Weidong Xuan

Experimental Evidence of the Effect of a High Magnetic Field on the Stray Grains Formation in Cross-Section Change Region for Ni-Based Superalloy During Directional Solidification

The effect of a high magnetic field on the stray grains in cross-section change region was investigated experimentally during directional solidification of superalloy. The microstructures showed that the high magnetic field significantly suppressed the stray grains formation in cross-section change region. Meanwhile, the temperature curves indicated that the nucleation undercooling was significantly increased in a high magnetic field. The effect of a high magnetic field on the stray grains was discussed based on the nucleation mechanism.

Effect of a High Magnetic Field on Microstructures of Ni-Based Single Crystal Superalloy During Seed Melt-Back

The effects of a high magnetic field on microstructures during seed melt-back of superalloy were investigated. Experimental results indicated that the high magnetic field significantly modified the melt-back interface shape and the melt-back zone length. In addition, stray grain on the edge of sample was effectively suppressed in the high magnetic field. Based on experimental results and quantitative analysis, the above results should be attributed to the increasing temperature gradient in a high magnetic field.

Columnar-to-Equiaxed Transition and Equiaxed Grain Alignment in Directionally Solidified Ni3Al Alloy Under an Axial Magnetic Field

The effect of an axial magnetic field on the solidification structure in directionally solidified Ni-21.5Al-0.4Zr-0.1B (at. pct) alloy was investigated. The experimental results indicated that the application of a high magnetic field caused the deformation of dendrites and the occurrence of columnar-to-equiaxed transition (CET). The magnetic field tended to orient the 〈001〉 crystal direction of the equiaxed grains along the magnetic field direction. The bulk solidification experiment under a high magnetic field showed that the crystal exhibited magnetic crystalline anisotropy. Further, the thermoelectric (TE) magnetic force and TE magnetic convention were analyzed by three-dimensional (3-D) numerical simulations. The results showed that the maximum value of TE magnetic force localized in the vicinity of the secondary dendrite arm root, which should be responsible for the dendrite break and CET. Based on the high-temperature creep mechanism, a simple model was proposed to describe the magnetic field intensity needed for CET:

Effect of a Transverse Magnetic Field on Stray Grain Formation of Ni-Based Single Crystal Superalloy During Directional Solidification

B \ge kG^{ - 1.5} R^{1.25}

Effect of a High Magnetic Field on γ′ Phase for Ni-Based Single Crystal Superalloy During Directional Solidification

B≥kG-1.5R1.25. The model is in good agreement with the experiment results. The experimental results should be attributed to the combined action of TE magnetic effects and the magnetic moment.

The mechanism of inclusion removal from molten steel by dissolved gas flotation

Stray grains which may appear during production of single-crystal blades, can severely deprave the performance of turbine blades. This investigation primarily explores the conditions of stray grains formed in DZ417G superalloy by using samples with varying cross sections. The effect of withdrawal velocities on the microstructure of DZ417G superalloy in directional solidification is investigated. It is observed that the growth direction of dendrites did not change, and no stray grain appears in the re-entrant corner at low withdrawal velocity. Nevertheless, the stray grains grow up when the withdrawal velocity is higher than 150μm/s. The temperature profiles in the region of the cross section change at different velocities are examined. The increase of undercooling in the corner of the cross section change leads to the formation of stray grains.

Alternating-magnetic-field induced enhancement of diffusivity in Ni-Cr alloys

The effect of a transverse magnetic field on stray grain formation during directional solidification of superalloy was investigated. Experimental results indicated that the transverse magnetic field effectively suppressed the stray grain formation on the side the primary dendrite diverges from the mold wall. Moreover, the quenched experimental results indicated that the solid/liquid interface shape was obviously changed in a transverse magnetic field. The effect of a transverse magnetic field on stray grain formation was discussed.

Measurement of contact angles at room temperature in high magnetic field

The nucleation undercoolings of non-magnetic metals like paramagnetic aluminium in high magnetic fields were measured by the differential thermal analysis technique. It was shown that the nucleation undercooling of pure aluminium increased with increasing the magnetic field, while its melting temperature was hardly changed. Based on the model of magnetic dipoles at the interface, it is proposed that the magnetic-field-induced interfacial energy mainly contributes to the increase in undercooling. The change in undercooling in the magnetic field is calculated theoretically, which is in comparison with experimental data. Additionally, the inhibition of atom diffusion in the magnetic field plays a role in the change of undercooling.