Abstract
The 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 particle cutting is the predominant bypassing mechanism.
Get full access to this article
View all access options for this article.