Non-monotonic changes in critical solidification rates for stability of liquid-solid interfaces with static magnetic fields

Abstract

We report the magnetic field dependence of the critical solidification rate for the stability of liquid-solid interfaces. For a certain temperature gradient, the critical solidification rate first increases, then decreases, and subsequently increases with increasing magnetic field. The effect of the magnetic field on the critical solidification rate is more pronounced at low than at high temperature gradients. The numerical simulations show that the magnetic-field dependent changes of convection velocity and contour at the interface agree with the experimental results. The convection velocity first increases, then decreases, and finally increases again with increasing the magnetic field intensity. The variation of the convection contour at the interface first decreases, then increases slightly, and finally increases remarkably with increasing the magnetic field intensity. Thermoelectromagnetic convection (TEMC) plays the role of micro-stirring the melt and is responsible for the increase of interface stability within the initially increasing range of magnetic field intensity. The weak and significant extents of the magneto-hydrodynamic damping (MHD)-dependent solute build-up at the interface front result, respectively, in the gradual decrease and increase of interfacial stability with increasing the magnetic field intensity. The variation of the liquid-side concentration at the liquid-solid interface with the magnetic field supports the proposed mechanism.

Improvement in creep life of a nickel-based single-crystal superalloy via composition homogeneity on the multiscales by magnetic-field-assisted directional solidification

“…It would result in an increase in δ . The magnetic field intensity in this study was not sufficiently large to affect the k 0 and D 27 , 31 . Therefore, the δ increase brings about the enhancement of k e , which decreases the microsegregation of alloying elements.…”

“…The MHD effect plays a damping role in the melt, such as motion braking, convection stabilization, and free-surface shaping, which can affect the macrosegregation and inclusions for the melt ingots 18 , the impurity striation and microscopic uniformity for the semiconductor crystal 19 – 21 . The TEMC stems from the interaction of the magnetic field and the thermoelectric current at the liquid-solid interface and its affecting zone is near the interface 22 , 23 , 27 . It plays a stirring role at the interface’s front in the radial direction.…”

“…It plays a stirring role at the interface’s front in the radial direction. The appropriate magnitude of TEMC results in a stability in the liquid-solid interface 27 . However, the strong TEMC could modify the liquid-solid interface shape and the dendrite morphology, or induce the macrosegregation 22 – 24 , 45 , 46 .…”

“…It could modify the solid-liquid interface shape 22 , the dendrite morphology 23 , 24 , the solute distribution 25 , the stray-crystal formation 26 , et al . The appropriate microstirring effect of TEMC increase the liquid-solid interface stability 27 , 28 and flatness 29 and eliminated the radial macro-segregation in the crystal 30 . The thermoelectromagnetic force (TEMF) in the solid near the liquid-solid interface can induce the dendrite irregularity and instability of the liquid-solid interface 31 – 33 , even the freckles, and the composition striations 33 , 34 .…”

The Change of Mushy‐Zone Length of a Nickel‐Based Single‐Crystal Superalloy During the Static‐Magnetic‐Field‐Assisted Directional Solidification

“…The EMB effect can damp the convection of the melt and increase G in the mushy‐zone. The other is thermoelectromagnetic convection (TEMC), which generates a force F TEMC in the melt. It is believed that TEMC can promote flow in the melt and reduce G in the mushy zone.…”