Abstract
Using electron backscattered diffraction techniques (EBSD) and optical microscopy (OM), the grain selection and competitive growth in a new-designed high-efficiency two-dimensional (2D) selector during solidification of Ni-based single-crystal (SX) superalloys have been investigated with emphasis on the geometry of the selector part in this article. It is found that the efficiency of the grain selector depends greatly on the thickness and eccentric distance of the selector part. When the thickness is smaller than 3 mm, a single grain can be selected. After reducing this value, the grain selector becomes more effective. When the eccentric distance is larger than 8 mm, one grain can be selected. As the eccentric distance increases, the selector’s efficiency is optimized. Recommendations for optimizing the geometry of the selector part are provided.
Highlights
Owing to the elimination of grain boundaries (GB), single crystal (SX) blades of Ni-based superalloys exhibit excellent high-temperature performances, have been widely used in aero-engines and are being introduced into industrial gas turbines (IGTs) [1,2,3]
Prior studies [7,8,9,10,11,12,13] suggest that the geometries of the starter block and the selector part of grain selectors in particular can affect significantly grain selecting efficiency and the crystallographic orientation of the selected grain
The results obviously show the selection behavior of the selector part of the grain selector, and that smaller thickness and larger eccentric distance are more efficient in grain selection
Summary
Owing to the elimination of grain boundaries (GB), single crystal (SX) blades of Ni-based superalloys exhibit excellent high-temperature performances, have been widely used in aero-engines and are being introduced into industrial gas turbines (IGTs) [1,2,3]. In comparison with equiaxed (EQ) and directional solidified (DS) blades, the preferred crystallographic orientation of SX blades of Ni-based superalloys coinciding with the minimum in Young’s modulus is oriented parallel to the blades’ axis [4] For this reason, the creep performance can be optimized as long as the axis direction of SX blades approaches the orientation. Prior studies [7,8,9,10,11,12,13] suggest that the geometries of the starter block and the selector part of grain selectors in particular can affect significantly grain selecting efficiency and the crystallographic orientation of the selected grain. The dimension of selector should be maintained in a stable range to optimize the grain orientation and select a single crystal efficiently
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