Effect of composition-dependent anisotropy parameters on the dendrite formation patterns in Ni-Nb alloy

Solid-liquid interfacial energy and anisotropy parameters of Ni-Nb alloys were calculated using capillary fluctuation method for compositions up to 11.46 at.% Nb. Despite the large atomic size mismatch and energy asymmetry, the Ni-Nb system showed no anomalous interfacial energy behavior. Analysis of number density peaks near the interface, combined with comparisons to Al-Sm and Cu-Zr systems, revealed that low solubility contributes to misaligned atomic layers and altered interfacial energy, emphasizing the role of configurational entropy variations near the interface. Molecular dynamics simulations and Bridgman directional solidification experiments demonstrated a compositional-dependent morphological transition from 〈100〉 to seaweed structures as Nb content increased. Compact seaweed evolved into stable doubloon arrays exhibiting strong orientational order, splitting predominantly constrained near the 〈100〉 direction, as confirmed by the disperse density peaks around 〈100〉 pole in inverse pole figures. EBSD analyses further showed that growth misalignment with thermal gradient significantly influenced microstructures with doubloons and tilted seaweeds, while having minimal effect on straight 〈100〉 dendrites. This highlights the intrinsic role of composition-dependent anisotropy in destabilizing dendrite tips and driving microstructure transitions with Nb addition. Additionally, 3D phase field simulations clarified the triplon-based splitting mechanism in tilted seaweeds and highlighted differences between Ni-Nb doubloons and typical isotropic seaweed morphologies in Al-based alloys, focusing on the bigger 〈100〉 interfacial energy and lower 〈100〉 stiffness. The results emphasize that the residual 〈100〉 interfacial anisotropy shown on the orientation selection map could guide ordered splitting patterns despite an overall reduction in anisotropy strength.