Optical Microscopy on Machined Surfaces in Ti-6Al-4V Reveals Pore Statistics that Correlate with Fatigue

Abstract Optical microscopy on the machined surfaces of 4-point bend fatigue samples 3D printed in Ti-6Al-4V is used to characterize pores larger than ≈15 microns. A large enough number of distinct scan speeds and fatigue tests that span the process window provides a statistically useful dataset. The variation in stress at which runouts (to 10 million cycles) are observed is anti-correlated with the pore density and the same inverse relationship exists for the maximum pore size observed within the area exposed to maximum tensile stress in each test. Total fatigue life is also anti-correlated with maximum defect size albeit with considerable scatter.