Carbide formation in nickel-base superalloy MAR-M247 processed through scanning laser epitaxy (SLE)

Nickel-base superalloys develop high-temperature strength primarily due to the solid-solution-strengthening and the precipitation-strengthening mechanisms typically through cobalt/chromium and aluminum/titanium respectively. Certain other elements such as boron and zirconium are chosen for grain boundary strengthening. Such elements tend to segregate to the grain boundaries reducing the grain boundary energy and resulting in better grain boundary cohesion and ductility. Another form of grain boundary strengthening is achieved through the addition of carbon and various carbide formers. The carbide formers are responsible for driving precipitation of carbides at grain boundaries and thereby reducing grain boundary sliding. Various types of carbides such as blocky, elongated, and Chinese-script are possible in the microstructures of nickel-base superalloys depending on the composition of the superalloy and processing conditions. However, in the SLE fabricated MAR-M247, only blocky carbides were predominantly observed. Scanning electron microscopy and energy dispersive X-ray spectroscopy investigations were carried out and the carbides were found to be tantalum-rich. This work is sponsored by the ONR through grant N00014-14-1-0658.