Abstract:The present work investigates how axial static magnetic field affects the solidification structure and the solute distribution in directionally solidified GCr18Mo steel. Experimental results show that grain refinement and the columnar to equiaxed transition is enhanced with the increases in the magnetic field intensity (B) and temperature gradient (G) and the decrease in the growth speed. This phenomenon is simultaneously accompanied by more uniformly distributed alloying elements. The corresponding numerical … Show more
“…The PMF may increase the nucleation rate and increase the probability of nucleus survival. It is generally believed that the electromagnetic force, electromagnetic vibration, and forced convection are favorable for grain refinement, such as a direct action of the electromagnetic force on the mushy zone is supposed to break the dendrites into small fragments owing to high shear stress [20][21][22]. However, it is not clear which mechanism dominates.…”
The effect of the pulsed magnetic field on the grain refinement of superalloy K4169 has been studied in directional solidification. In the presence of the solid-liquid interface condition, the distributions of the electromagnetic force, flow field, temperature field, and Joule heat in front of the solid-liquid interface in directional solidification with the pulsed magnetic field are simulated. The calculation results show that the largest electromagnetic force in the melt appears near the solidliquid interface, and the electromagnetic force is distributed in a gradient. There are intensive electromagnetic vibrations in front of the solid-liquid interface. The forced melt convection is mainly concentrated in front of the solid-liquid interface, accompanied by a larger flow velocity. The simulation results indicate that the grain refinement is attributed to that the electromagnetic vibration and forced convection increase the nucleation rate and the probability of dendrite fragments survival, for making dendrite easily fragmented, homogenizing the melt temperature, and increasing the undercooling in front of the solid-liquid interface.
“…The PMF may increase the nucleation rate and increase the probability of nucleus survival. It is generally believed that the electromagnetic force, electromagnetic vibration, and forced convection are favorable for grain refinement, such as a direct action of the electromagnetic force on the mushy zone is supposed to break the dendrites into small fragments owing to high shear stress [20][21][22]. However, it is not clear which mechanism dominates.…”
The effect of the pulsed magnetic field on the grain refinement of superalloy K4169 has been studied in directional solidification. In the presence of the solid-liquid interface condition, the distributions of the electromagnetic force, flow field, temperature field, and Joule heat in front of the solid-liquid interface in directional solidification with the pulsed magnetic field are simulated. The calculation results show that the largest electromagnetic force in the melt appears near the solidliquid interface, and the electromagnetic force is distributed in a gradient. There are intensive electromagnetic vibrations in front of the solid-liquid interface. The forced melt convection is mainly concentrated in front of the solid-liquid interface, accompanied by a larger flow velocity. The simulation results indicate that the grain refinement is attributed to that the electromagnetic vibration and forced convection increase the nucleation rate and the probability of dendrite fragments survival, for making dendrite easily fragmented, homogenizing the melt temperature, and increasing the undercooling in front of the solid-liquid interface.
“…The effect of ASMF on the CET in GCr18Mo steel during directional solidification at low growth speeds (5-20 μm/s) has also been investigated in our previous work. 22) The results have shown that the applied ASMF has enhanced the CET of GCr18Mo steel. However, the mechanism for the CET with ASMF is roughly described from a macro perspective.…”
Section: Introductionmentioning
confidence: 86%
“…More details regarding the experiment conditions are described in the work. 22) The morphology of the solidification microstructures was observed by optical microscopy (DM 6000M, Leica, Germany). The samples were cut-across the longitudinal section, polished, and etched in saturated solution of picric acid at 80°C.…”
The effects of an axial static magnetic field (ASMF) on the columnar to equiaxed transition (CET) during directionally solidifying GCr18Mo steel were investigated by experiment and numerical simulation. Experimental results show that the CET has been promoted by the increases of the magnetic field intensity and temperature gradient and the decrease of the growth speed. The corresponding numerical simulations verify that a thermoelectric magnetic convection in the melts and a thermoelectric magnetic force acting on the secondary dendrite neck are produced by the interaction between ASMF and a thermoelectric current. Compared the experimental results with the numerical simulations, the mechanism for the CET with ASMF demonstrates that the application of ASMF contributes to the transport of the fragments in the melts and detachment of dendritic side arms. Based on these results, we propose a process window for the CET of GCr18Mo steel with ASMF.
“…However, under the action of the low-frequency alternating magnetic field, the dendritic structure in the alloy was broken to shorten the length of the primary dendrite, which reduced the distance and difficulty of the residual liquid phase to feed. Studies [40,41] have shown that an equiaxed structure is more conducive to the flow of low melting phases between the crystals to eliminate segregation. When the microstructure of the structure tended to be equiaxed, the eutectic phase exhibited a uniform network distribution.…”
Herein, a hot tearing measured system with external excitation coil and a differential thermal analysis system with applied magnetic field were used to study the effects of low-frequency alternating magnetic field on the solidification behavior and hot tearing susceptibility (HTS) of the AXJ530 alloy under different magnetic field parameters. The hot tearing volume of the castings was measured via paraffin infiltration method. The microstructure of the hot tearing zone of the casting was observed using optical microscopy and scanning electron microscopy, and the phase composition was analyzed using X-ray diffraction and energy depressive spectroscopy. The experimental results show that the solidification interval of AXJ530 alloy was shortened and the dendrite coherency temperature of the alloy decreased with the increase in frequency of alternating magnetic field. Under appropriate magnetic field parameters, the electromagnetic force could enhance the convection in the melt to promote the flow of the residual liquid phase, refine the microstructure, and optimize the feeding channel in the late solidification stage, which reduced the HTS of the alloy. However, when the magnetic field frequency was increased to 15 Hz, the induced current generated excessive Joule heat to the melt. At this time, the thermal action of the magnetic field coarsened the microstructure of the alloy, resulting in an increase in HTS of the alloy.
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