Effect of Melt Superheating Treatment on Directional Solidification Interface Morphology of Multi-component Alloy

The influence of melt superheating treatment on the solid/liquid （S/L） interface morphology of directionally solidified Ni-based superalloy DZ125 is investigated to elucidate the relationship between melt characteristic and S/L interface stability. The results indicate that the interface morphology is not only related to the withdrawal velocity （R） but also to the melt superheating temperature （Ts） when the thermal gradient of solidification interface remains constant for different Ts with appropriate superheating treatment regulation. The interface morphology changes from cell to plane at R of 1.1 μm/s when Ts increases from 1500°C to 1650°C, and maintains plane with further elevated Ts of 1750°C. However, the interface morphology changes from coarse dendrite to cell and then to cellular dendrite at R of 2.25 μm/s when Ts increases from 1500°C to 1650°C and then to 1750°C. It is proved that the solidification onset temperature and the solidification interval undergo the nonlinear variation when Ts increases from 1500°C to 1680°C, and the turning point is 1650°C at which the solidification onset temperature and the solidification interval are all minimum. This indicates that the melt superheating treatment enhances the solidification interface stability and has important effect on the solidification characteristics.

Current development in quantitative phase-field modeling of solidification

The quantitative phase-field simulations were reviewed on the processes of solidification of pure metals and alloys.The quantitative phase-field equations were treated in a diffuse thin-interface limit,which enabled the quantitative links between interface dynamics and model parameters in the quasi-equilibrium simulations.As a result,the quantitative modeling is more effective in dealing with microstructural pattern formation in the large scale simulations without any spurious kinetic effects.The development of the quantitative phase-field models in modeling the formation of microstructures such as dendritic structures,eutectic lamellas,seaweed morphologies,and grain boundaries in different solidified conditions was also reviewed with the purpose of guiding to find the new prospect of applications in the quantitative phase-field simulations.

Investigation on Reaction Interface between the Aluminum and K2ZrF6 by Freezing the Molten Salt Reaction

A reaction interface between the aluminum and K_2ZrF_6 during molten salt reaction process was frozen by quenching the mold in water, and the interface structure was analyzed to determine the formation process of Al_3Zr. Results show that a clear conical interface existed between the K_2ZrF_6 and aluminum. A zirconium accumulation layer with the thickness of about 2–3 lm was formed at the aluminum side of the interface. Many initially formed Al_3Zr particles（with the size of 0.4–16 lm） distributed in this layer, most of which located at the interface. The morphology of Al_3Zr particles is closely related with their size. For the size of 0.4–1 lm, the Al_3Zr appeared as globular and ellipsoid shapes. When it grew to the size of 1–2 and 2–16 lm, it exhibited the rule cube shape, and rule cuboids shape, respectively.

Analysis of microcrystal formation in DS-silicon ingot

The DS(directional solidification) polycrystalline silicon ingot is the most important photovoltaic material today,and the conversion efficiency of solar cells is affected by the morphology and organization of the crystal.Uniform grains with larger size are conducive to get high-quality wafer,so improving the cell conversion efficiency.However,grains sizes that are less than 1 mm2 can be observed frequently in the central district of mc-Si ingots,which bring negative effect to the quality of the mc-Si ingot and decrease the electrical performance of wafer.In this paper,we make an attempt to explain the formation mechanism and influence factors of microcrystal in mc-Si ingot with computer simulation technology and theory of component supercooling.It was found that:to avoid production of microcrystal,it's better to increase the value of G/V(V is the growth rate and G is the near-interface temperature gradient),strengthen the melt convection front in the solidification interface and keep a fairly flat solid/melt interface in producing mc-Si ingot.

Microstructure Formation in Al-Bi-Co Immiscible Alloys Directionally Solidified with Different Melt Superheat Temperatures

The directional solidification has been carried out for the AI-413i-2,5Co （wt pct） alloys with different melt superheat temperatures. The microstructure characterization and the quantitative metallographic analysis have been performed. The results indicated that the Bi-rich sphere size and cellular spacing decrease with increasing melt superheat temperature. The interaction between the advancing solidification interface and the Bi-rich spheres with different sizes was analyzed. The effect of the melt superheat treatment on microstructure evolution was discussed for the immiscible alloys. The microstructure development in ternary Al-Bi-Co alloys directionally solidified with different melt superheat temperatures was clarified.