The influence of building direction on the fatigue crack propagation behavior of Ti6Al4V alloy produced by selective laser melting

Additive Manufacturing (AM) which combines with computer aided design, materials processing and forming technologies can manufacture near net shape components. In recent years, many studies have revealed the effects of AM parameters on metal material microstructures and mechanical properties. Few studies focus on the fatigue performance of AM materials. Therefore, in the present study, the Ti6Al4V samples produced by Selective Laser Melting (SLM) were used for in-situ fatigue tests. The effects of SLM building directions (0 degrees, 45 degrees, 90 degrees) on sample fatigue properties were investigated. The in-situ scanning electron microscope (SEM) observation technology was applied to observe the fatigue crack initiation and propagation behavior. An obvious worse crack propagation resistance of the 90 degrees samples can be identified. The fracture mechanism of SLM samples was also revealed. The results indicated that the fatigue small cracks always extend between paralleled alpha laths. The fatigue crack propagation direction can also deflect an angle accompanied with alpha colonies boundaries. Inter-granular fracture was predominant. For long cracks, the inhibition effect of microstructures can be ignored. Fatigue cracks can penetrate alpha colonies directly. Intra-granular fracture can be observed. At last, a simplified fatigue life evaluation of AM aero-engine blades was conducted. The fatigue life difference of blades resulted from different building directions was proved. The evaluation method of complex AM component building directions was provided. The best fatigue damage tolerance performance can be obtained.