1990 Volume 76 Issue 1 Pages 113-119
Effect of serrated grain boundaries on the creep-rupture properties of a wrought cobalt-base HS-21 alloy are investigated in the temperature range from 1 089 K (816°C) to 1 311 K (1 038°C). The strengthening mechanism of serrated grain boundaries is then discussed based on the authors' grain-boundary fracture model, in which the recovery effect by diffusion of atoms is taken into account. Specimens with serrated grain boundaries showed higher creep-rupture strength and larger rupture ductility than those with normal straight grain boundaries. Especially, large difference in the rupture ductility occurred at the lower temperatures. A ductile grain-boundary fracture was observed on the specimens with serrated grain boundaries, but typical grain boundary facets were found in specimens with straight grain boundaries, except high-temperature low-stress conditions. The results of the theoretical discussions based on the model suggested that the strengthening effect of serrated grain boundaries is correlated to the change in the creep-fracture mechanism of specimens with the creep-rupture test conditions.
