Influence of dislocation–precipitate interaction on low cycle fatigue resistance of Alloy 800 at 600°C

AbstractThe high temperature, low cycle fatigue behaviour of Alloy 800 has been investigated at 600°C. The results showed that a prior aging treatment of 1000 h in the temperature range 550–600°C improved the fatigue resistance as compared to solution treated material. The strengthening effect was particularly evident in material aged at 550°C. A microstructural investigation revealed that theγ′ precipitate dispersion, which formed intragranularly during aging, interacted very strongly with mobile dislocations. The relatively large γ′ particles formed in material aged at 600°C were bypassed according to the Orowan mechanism, whereas the small γ′ particles in material aged at 550°C were bypassed by particle cutting. Measurements of striation spacings showed that the high fatigue strength of material aged at 550°C was accompanied by a low crack propagation rate. The results can be rationalized in terms of reversibility of plastic flow at the crack tip, which can be expected to be more pronounced when partic...