Effect of the build direction on defect distribution and crack initiation of LPBF TI6AL4V

icaf2023 Tracking Number 66

Additive manufactured (AM) Ti6Al4V titanium alloy has a potential market in aerospace and biomedical industries due to its excellent corrosion resistance and high specific strength. Compared with the conventionally manufactured parts, a relatively better static mechanical performance of AM metal materials has been achieved by the optimized processing parameters. However, the defects in AM metal alloy cannot be eliminated thoroughly, and then this can lead to the degradation of fatigue properties and the anisotropic mechanical response. A comprehensive study on the defect characterization and its effect on crack initiation behaviour were performed in this paper. Laser powder bed fused (LPBF) Ti6Al4V titanium alloy in 0°, 45°, and 90° build directions were designed and manufactured. The defects were measured based on X-ray computed tomography and reconstructed using the Dragonfly software. The defect distributions along the build direction, the scanning direction, and the radial direction were compared. Defect size, sphericity, and defect orientation were characterized. Finally, the real defects were extracted and imported into a finite element model, effects of the defect orientation and the porosity on crack path were analysed. It was shown that porosity of the as-built samples decreased with the increasement of the build direction, and stress relieving process can cause the coalescence of small defect and higher porosity. The lack of fusion defects is prone to growing along the build direction. The defect size distribution can be fitted by the lognormal function, while the sphericity distribution of defects was fitted by the two-phase exponential growth function. The crack initiation site was controlled by the defect orientation and the effective bearing aera.