Hot Cracking Susceptibility Prediction from Quantitative Multi-Phase Field Simulations with Grain Boundary Effects

Hot cracks are notorious defects in casting, welding, and additive manufacturing. Grain boundaries play a key role in cracking formation. Still, their effects are often neglected in hot cracking susceptibility predictions, and thus a quantitative picture of hot cracking susceptibility and liquid fracture is still lacking. In this work, we construct a multiorder parameter phase-field model for binary alloys solidification to simulate attractive, neutral, and repulsive grain boundaries in the thin-interface limit. Phase-field simulations with different combinations of grain boundary and bicrystal growth types are used to obtain solidification paths, which are then used as the input into the Rappaz, Drezet and Gremaud (RDG) model. We study the so-called Λ-shape variation of hot cracking susceptibility as a function of solute concentration, showing that the magnitude of the Λ curve peak shifts to higher values and to lower concentrations as grain boundary energy increases. Meanwhile, the peak magnitude becomes higher and shifts to a higher value and higher concentrations when convergent grain growth is applied. Furthermore, in all cases examined, the corresponding pressure drops predicted for hot cracking exceed the theoretical liquid rupture stress, consistent with experimental observations. These results demonstrate that quantitative phase-field simulations, when coupled with the RDG model, are capable of accurately predicting liquid rapture states relevant to hot cracking.