13th International Conference on Fracture June 16–21, 2013, Beijing, China 1 Influence of Microstructure on Fatigue Crack Propagation and Fracture Toughness of Large Ti-6Al-4V Cast Structure Xin Feng1,*, Anqi Wang2, Yingjie Ma1, Xinhua Wu3, Jiafeng Lei1, Yuyou Cui1, Rui Yang1 1. Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China 2. FalconTech, 99 Hongshan Street, The New District, Wuxi 214145, China 3. Department of Materials Engineering, Monash University, Wellington Road, Clayton, Victoria 3800, Australia * Corresponding author: xfeng12b@imr.ac.cn Abstract The study is part of research activities for EU-China FP7 collaborative project (FP7-AAT- 2010-RTD-CHINA): Casting of Large Ti Structures (COLTS) and has been carried out in order to investigate the influence of microstructure of cast Ti-6Al-4V large thin wall structure on fatigue crack propagation and fracture toughness. Some samples were post HIPped (hot isostatic pressed). The effects of grain morphology on fracture and fatigue crack propagation mechanism have also been studied. The fracture surface has been examined using scanning electron microscopy (SEM). The relationships between microstructure and fatigue crack propagation rate and fracture toughness were established and comparison has been made between the as-cast and post HIPped conditions. Keywords Ti-6Al-4V alloy, Hot isostatic pressing, Fracture toughness, Fatigue crack growth 1. Introduction Ti-6Al-4V alloy has been widely used in aerospace industry due to its low density, high specific strength, excellent combination of strength and toughness, and resistance to creep up to moderately high temperature. While Ti-6Al-4V alloy is mostly wrought processed, near-net-shape methods such as centrifugal investment casting are increasingly used, because the desired castings require no machining except the removal of flash around edges and possible drilling and tapping holes, which shortens the process and reduces the cost. The key issues associated with centrifugal investment casting are poor reliability and reduction in mechanical properties due to the formation of cavity and porosity during casting. These defects control the mechanical properties such as fatigue and fracture because of large stress concentration. The probability of failure due to stress concentration has been modeled by the Weibull distribution [1]. In an attempt to improve the fatigue life, the cast components usually were hot isostatically pressed (HIPped) [2], which is an effective compaction technique for the removal of internal defects such as porosity, shrinkage, and inter-dendritic cracks. Fatigue crack growth resistance and fracture toughness are important properties for aerospace applications and have been studied extensively [3]. Since HIPing plays a noticeable role in the improvement of fatigue properties, in the current study fatigue crack growth resistance and fracture toughness were investigated on both the as-cast and post-HIPped Ti-6Al-4V alloy. The obtained results were compared and the effect of post-HIPping was discussed to gain a better understanding of the influence of post-HIPping on fatigue crack growth resistance and fracture toughness of this alloy.
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