Grain refinement and dendrite morphology of superalloy K4169 during equiaxed growth under pulsed magnetic fieldOA

The grain refinement effect of superalloy K4169 under a low-voltage pulsed magnetic field(PMF)with different pulse frequencies and pulse voltages,at a superheat of 191℃,was investigated.The grains of the ingots are refined,decreasing from 3.9 mm without the application of PMF to 1.7 mm with PMF.Furthermore,the dendrite morphology undergoes a transformation,changing from well-developed branches to a global rosette pattern with rounded dendrite tips.However,it is worth noting that the secondary dendrite arm spacing increases under the influence of PMF.The refinement mechanism was investigated by quenching experiments and theoretical analysis under PMF.The high superheat of 191℃ results in a low cooling rate and a small thermal gradient during solidification,which promotes the survival of heterogeneous nuclei,leading to grain refinement.Additionally,evolutions in dendrite morphology are attributed to increased heterogeneous nucleation.When PMF is applied,the solidification structure is refined even under high superheat conditions.This leads to simultaneous improvements in filling ability and grain size refinement,offering promising applications for the practical manufacturing of thin-walled complex parts.