Influence of nanostructured solid lubricants on friction, wear, and surface topography during SPIF of CP-Ti Grade 2 implant

Single point incremental forming has emerged as a promising method for the customized fabrication of titanium biomedical components. However, severe tool–sheet interaction during single point incremental forming can lead to high friction, tool wear, and surface degradation, compromising implant performance and long-term biocompatibility. To address these challenges, this study investigates the tribological behavior and surface topography of commercially pure titanium Grade 2 using different families of nanostructured solid lubricants, including ceramic (ZrO 2 ), polymeric (polytetrafluoroethylene), transition metal dichalcogenide (MoS 2 ), and carbon-based (graphene) lubricants. The lubricants were characterized using scanning electron microscopy and energy-dispersive spectroscopy to confirm their morphology and elemental composition. Tribological performance was evaluated using pin-on-disk tests with titanium Grade 2 as the disk material and tungsten carbide as the counterface pin. The results revealed a clear performance hierarchy among the nanostructured solid lubricants. MoS 2 exhibited the lowest coefficient of friction (0.12) and wear rate (1.6 × 10 −4 mm 3 /N·m), followed by polytetrafluoroethylene (coefficient of friction: 0.15; wear rate: 2.3 × 10 −4 mm 3 /N·m), graphene (coefficient of friction: 0.16; wear rate: 3.4 × 10 −4 mm 3 /N·m), and ZrO 2 showing the highest friction (0.27) and wear rate (3.9 × 10 −4 mm 3 /N·m). Wear track analysis confirmed these trends, with MoS 2 producing the smallest wear track width (549.75 µm) and ZrO 2 the widest (1195.24 µm). Scanning electron microscopy observations indicated distinct wear mechanisms: ZrO 2 promoted abrasive wear, graphene exhibited mixed adhesive and lamellar sliding behavior, polytetrafluoroethylene formed a stable transfer film, and MoS 2 generated a protective lamellar tribofilm. Surface topography analysis of single point incremental forming-formed components showed that MoS 2 produced the best surface finish (Ra = 1.289 µm), followed by polytetrafluoroethylene (Ra = 1.579 µm), graphene (Ra = 2.259 µm), and ZrO 2 (Ra = 4.063 µm). Although MoS 2 exhibited superior tribological performance, polytetrafluoroethylene exhibited stable transfer-film-assisted lubrication, and based on its reported biocompatibility, remains a potential lubricant pending biological validation.