Session: 03-04 Metals: Discontinuities and Defects

Paper Number: 94120

94120 - The Role of an Individual Lack-of-Fusion Defect in the Fatigue Performance of Additive Manu-Factured Ti-6al-4v Parts 

Additive manufacturing (AM) techniques have made AM Ti-6Al-4V (Ti64) parts a reality in many industries. However, despite the optimism, their poor fatigue performance, especially in high cycle regimes, is the major hurdle for the industry accepting it as mainstream. One of the reasons owes to the widely distributed internal defects inherent to the AM process, which create a hotbed for fatigue crack initiation. In the past decade, researchers conducted investigations on the fatigue performance of AM Ti64 alloys with gas porosities, as well as evaluating key features of gas porosities such as their size, location and geometry. However, available investigations on the lack of fusion (LOF) defect, which is regarded as the most detrimental defect, are very limited. Regarding this, we conducted the finite element analysis to evaluate the fatigue performance of Ti64 alloys with an individual LOF defect. Three different LOF defects directly scanned from AM Ti64 coupons using Micro-CT with different geometry features, have been numerically analysed. The fatigue life of the AM Ti64 parts with such defects are estimated using the strain-cycle curve. Their feature points, which dominate the fatigue lives, have been extracted and analysed. In addition, we compare the mechanical results (e.g., stress, strain, and concentration factors) of the LOF defects to the results of porosities that share the same projection areas, to reveal the detriment of LOF defects. Furthermore, we conduct a parametric study on the role of defect orientation, distance to the surface, and size in the fatigue life of AM Ti64 parts. The results provide a better understanding of the detriment of LOFs in AM Ti64 alloys, paving the way for further research of AM metallic alloys with internal defects, such as multi-defects interaction behaviours.

Presenting Author: Zongchen Li Empa-Swiss Federal Laboratories for Materials Science and Technology

Presenting Author Biography: Dr Zongchen Li works as a Postdoctoral Scientist and project leader at Empa, working on the fatigue and fracture mechanics of AM metallic parts with internal defects.

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