Fatigue crack growth behavior of 95Pb–5Sn solder under various stress ratios and frequencies

Fatigue crack growth tests of 95Pb–5Sn solder have been carried out at frequencies from 0.01 to 10 Hz and at stress ratios from 0.1 to 0.7. It was found that the stress ratio had no influence on fatigue crack growth behavior under the frequency of 10 Hz due to cycle-dependent crack growth without crack closure. The fracture manner was changing from transgranular to intergranular with decreasing frequency. Fatigue crack growth under the frequency of 0.01 Hz was predominantly intergranular and time-dependent, while that under frequencies of 1 and 0.1 Hz was of mixed type but still cycle-dependent. Dynamic recrystallization occurred during fatigue crack growth tests; the initial grain size was about 50 to 100 μm and that after testing was about 10 to 15 μm. This phenomenon will have a significant influence on the intergranular crack growth behavior.