Abstract
	The deformation and damage mechanisms in wrought nickel base superalloy EI 698 VD were investigated by examining the microstructure, crack nucleation and propagation mechanisms of representative specimens.  All tests, high temperature creep, isothermal cyclic creep, including pure fatigue, and cyclic creep with additional thermomechanical fatigue stress component were load controlled and have been conducted at high temperature of 650°C. The effect of individual testing hold periods representing cyclic frequency as well as combined effect of hold periods and thermomechanical fatigue stress effect were studied considering the role of superimposed fatigue stress component onto creep in deformation process. The fractured specimens were sectioned and examined by transmission electron microscopy to reveal deformation microstructure and active dislocation deformation mechanisms. Fractography examination of fractured specimens have shown that introduction of fatigue stress onto creep stress had been clearly proved to affect the crack nucleation process only for thermomechanical fatigue testing with shortest hold period and for pure fatigue.