EFFECT OF ELECTROMAGNETIC MELT TREATMENT NEAR LIQUIDUS ON THE FORMATION OF NON-DENDRITE MICROSTRUCTURE OF SUPERALLOY
GAO Zhongtang, HU Rui(), WANG Jun, YANG Jieren, LI Jinshan
State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072
Cite this article:
GAO Zhongtang, HU Rui, WANG Jun, YANG Jieren, LI Jinshan. EFFECT OF ELECTROMAGNETIC MELT TREATMENT NEAR LIQUIDUS ON THE FORMATION OF NON-DENDRITE MICROSTRUCTURE OF SUPERALLOY. Acta Metall Sin, 2014, 50(12): 1471-1477.
The effects of electromagnetic field and melt treatment near liquidus on the grain refinement of the Ni-20Cr-18W (mass fraction, %) superalloy have been studied. The average grain size of 60 kg ingot can be refined to 127 μm and the grains are both ?ne and globular. Based on the effect of electromagnetic field on atomic cluster, interface stability and transformation from dendritic grain to globular grain, the mechanism of grain refinement has been studied from the aspect of nucleation thermodynamics by OM, SEM, EBSD. The results show that electromagnetic melt treatment near liquidus results in signi?cant re?nement. The grain refinement can be attributed to the mechanism that atomic clusters and globular structures can become the nucleus when the initial undercooling reaches certain level. Electromagnetic field not only improves homogeneity of the macroscopic temperature field, but also plays a positive role in interface stability and dendritic to globular transformation, which increases the nucleation rate.
Fund: Supported by National Basic Research Program of China (No.2011CB610404), Program of Introducing Talents of Discipline to Universities (No.B08040) and Research Found of the State Key Laboratory of Solidification Processing China (No.62-TP-2011)
Fig.1 Schematic showing details of SEM and EBSD analysis on 60 kg grain refinement ingot in Ni-20Cr-18W superalloy
Fig.2 Transverse section EBSD images for samples No.2 (a) and No.3 (b) of Ni-20Cr-18W superalloy in Fig.1b
Fig.3 Schematic of sampling locations along longitudinal section of 60 kg melt at 2500 Hz and 17.6×106A/m2 (a), and temperature fields of different locations along axial (b) and radial (c) directions
Fig.4 OM microstructures of Ni-20Cr-18W superalloy held isothermally at different temperatures
Fig.5 Schematics of Peltier heating on solid/liquid interface of dendritic grain
Fig.6 Schematic of interactions between atomic clusters and globular grains
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