A COMPARATIVE STUDY ON THE SINGLE CRYSTAL GROWTH OF CMSX-4 VIA THE VERTICAL BRIDGMAN AND VERTICAL BRIDGMAN WITH A SUBMERGED BAFFLE

摘要

Convective cells due to thermal and solutal gradients above the solid/liquid (s/l) interface lead to instability or freckle formation which generally results in the breakdown of single crystallinity while solidifying superalloys directionally. To overcome this problem, a novel modification of the traditional Vertical Bridgman (VB) technique is utilized. This new Vertical Bridgman technique with a submerged baffle (VB-SB) makes use of a ceramic baffle that is submerged into the melt near the s/1 interface to decrease the melt height which leads to reduction of natural convection. Crystals of commercial CMSX-4 superalloy have been grown by both the traditional VB technique and VB-SB technique with various withdrawal velocities. Results are evaluated to establish a comparison basis between VB and VB-SB in terms of interface morphology, dendrite dimensions, and segregation.