Abstract
A Ni-based superalloy CMSX-6 was directionally solidified at various drawing speeds (5–20 μm·s−1) and diameters (4 mm, 12 mm) under a 0.5 T weak transverse magnetic field. The results show that the application of a weak transverse magnetic field significantly modified the solidification microstructure. It was found that if the drawing speed was lower than 10 μm·s−1, the magnetic field caused extensive macro-segregation in the mushy zone, and a change in the mushy zone length. The magnetic field significantly decreases the size of γ’ and the content of γ-γ’ eutectic. The formation of macro-segregation under a weak magnetic field was attributed to the interdendritic solute transport driven by the thermoelectric magnetic convection (TEMC). The γ’ phase refinement could be attributed to a decrease in nucleation activation energy owing to the magnetic field during solid phase transformation. The change of element segregation is responsible for the content decrease of γ-γ’ eutectic.
Highlights
Nickel-based superalloys have been used for more than 30 years as materials for blades in aerospace turbine engines
In Figure 1d2–e2, with the application of a 0.5 T magnetic field in the solidification, some channel macro-segregation appears in the center of the specimen with the diameter of 12 mm and its quantity is gradually increased with increasing drawing speed
The above experimental results show that the application of a transverse magnetic field during the directional solidification of Ni-based superalloy can trigger the formation of macro-segregation
Summary
Nickel-based superalloys have been used for more than 30 years as materials for blades in aerospace turbine engines. Mechanical properties of nickel-based superalloys are closely related to their solidification microstructure, which mainly involves macro-segregation, γ’, γ-γ’ eutectic. The size, morphology and distribution of the γ’ precipitates significantly decide the mechanical properties of superalloys [1]. The γ-γ’ eutectic should be restrained because it depletes the formation element of the γ’ phase and reduces the start melt temperature [2]. The application of a uniform magnetic field in the area of solidification has attracted increasing attention [3,4,5,6]. It has been shown that the convection flows in a planar solid/liquid interfacial area can be significantly reduced by applying a magnetic field in the melts. Boettinger et al [7]
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