The bending fatigue behavior,the corresponding microstructure and fracture morphology of SLM Ti-6Al-4V al-loy were studied.The rolled Ti-6Al-4V alloy with the same chemical composition as the SLM sample was set for compar-ative study.X-ray diffraction(XRD),scanning electron micro-scope(SEM)with electron backscatter diffraction(EBSD)were used to analyze the microstructure of the alloy.The res-ults show that the three-point bending fatigue cracks initiate from stress concentration areas near the quasi-cleavage frac-ture 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,sec-ondary 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 concen-tration and the formation of micro-cracks,which led to the nuc-leation of fatigue cracks.Moreover,the macrozone had little hindrance to crack propagation,which is not conducive to the fatigue life of materials.
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