The impact of surface orientation on surface roughness and fatigue life of laser-based powder bed fusion Ti-6Al-4V

As-manufactured surface roughness is detrimental to the fatigue life of laser-based powder bed fusion (LB-PBF) Ti-6Al-4V components. Despite the criticality of surface roughness to the fatigue failure mode, the relevant test data is incomplete, for example with regard to the distinct effects of upward and downward-facing surfaces. This research characterises the relationship between the manufactured inclination angle, surface roughness and associated fatigue performance of LB-PBF Ti-6Al-4V. Unique to this research is the quantified difference in fatigue performance due to either or upward or downward-facing surface roughness; an outcome made possible by isolating the as-manufactured surface roughness of upward and downward-facing surfaces of inclined specimens prior to fatigue testing. Experimental results confirm the criticality of downward-facing surface roughness, and for the first time characterises the impact of surface orientation (upward and downward) on observed fatigue life. In addition to providing robust design data for LB-PBF Ti-6Al-4V, the underlying test method developed can be applied in future research to characterise the effect of orientation on fatigue. [Display omitted] •Removing downward-facing roughness improves fatigue life by >35% at ∼210 MPa.•Modified stress intensity factor determined using surface roughness.•Modified stress intensity factor has strong correlation with fatigue life.•Finite element analysis matches stress concentrations with crack initiation sites.