Abstract: High temperature crack propagation and fracture behavior of disks produced by six superalloys have been studied. Crack propagation rates were determined at 650 creep, fatigue and creep/fatigue interaction conditions. The crack propagation rate is raised with increasing strength of superalloy and is also increased with the dwelling time at maximum stress level of cyclic creep test condition. Crack propagation behavior is closely related to high temperature ductility (such as creep strain and stress rupture elongation). Ductility improvement can increase crack propagation resistance by means of softening heat treatment, controlling grain boundary precipitate and microalloying treatment (such as Mg addition to superalloy). \=

Key words: crack propagation, fracture, superalloy, magnesium