Effect of Magnetic Field Configuration on Stray-Crystal Formation with Different Platform Sizes during Directional Solidification of Single-Crystal Superalloy

The magnetic field is an effective means to control the solidification structure and the defects of metal and semiconductor crystals. This work investigates the effects of Cusp magnetic field (CMF) and longitudinal magnetic field (LMF) on the stray-crystal formation in the platform regions during the directional solidification of single-crystal superalloy with the different cross section sizes. The application of CMF reduces the formation of platform stray-crystal, while LMF increases its generation. As the platform size increases, the stray-crystal ratio increases regardless of whether the magnetic fields are applied or not, the effectiveness of CMF increases, while that of LMF decreases. The reason that the effects of CMF and LMF on the platform stray-crystal formation could be attributed to the change of flow structure from the distribution characteristics of the thermoelectric magnetic force and the magnetic damping force near the liquid–solid interface.