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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: 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]

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]