The Effect of Grain Size on Fatigue Crack Propagation in Commercial Pure Titanium Investigated by Acoustic Emission

Abstract

The effect of grain size on fatigue crack propagation and the corresponding acoustic emission (AE) characteristics of commercial pure titanium (CP-Ti) were investigated at room temperature. After a four-point bending fatigue testing, the fatigue features and AE source mechanisms were discussed, combined with microstructural and fractographic observations. The results showed that the increased grain size had little effect on the stable propagation rate of fatigue crack; however, a significant increase in the AE counts rate was observed. During crack stable propagation, the relationship between the AE counts rate and the fatigue stress intensity factor range was generally in accordance with the Pairs law, with the exception of some local fluctuations due to regional twin paling. While lenticular twins appeared dispersively along the crack, twin palings were observed occasionally at the edge of the crack. Twin paling occurrence was more frequent in the specimens with larger grains than in those with smaller grains. This suggests that twin discontinuously played a role in the fatigue process in this CP-Ti, and that the AE technique is sensitive to crack propagation and twinning events during fatigue.