Directional solidification of monocrystal superalloy by electron beam floating zone-melting

Abstract

With the development of the aircraft engine, the monocrystal superalloy with homogeneous microstructure, low segregation and high purity is desired. This can be achieved by increasing the cooling rate under high vacuum condition to obtain the dendritic microstructure with superfine primary arm spacing. Using the electron beam floating zone-melting (EBFZ) technique, the single crystals of DD3 superalloy, having alternately planar, cellular and dendritic S/L interface, have been prepared by the seed crystal method in this paper. The misorientation between the single crystal's [100] crystallographic direction and the crystal growth direction is less than 10°. The interface morphology evolution is investigated. It can be seen that, when the zone melting rate is 100 μm/s, the primary dendrite arm spacing is five times smaller than that of the original seed. Meanwhile, the γ′ phase and the γ/γ′ eutectic are all fined and the microsegregation of the alloy elements decreased. The technical experiments show that, with carefully regulating the heating power and the zone melting rate, the melting zone can be kept stable. When the zone melting rate is small, the heating power can be increased in order to increase the temperature gradient. Whereas, when the zone melting rate is large, the heating power must be decreased in order to keep the growth processing steady.