Influence of yttrium addition on high temperature oxidation resistance of single crystal superalloy

Two experimental single crystal superalloys Y-free alloy and Y-containing alloy were cast in the directionally solidified furnace, while other alloying element contents were basically kept unchanged. The isothermal oxidation behavior of two single crystal superalloy was studied at 1100 degrees C in ambient atmosphere. Morphology of oxides was examined by scanning electron microscopy (SEM) and their compostion was analyzed by X-ray diffraction (XRD) and energy dispersive spectroscopy. (EDS). The effect of yttrium on the high temperature oxidation resistance of the single crystal superalloy was investigated. The results showed that the oxidation resistance of Ni-base single crystal superalloy was substantially improved by adding a little amount of rare earth yttrium. Yttrium could promote the oxide of Al formation and decreased the proportion of NiO. Yttrium increased the coherence between the oxide scale and the alloy substrate to decrease the spallation of oxide scale. Yttrium reduced the oxide grain size and the thickness of oxide layer.