RAPIDLY SOLIDIFIED MC CARBIDE MORPHOLOGIES OF A LASER-GLAZED SINGLE-CRYSTAL NICKEL-BASE SUPERALLOY

Rapidly solidified MC (TiC type) carbide morphology and its evolution with solidification cooling rate were studied comprehensively for a laser-glazed hot-corrosion resistant single-crystal nickel-base superalloy. The rapidly solidified interdendritic MC carbide was found in flower-like or radially branching morphologies which are closely related to the solidification cooling rate. At a relatively low cooling rate (9 X 10(3) K s-1), the carbide takes up the flower-like morphology, in which a few thick plates grow radially from the central nucleus. As the cooling rate increases, the growth morphology changes from flower like to radially dendritic and finally to well-developed radially branching colonies. The growth mechanism of the rapidly solidified MC carbide was confirmed to be lateral growth from the ledges or steps existing on the growing interface. The branching of the well-developed highly branching carbide occurs from the twins or twin intersections on the advancing fronts.