pH-Dependent Long-Term Degradation and Mechanical Integrity of LPBF-Fabricated Porous Ti-6Al-4V in Hank’s Solutions with Different pH Values

Titanium alloys are widely used as bone graft materials due to their excellent corrosion resistance and biocompatibility. Implant failure can result from long-term exposure to body fluids and inflammation-induced pH decreases, both of which compromise the material’s corrosion resistance and mechanical stability. To address this issue, porous Ti-6Al-4V alloy was selected in this work. Immersion tests were conducted in Hank’s solution with different pH values (3, 5, and 7) for 90 days to simulate the in vivo microenvironment under various physiological conditions. The degradation behavior of porous Ti-6Al-4V alloy during the 90-day immersion period was systematically investigated using a combination of characterization techniques. The results indicated that TiO2, Ca3(PO4)2, and Ca(H2PO4)2 phases were formed on the surface of the after 90 days of immersion. Massive dissolution of TiO2 was observed in solutions with high H+ concentration (low pH). Ion release tests revealed that the concentration of titanium ions released was significantly higher in acidic solutions, suggesting that the passive film formed on porous Ti-6Al-4V alloy was unstable and prone to dissolution under acidic conditions. Consequently, a large amount of corrosion products accumulated on the specimen surfaces immersed in acidic solutions for a long duration. Moreover, the compression properties of the samples deteriorated after immersion. Specifically, the compressive strength decreased by 12.68 MPa, 11.67 MPa, and 5.84 MPa for sample immersed in solutions with pH = 3, 5, and 7, respectively. The significant reduction in compressive performance of the alloy in high H+ concentration solutions was attributed to the decreased compactness caused by ion release. The fracture mode of the porous Ti-6Al-4V alloy after immersion was identified as a mixed mode of ductile and brittle fracture.