Bending fatigue behavior of biomedical Ti-6Al-4V alloy prepared by selective laser melting

The bending fatigue behavior, the corresponding microstructure and fracture morphology of SLM Ti-6Al-4V alloy were studied. The rolled Ti-6Al-4V alloy with the same chemical composition as the SLM sample was set for comparative study. X-ray diffraction (XRD), scanning electron microscope (SEM) with electron backscatter diffraction (EBSD) were used to analyze the microstructure of the alloy. The results show that the three-point bending fatigue cracks initiate from stress concentration areas near the quasi-cleavage fracture surface, and then propagate inward.The bending fatigue life of SLM Ti-6Al-4V alloy was higher than that of rolled Ti-6Al-4V alloy. SLM Ti-6Al-4V internal hole defects led to stress concentration near the surface, resulting in fatigue crack nucleation. However, the random orientation α + β grains, secondary cracks, and holes in the SLM Ti-6Al-4V alloy delayed the crack propagation and improved fatigue life. As for rolled Ti-6Al-4V, the macrozone composed of a large number of α grains with approximate orientation caused the stress concentration and the formation of micro-cracks, which led to the nucleation of fatigue cracks. Moreover, the macrozone had little hindrance to crack propagation, which is not conducive to the fatigue life of materials.