Influence of microstructures on microstructurally short fatigue crack initiation and propagation in the forged and rolled Ti-6Al-4V bars

抄録

In this study, the effect of microstructures on microstructurally short fatigue crack initiated naturally, and its propagation behavior is investigated in the rolled (R-950), and forged (F-950) Ti-6Al-4V alloys. Specifically, fatigue tests were conducted in a tension-compression fatigue machine. An automatic, in-situ observation system in combination with digital image correlation technique (DIC) is used to continuously track and record microscopic deformation behavior, and small fatigue crack opening-closing behavior. The R-950 Ti-alloy showed a lower fatigue crack propagation rate, and higher fatigue limit than the F-950 Ti-alloy. The major difference of the fatigue crack growth between the two alloys was found to be at the crack length below 200 μm i.e. short crack region. From the DIC analysis, it was determined that in both the alloys the crack opening was under the compressive stress, and it was increased with increase in length. Both the alloys showed almost same crack opening-closing curves at the short crack region of the crack length below 200 μm. Therefore, it is indicated that the difference in fatigue crack growth rate and fatigue limit is attributed to the microstructure of both the alloys.