The effect of grain orientation on creep cavitation and early growth in copper bicrystals

• Cavities are more numerous and grow much faster in polycrystalline copper than in bicrystals, which is consistent with previous research on other FCC metals and alloys. • Both the level of macroscopic stress and the extent of slip on the dominant slip plane at the boundary determine the nucleation, stabilisation and early stage growth processes. • The nucleated cavity is faceted and grows initially as a result of dislocations gliding into the cavity, which further promotes the development of a faceted profile. • Once stabilised the cavity profile becomes smoother, but grows in a crack-like manner, suggesting that the rate of growth is controlled by surface diffusion. • The cavities are not equiaxed in the plane of the boundary and they experience different growth rates in different crystallographic directions. Creep cavitation in metals and alloys is an important failure mode for high temperature applications of stressed components. Despite extensive study, creep remains not fully understood, particularly the process of cavity formation and the early stage of growth. To contribute to this field, bicrystal beams of nominally pure copper have been prepared with the grain boundary oriented normal to the long axis of the beam. Tests were conducted using a constant load cantilever creep test at a temperature of 285 °C in a vacuum of 10 −10 Pa. Creep cavitation was observed in bicrystals of {0 0 1}/{0 0 1}, {1 1 1}/{1 1 1} and {0 0 1}/{1 1 1} orientation with a 22° rotation at the boundary. We evaluate these data with the aid of crystal plasticity finite element simulations to explore the effect of crystal orientation on cavity nucleation and early growth in the copper bicrystals. The influence of local stress state and slip activity on the cavity formation process is discussed and evaluated.