Fatigue Crack Growth and Related Microstructure Evolution in Ultrafine Grain Copper Processed by ECAP

Fatigue crack growth tests were carried out using centre-cracked tensile (CCT) specimens of ultrafine grained (UFG) copper, aiming at clarifying microstructure evolution around the fatigue crack tip and at better understanding of fatigue crack propagation mechanisms. The fatigue crack growth tests revealed that UFG copper had the lowest threshold stress intensity factor range Delta K-th. On the other hand, the crack growth rates were almost identical among the UFG and conventional specimens tested at higher Delta K-1 regime. From the microstructure observation after the fatigue crack growth test, significant grain growth was detected in the intimate vicinity to the fracture surface in UFG copper. The size of the grown grains in the UFG copper increased with increasing stress intensity factor range and with the size of the cyclic plastic zone. [doi:10.2320/matertrans.MD201123]