Journal of Materials Research and Technology (Jul 2024)
Effects of solidification shrinkage on solute segregation and hot cracking sensitivity in liquid channel during columnar dendrite growth
Abstract
Hot cracking is the most prevalent defect in the rapid solidification process of alloys, which seriously restricts the mechanical properties of the build. Solidification shrinkage is one of the key factors leading to hot cracking sensitivity, and it, together with tensile stress, causes pressure drops inside the liquid channel. However, the mechanism of solidification shrinkage on hot cracking is not clear. In this work, we established a non-equilibrium phase field model considering the density change during liquid-solid phase transformation. The effects of solidification shrinkage on the morphology and solute segregation of liquid channel in directional solidification were simulated by examples with different solid density. The solidification shrinkage will promote the release and diffusion of solute, leading to an increase in the proportion of high solute concentration liquid in the channel. The columnar dendrites continue to solidify, leading to a decrease in constitutional supercooling in the channel, thereby reducing the temperature at which the solid skeletons connect with each other. This results in the channel becoming narrow and elongated, increasing the hot cracking sensitivity. Finally, the solidification curves obtained from the phase field model and analytical model are input into the RDG (Rappaz, Drezet and Gremaud) model to predict the pressure drop in the system. The numerical results indicate that the maximum pressure drop in the channel occurs at the root and increases with solidification shrinkage. These results demonstrate that the phase field model, which takes into account the change of liquid-solid densities during phase transition, can accurately analyze the impact of solidification shrinkage on hot cracking sensitivity and the maximum pressure drop in the liquid channel.
