EFFECTS OF AGING AND STRESS AGING ON CREE P RESISTANCE OF SINGLE-CRYSTAL NI-BASE SUPERALLOY CMSX-4

Influence of the formation of rafted structure of gamma' phase on cree p resistance has been investigated using a single crystal nickel-base superalloy, CMSX-4. The rafted structure of gamma' was controlled by c onducting stress aging (creep test) at 1273K-160MPa up to 3.24 X 10(6) s. Aging without stress, called simple aging, was also performed at 12 73K up to 3.6 X 10(6)s. Cuboidal gamma' in the specimen as heat treate d turned to the rafted one during a transient creep stage of stress ag ing. In the simple aging, cuboidal gamma' became larger without changi ng their shape. The stress enhanced creep tests were conducted at 1273 K-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 th an those of as heat treated one. The TEM observation of specimens inte rrupted the stress enhanced creep test at minimum creep rate showed th at the stress aged specimens have the gamma region partially with high dislocation density which was not detected both in as heat treated sp ecimen and the simple aged ones. The larger minimum creep rate in the stress aged specimens with rafted structure of gamma' phase was caused by the increase in the width of the channel of gamma matrix.