13th International Conference on Fracture June 16–21, 2013, Beijing, China 6 4. Conclusions (1) Microstructures of Ti-6Al-4V alloy in the as-cast and post-HIPped condition were both lamellar colony structures. Following HIPping of the alloy, the thicknesses of lamellar plate and the alpha colony size both increased. Fracture toughness of the post-HIPped samples is higher than that of the as-cast samples. This was associated with the significant reduction in the volume fraction of pores by HIPping. The fracture mode changed from the intergranular fracture into transgranular fracture. (2) The fatigue crack growth rate of the post-HIPped sample with larger lamellar spacings was lower than that of the as-cast samples with smaller lamellar spacings. More crack deflections and branchings were found in the post-HIPped samples than in the as-cast samples, which indicates more energy was consumed in the fatigue crack propagation of the post-HIPped samples. Acknowledgements This work was partly sponsored by EU-China FP7 collaborative project (FP7-AAT-2010-RTD- CHINA). The authors also would like to acknowledge FalconTech, Wuxi, China for providing fatigue test machine and support during the experiments. Figure 8. Scanning electron micrographs of Ti64 alloy fatigue fracture surfaces: (a) (b)as-cast, (c) (d) post-HIPped. (a) (b) (d) (c) Striations Striations Secondary cracks Secondary cracks
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