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. Here
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
ρ/ρs 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 (σf,106/σy)
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 σf/E ratio is a key metric. After
hirtisation the σf/E 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.Comment: 10 figure