Ultraprecision Machining of Additively Manufactured Ti-5Al-5Mo-5V-3Cr Alloy for Biomedical Applications

Abstract Titanium (Ti) and Ti-based alloys are widely used in biomedical implants due to their superior mechanical properties, corrosion resistance, and biocompatibility. Ti-6Al-4V (Ti64) is the most common alloy for bone implants, but its high elastic modulus (113 GPa) greatly exceeds that of natural bone (14–20 GPa), leading to stress shielding and implant loosening. To mitigate this issue, β-stabilized Ti alloys, which have a lower elastic modulus, are preferred. Ti-5Al-5Mo-5V-3Cr (Ti-5553) is a promising β-metastable alloy with an elastic modulus of 72 GPa, closer to that of bone. Unlike Ti64, Ti-5553 does not undergo martensitic transformation, preventing brittle phase formation. This makes it well-suited for additive manufacturing (AM), particularly laser powder bed fusion (LPBF), which enables the fabrication of patient-specific implants with improved functional fit. Beyond material selection, implant surface characteristics play a crucial role in osseointegration. Optimized surface structures promote cellular interaction, leading to stable, long-term integration. Ultra-precision machining is a viable technique for refining implant surfaces by creating microstructured features with superior finishes, enhancing biocompatibility while remaining cost-effective and precise. This study investigates the ultra-precision machinability of LPBF-built Ti-5553, focusing on the effects of depth of cut on tool wear, cutting force, chip morphology, surface roughness, and profile accuracy. Results show that flank wear was more significant than rake wear, progressively increasing with cutting distance. Cutting and thrust forces rose gradually, with shearing as the dominant material removal mechanism. Chips exhibited serrated patterns on the free surface and smooth sliding marks on the back surface. Surface roughness increased over the cutting distance, while tool wear negatively impacted tool geometry accuracy, cutting resistance, and surface finish. These findings highlight the potential of ultra-precision machining to enhance LPBF-built Ti-5553 implants by refining surface features and improving osseointegration, supporting its use in next-generation biomedical implants.