Effect of ambient air on fatigue crack propagation in copper compact tension bicrystals

The effect of environment on fatigue crack propagation in copper compact tension (CT) bicrystals was examined. The role of the initial grain boundary (GB) structure is analyzed for bicrystals having Σ9 and Σ41 grain boundaries. It is shown that the GB is not necessarily a preferential site for crack propagation in vacuum. A crack introduced intergranularly in air may change its mode of growth to transgranular in vacuum. The relative importance of GB cracking compared with persistent slip band (PSB) cracking in vacuum is examined. The dominant mechanism of fracture is determined by two factors: the GB structure and the geometry of slip with respect to the GB orientation.