Phase Analysis of a Laserglazed Rene’N4 Superalloy

It is the first time that the phases in laserglazed single crystal nickel-base superalloy Rene'N4 have been studied systematically. The results show that there are three kinds of carbides and finely dispersed gamma' phase, as well as the gamma/gamma' eutectic in the microstructure, and the carbides are f.c.c TiC, TaC and hexagonal WC. These carbides and gamma/gamma' eutectic are distributed in the interdendritic regions. The cooling rate strongly affects not only the morphology of TiC but also the morphology and size of the gamma' phase. The morphology of TiC changes from the as-cast blocky form to dendritic and finally to a well-branched chrysanthemum-like form as the cooling rate is increased. At the same time, the size of gamma' becomes smaller and the morphology of gamma' changes from cubic to rounded-cubic. After rapid solidification, the as-cast well-developed mushroom-like gamma/gamma' eutectic alters into featherlike. The existence of gamma' and gamma/gamma' eutectic indicates that their precipitation rates are too large to be able to suppress their precipitations under a rapid solidification condition.