SOLIDIFICATION MORPHOLOGY AND SEMISOLID DEFORMATION IN THE SUPERALLOY RENE-108 .3. EQUIAXED SOLIDIFIED MICROSTRUCTURES

A high-temperature nickel-base superalloy (Rene 108) was solidified at various cooling rates. The morphology of the equiaxed microstructure and the mechanism for intrinsic microporosity formation were correlated to the processing parameters. A special Gleeble testing procedure (developed previously - where the samples were quickly raised to a predetermined temperature in the semisolid zone and fractured) was used for the measurement of the fracture data. The upper coherent temperature was noted to be a function of the solidification variables. The amount of strain accommodation and the hot-tearing resistance was found to be influenced by the solidification microstructure. The hot ductility, the semisolid strength, and the corresponding microstructural changes are examined and discussed. Fracture maps which include the temperature, transverse-fracture stress and cooling rate during solidification (T-sigma(T)-T) for the equiaxed solidified microstructures are presented. A castability map was created from the fracture data.