Influence of the formation of rafted structure of γ' phase on creep resistance has been investigated using a single crystal nickel-base superalloy, CMSX-4. The rafted structure of γ' was controlled by conducting stress aging (creep test) at 1273K-160MPa up to 3.24×106s. Aging without stress, called simple aging, was also performed at 1273K up to 3.6×106s. Cuboidal γ' in the specimen as heat treated turned to the rafted one during a transient creep stage of stress aging. In the simple aging, cuboidal γ' became larger without changing their shape. The stress enhanced creep tests were conducted at 1273K-250MPa to evaluate the creep resistance of the stress aged specimens and the simple aged ones. There was little difference in the minimum creep rate between the simple aged specimens and as heat treated one. But minimum creep rates of stress aged specimens were always larger than those of as heat treated one. The TEM observation of specimens interrupted the stress enhanced creep test at minimum creep rate showed that the stress aged specimens have the γ region partially with high dislocation density which was not detected both in as heat treated specimen and the simple aged ones. The larger minimum creep rate in the stress aged specimens with rafted structure of γ' phase was caused by the increase in the width of the channel of γ matrix.
