We report the results of a phase-field study of degenerate seaweed to tilted dendrite transition and their growth dynamics during directional solidification of a binary alloy. Morphological selection maps in the planes of (G, V_p) and (ε₄, V_p) show that lower pulling velocity, weaker anisotropic strength and higher thermal gradient can enhance the formation of the degenerate seaweed. The tip undercooling shows oscillations in seaweed growth, but it keeps at a constant value in dendritic growth. The M-S instability on the tips and the surface tension anisotropy of the solid-liquid interface are responsible for the formation of the degenerate seaweed. It is evidenced that the place where the interfacial instability occurs determines the morphological transition. The transient transition from degenerate seaweed to tilted dendrite shows that dendrites are dynamically preferred over seaweed. For the tilted dendritic arrays with a large tilted angle, primary spacing is investigated by comparing predicted results with the classical scaling power law, and the growth direction is found to be less sensitive to the pulling velocity and the primary spacing. Furthermore, the effect of the initial interface wavelength on the morphological transition is investigated to perform the history dependence of morphological selection.

Lithium batteries have been widely used, but the growth of lithium dendrites does lead to some hazards, such as internal short circuit, thermal runaway and even explosion. In paper, a nonlinear phase field model combined with Butler-Volmer expression was developed to study dendrite growth during electrodeposition. Two types of initial electrode-electrolyte interface are applied in numerical simulations. Results show that the cation concentration enrichment occurs near the dendritic tip due to the electromigration, and the curve of the growth velocity versus time follows a simple power law relation, indicating that the stability of the dendritic array originating from initial electrode-electrolyte interface can be broken with the applied electrical potential increasing. Moreover, we found that applied electric potential gradient can strongly influence the dendritic growth velocity and the dendritic growth during electrodeposition is less relative to the surface tension anisotropy.

Experiments on transient directional solidification were carried out to study the columnar to equiaxed transition (CET) in Al-7Si alloy without and with an alternating electric current pulse (AECP). Without AECP, the macrostructure consists of typical columnar and equiaxed zones, separated by a near horizontal plane. As the AECP is applied during solidification, an additional fine equiaxed zone (FEZ) occurs in the as-cast macrostructure. From measured temperature profiles, cooling rate and temperature gradient are determined. It is found that CET occurs for a critical value of the cooling rate, which is observed to be about 0.14 K·s⁻¹ in the present investigation. Furthermore, the macrostructural observation with mold for embedding the mesh plate demonstrates that the major factor responsible for the formation of fine equiaxed grains is the detachment of crystal nuclei from the upper contact surface and the lateral wall. The detachment is in turn ascribed to electric current-associated free energy change (ΔG_e)-induced the driving force F.

In this study, the microstructural evolution and mechanical properties of TiCuNiZr-based bulk metallic glass (BMGs) composites were systematically investigated in order to optimize both the strength and the ductility of BMGs. By tailoring the glass-forming compositions, TiCuNiZr-based BMG composites with different volume fractions of B2 (Ti,Zr)(Cu,Ni) crystals precipitating in the glassy matrix exhibit not only macroscopic ductility but also high strength as well as work-hardening, which is due to the formation of multiple shear bands and martensitic transformation during deformation. Optimized mechanical properties can be achieved when the crystalline volume fraction is at least higher than 44 vol. %, which is attributed to the sizeable difference between Young’s moduli of the B2 (Ti,Zr)(Cu,Ni) crystals and the glassy matrix, and the precipitation of Ti₂Cu intermetallic compounds at the B2 crystal boundaries. Our study provides a complementary understanding of how to tailor mechanical properties of TiCu-based BMG composites.