Fatigue crack initiation and fracture behavior of a copper bicrystal with a perpendicular grain boundary

By cyclically deforming a [5̄913]⊥[5̄79] copper bicrystal with a perpendicular grain boundary (GB), the fatigue crack initiation and fracture behavior were investigated. It was found that only the primary slip systems were activated on both G1[5̄913] and G2[5̄79] grains including the vicinity of the GB at axial plastic strain range of 1.8×10−4–2.56×10−3. By observing the surface and fractography, it was confirmed that the fatigue cracks always nucleated and propagated along the GB, and displayed an obvious tendency on different surfaces. On the front surface of the bicrystal, the intergranular cracking was more preferential than that on the lateral surface, even though the geometrical conditions among PSB, GB and stress axis on the lateral surface claimed to enhance cracking are more close to those proposed by Christ (Mater. Sci. Eng. A117 (1989) L25). Based on the experimental results above, the effect of the interaction of PSB with GB and stress axis on intergranular fatigue cracking in the bicrystal is discussed. It is suggested that Christ’s geometrical conditions for intergranular cracking might be further developed and the plastic strain incompatibility near the GB should play a more important effect on intergranular fatigue cracking.