Oxidation Behavior of the Niobium-Modified MAR-M247 Superalloy at 1,000 A°C in Air

MAR-M247 superalloy has excellent mechanical properties and oxidation resistance. The aim of this work was to evaluate the oxidation behavior of a Nb-modified MAR-M247 superalloy (10.2 wt% Co; 10.2 W; 8.5 Cr; 5.6 Al; 1.6 Nb; 1.4 Hf; 1.1 Ti; 0.7 Mo; 0.15 C; 0.06 Zr; 0.02 B; Ni balance). The samples were subjected to oxidation tests in air at 1,000 A degrees C up to 240 h and the weight gain was measured every 24 h. The material in the as-cast condition as well as those from the oxidation tests were characterized with the aid of SEM/EDS and X-ray diffraction (XRD). The results showed that the n value and the parabolic rate constant (k) for the MAR-M247(Nb) superalloy at 1,000 A degrees C were about 0.1 and 2.8 x 10(-8) mg(2)cm(-4)s(-1), respectively. The microstructural characterization showed the formation of NiO oxides in the outer layer, Cr2O3, TiO2, CoO, (Ni,Co)Cr2O4 spinels, W20O58 and HfO2 particles in the intermediate layer and Al2O3 in the inner layer and in the gamma' depleted zone of the material.