Additive manufacturing (AM) has enabled the fabrication of extremely complex components such as porous
metallic lattices, which have applications in aerospace, automotive, and in particular biomedical devices.
The fatigue resistance of these materials is currently an important limitation however, due to manufacturing
defects such as semi-fused particles and weld lines. In this work a chemical–electrochemical surface treatment
(Hirtisation®) is used for post-processing of Ti-6Al-4V lattices, reducing the strut surface roughness (Sa) from
12 to 6 μm, removing all visible semi-fused particles. The evenness of this treatment in lattices with relative
density up to 18.3% and treatment depth of 6.5 mm was assessed, finding no evidence of reduced effectiveness
on internal surfaces. After normalising to quasi-static mechanical properties to account for material losses
during hirtisation (34%–37% reduction in strut diameter), the fatigue properties show a marked improvement
due to the reduction in surface roughness. Normalised high cycle fatigue strength increased from around 0.1 to
0.16-0.21 after hirtisation, an average increase of 80%. For orthopaedic implant devices where matching the
stiffness of surrounding bone is crucial, the fatigue strength to modulus ratio is a key metric. After hirtisation
the fatigue strength to modulus ratio increased by 90%, enabling design of stiffness matched implant materials
with greater fatigue strength. This work demonstrates that hirtisation is an effective method for improving the
surface roughness of porous lattice materials, thereby enhancing their fatigue performance.