Effect of Chemical Etching Time on the Fatigue behaviour of Ti-6Al-4V
produced by Laser Powder Bed Fusion
This study focuses on the evolution of the fatigue strength of L-PBF
produced Ti-6Al-4V as a function of the chemical etching finishing
process. The aim is to identify the critical fatigue crack initiation
mechanisms and the transitions between them in terms of the evolution of
the surface micro-geometry caused by the finishing process. This has
been done using three different geometries and six different surface
states, including the machined reference surface state. The evolution of
the crack initiation mechanisms, identified via SEM observations of the
fatigue failure surfaces, is then used to explain the evolutions of the
fatigue strength and the fatigue scatter, in both the finite and the
high cycle fatigue-life domains. As expected, chemical etching effects
the fatigue life via a polishing effect on the micro-geometry, which
directly influences both the finite and the high cycle fatigue domains.
It is shown that chemical etching makes it possible to obtain fatigue
strengths that are almost similar to those of the machined surface,
despite the fact that the roughness is higher, even after an optimal
etching time. However, it is also observed that etching cannot fully
counter the effects of large surface connected porosities (typically
lack-of-fusion) that lead to large surface cavities. Some minor scale or
size effects can also be noted between the different coupon geometries.
This does not modify the conclusions concerning the initiation
mechanisms and their effect on the fatigue life.