Additively manufactured (AM) alloy usually inevitably contains defects
during the manufacturing processor or service process. Defects, as a
harmful factor, could significantly reduce the fatigue performance of
materials. This paper shows that the location and introduced form of
defects play an important role in high cycle and very high cycle fatigue
(VHCF) behavior of selective laser melting Ti-6Al-4V alloy. S-N curve
descends linearly for internal defects induced failure. While for
artificial surface defects induced failure, S-N curve descends at first
and then exhibits a plateau region feature. We also observed
competition of interior crack initiation with the fine granular area
feature in VHCF regime. The paper indicates that only the size or the
stress intensity factor range of the defect is not an appropriate
parameter describing the effect of defects on the fatigue crack
initiation. Finally, the effect of artificial surface defects on high
cycle and VHCF strength is modeled, i.e. the fatigue strength
σ, fatigue life N and defect
size area (square root of projection area of defect
perpendicular to principal stress direction) is expressed as σ =
CN ( area)
for N and
σ = CN (
area) for
N≥N, where C, a and
n are constants, N is the number of
cycles at the knee point.