Fatigue crack growth in Selective Laser Melted Ti-6Al-4V

Abstract

This research investigates the effect of a varying build orientation and different heat treatment on the crack propagation properties of SLM Ti-6Al-4V. Both crack propagation rate and direction are investigated. Fatigue tests are performed with a constant cyclic load and single edge notch specimens. Ten unique types of specimens were tested by combining five different build orientation (0°, 30°, 45°, 60° and 90°) with two different heat treatments (Stress relieved and Hot Isostatic Pressing). In the end, similar crack propagation rates were measured for all specimens. Although, small differences were seen in the microstructure and DIC analysis, they did not seem to change the crack propagation rate. This observation led to the conclusion that the crack propagation rate is not influenced by a change in build orientation or a change in heat treatment. On the other hand, the measured crack paths showed some differences. Small crack deflections were found for 30° - SR and 45° & 60° - HIP, while all other specimens had cracks propagating in a direction normal to the applied stress. As only off-axis specimens showed repetitive crack deflections, it can be concluded that the anisotropic microstructure is causing this behaviour. However, no conclusive explanation could be given based on the data gathered in this experiment. It is expected that different mechanisms caused the crack deviations as it happened in both heat treatments but for different orientations. Further research in this specific field in needed to explain the measured behaviour.