaction. The results showed that the coercivity is greatly influenced by both the defect thickness, r 0, and the anisotropy constant, K 1(0), at grain surface. Coercivity is determined by the pinning mechanism when K 1(0)≤0.4K 1 and r 0 <4nm or K 1(0)>0.4K 1. However, it is controlled by the nucleation mechanism when K 1(0)≤0.4K 1 and r 0 >8nm. For all values of K 1(0), the coercivity first increases, reaches the maximum and then decreases with increasing r 0, and its maximum value decreases with increasing K 1(0). The maximum coercivity is 1102KA/m while K 1(0)=0 and r 0 is close to the thickness of domain wall (∼4nm), which is consistent with experimental results given by other authors. [Copyright &y& Elsevier]

Abstract: Sm(Co0.68Cu0.07Fe0.22Zr0.03)7.5 nanocrystalline melt-spun ribbons are prepared at different speeds. The results show that the ribbons consist of Sm(Co,M)7(M=Cu, Fe, Zr) main phase and a little α-Fe phase. And the ribbons are composed of three areas: equiaxed area, columnar area, and dendritic crystal area. Preferred orientation exists in both the columnar area and the dendritic crystal area. Following the increase of the melt-spun speed, the orientation degree of melt-spun ribbons increases first, then descends, and reaches the maximum ratio I (002)/I (111) of 3.81 when the speed is 20m/s. Preferred orientation in the ribbons helps to improve the magnetic properties of ribbons. The best comprehensive magnetic properties of the ribbons melt-spun at 20m/s are M r =39.27emu/g, M s =75.79emu/g, H ci =1301.9Oe, and M r/M s =0.52. [Copyright &y& Elsevier]