A NEW METHOD OF FINE-GRAINED CASTING FOR NICKLE-BASE SUPERALLOYS

The grain structures and microscopic features of a nickle-base Inconel 738LC were examined under various melting and casting conditions. Res ults show that the gain size of the gamma matrix is reduced significan tly by a treatment of lowing melt superheat temperature (LMST). By the addition of a trace intermetallic compound AlxNiy to the melt togethe r with LMST treatment, a remarkable refinement could be obtained. The grain size over the whole section of castings could be refined to 0.5- 0.8 mm, i.e. to ASTM grain size M11-12. In addition, the size of prima ry MC carbides in the alloy is reduced. The secondary dendrite arm spa cing and phase constitution of the alloy are less sensitive to the add itions. (C) 1998 Elsevier Science S.A. All rights reserved.