EFFECT OF SERRATED GRAIN-BOUNDARIES ON CREEP-RUPTURE PROPERTIES OF A WROUGHT COBALT-BASE ALLOY

Effect of serrated grain boundaries on the creep-rupture properties of 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 discussed based on a 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. Large differences in rupture ductility occurred at the lower temperatures. The results suggest that the strengthening effect is correlated to the change in the creep-fracture mechanism of specimens with creep-rupture test conditions.