Effect of Tensile Orientation on Rafting of γ' Phase in Single Crystal Ni-base Superalloy, CMSX-2

Abstract

Change in the shape in coarsening of the cuboidal γ' phase during creep of the single crystal nickel-base superalloy, CMSX-2, with the three different pole orientations, nearly [001], [011] and [111] to stress axes. The volume fraction of γ' precipitates was nearly equal to 70%. Creep tests were conducted at temperatures of 1173, 1273 and 1323K. At higher stresses, there were no significant differences in the time to rupture and the minimum creep rate between the [001] and [011] crystals, while, crystal with [111] orientation shows two times larger minimum creep rate. SEM observations of three planes for each single crystal were conducted as follows, for (001), (100) and (010) planes in [100] crystal, for (011), (100) and (011) in [011] crystal, and for (111), (211) and (011) in [111] crystal. Consequently, it is confirmed that the cuboidal γ' turns its shape to the platelet which is evolved along the (001) plane for three single crystals. TEM observations showed that the connection of cuboidal γ' occurred to [020] and [200] directions, and the γ' plate was formed parallel to (001) plane, irrespective to the crystal orientations. The rafting in the single crystals with [011] and [111] orientations to stress axis has not been reported. So the reason of the formation of the rafting in the single crystals with [011] and [111] orientations was discussed.