Plasma Electrolytic Polishing of LPBF Ti-6Al-4V: Surface Integrity, Tensile Fatigue Behaviour of Solid Specimens, and FEA-Guided Stress Analysis of Gyroid Scaffolds

This study presents an integrated computational–experimental approach to enhance the tensile fatigue life of laser powder bed fusion (LPBF)-fabricated Ti-6Al-4V Gyroid scaffolds for orthopedic implants. Scaffolds with 60–80% porosity were designed, and finite element analysis (FEA) was employed to analyze localized stress distribution, mechanical behavior, and crack initiation sites under compression, bending, and tensile loading. The FEA results showed that elastic modulus (2.6–8.0 GPa) and compressive yield strength (85.5–251.3 MPa) aligned with human bone requirements. The bending and tensile FEA identified that tensile stress concentrations at exterior node surfaces promoted crack initiation. The LPBF-induced surface roughness further intensified these stresses, accelerating crack nucleation and compromising fatigue life. To address this, plasma electrolytic polishing (PEP) was applied at 240 V for 15, 20, and 25 min on the LPBF Ti-6Al-4V solid tensile specimens and Gyroid scaffolds. To evaluate the effect of PEP on surface integrity and fatigue performance, roughness and tensile fatigue tests were performed on LPBF Ti-6Al-4V solid tensile specimens rather than on porous scaffolds. The PEP for 20 min significantly reduced the average roughness (Ra) from 17.85 ± 1.27 µm (as-built) to 2.84 ± 0.45 µm, with an improvement of 84.10%, while also showing the smooth quality of the Gyroid scaffolds. Consequently, the enhanced surface quality led to a 30.46% increase in the average tensile fatigue cycles to failure (Nf) (σmax = 800 MPa and R = 0.1) of the solid specimens compared to the as-built condition. This improvement indicates the PEP’s effectiveness in enhancing the material fatigue life through surface defect elimination, serving as surface- and material-level supporting evidence for the potential fatigue life improvement of PEP-treated Gyroid scaffolds.