Coarse Columnar Dendrites of GH3039 Nickel-Based Alloy at Diverging Grain Boundaries during Wire and Laser Additive Manufacturing: A Phase Field Simulation

Coarse columnar dendrite greatly reduced the mechanical performance of GH3039 nickel-based alloy in the additive manufactured parts, which limited its application in the engineering fields. This study provides a comparison of overgrowth behaviors at diverging grain boundaries through two-dimensional phase field simulation, and the effect of dendrite orientation on overgrowth behavior was analyzed. Moreover, our results show that the primary spacing becomes larger as the increasing of dendrite orientation. The columnar dendrites branch new dendrites near grain boundaries to refine the primary arm spacing in the process of wire and laser additive manufacturing (WLAM).

On Directional Dendritic Growth and Primary Spacing—A Review

The primary spacing is intrinsically linked with the mechanical behavior of directionally solidified materials. Because of this relationship, a significant amount of solidification work is reported in the literature, which relates the primary spacing to the process variables. This review provides a comprehensive chronological narrative on the development of the directional dendritic growth problem over the past 85 years. A key focus within this review is detailing the relationship between key solidification parameters, the operating point of the dendrite tip, and the primary spacing. This review critiques the current state of directional dendritic growth and primary spacing modelling, briefly discusses dendritic growth computational and experimental research, and suggests areas for future investigation.

A Simplified Scaling Law of Cell-Dendrite Transition in Directional Solidification

To describe the cell-dendrite transition (CDT) during directional solidification, a new simplified scaling law is proposed and verified by quantitative phase field simulations. This scaling law bears clear physical foundation with consideration of the overall effects of primary spacing, pulling velocity, and thermal gradient on the onset of sidebranches. The analysis results show that the exponent parameters in this simplified scaling law vary within different systems, which mediates the discrepancy of exponent parameters in previous experiments. The scaling law also presents an explanation for the destabilizing mechanism of thermal gradient in sidebranching dynamics.

Tilted Dendritic Growth Dynamics and Dendrite to Degenerate Seaweed Transition in Directional Solidification: Insights from Phase-Field Simulations

In this paper, we review our results from phase field simulations of tilted dendritic growth dynamics and dendrite to seaweed transition in directional solidification of a dilute alloy. We focus on growth direction selection, stability range and primary spacing selection, and degenerate seaweed-to-tilted dendrite transition in directional solidification of non-axially orientated crystals. For growth direction selection, the DGP law (Phys. Rev. E, 78 (2008) 011605) was modified through take the anisotropic strength and pulling velocity into account. We confirm that the DGP law is only validated in lower pulling velocity. For the stability range and primary spacing selection, we found that the lower limit of primary spacing is irrelative to the misorientation angle but the upper limit is nonlinear with respect to the misorientation angle. Moreover, predicted results confirm that the power law relationship with the orientation correction by Gandin et al. (Metall. Mater. Trans. A. 27A (1996) 2727-2739) should be a universal scaling law for primary spacing selection. For the seaweed-to-dendrite transition, we found that the tip-splitting instability in degenerate seaweed growth dynamics is related to the M-S instability dynamics, and this transition originates from the compromise in competition between two dominant mechanisms, i.e., the macroscopic thermal field and the microscopic interfacial energy anisotropy.

Investigation on the Morphological Instability during Directional Solidification of a Transparent Alloy during Sounding Rocket Flights

The movement and morphological change of a solid-liquid interface in directional solidification was investigated during two sounding rocket flights. By using the transparent binary alloy Succinonitrile-Acetone the dynamic processes at the solidification front could be observed directly. Both the planar interface growth, the onset of instability and the characteristic features of the interface morphology, i.e. the evolution of the primary spacing and amplitudes of the cells and dendrites were evaluated. The comparison with a calculation of the morphological instability based on the theoretical model of Warren and Langer showed a good agreement concerning the critical time and velocity of the solidification front.