The tribological behaviour of Ti-15-3 β-titanium alloy treated by integrating bulk treatment with surface functionalisation (IBTSF) was systematically investigated under unlubricated, oil-lubricated, deionised water and simulated seawater conditions. Reciprocating sliding tests were performed against a WC ball under loads of 10 N or 20 N for 10,000 cycles. The results demonstrate that the tribological performance strongly depends on both the IBTSF treatments and the test environments. Under unlubricated conditions, the catalytic ceramic conversion treatments (C3TAu32 and C3TAg32) exhibited significantly lower friction and wear than the conventional ceramic conversion treatment (C2T32), owing to the self-lubricating effect of Au/Ag and the formation of thicker oxide layers. Hence, under the most severe unlubricated sliding condition (20 N), C3TAu32 reduced the wear factor by 99% compared with C2T32. In contrast, C2T32 showed superior wear resistance in oil, deionised water and simulated seawater because of its dense oxide layer and strong oxide/substrate bonding, while C3TAg32 suffered from corrosive wear in simulated seawater. Thus, C2T32 exhibited a wear factor 90% lower than C3TAg32 under simulated seawater. These findings establish application-oriented guidelines for selecting IBTSF treatments under different service environments, with C3TAu32 recommended for unlubricated applications and C2T32 for oil-lubricated and marine environments. The possible wear mechanisms are discussed to advance scientific understanding.

The growing demand for high-performance and long-service components for challenging and resource-intensive applications has driven the development of high-strength metastable β-titanium alloys with multifunctional surfaces. In this study, a novel surface engineering strategy, termed integrated bulk heat treatment with surface functionalisation (IBTSF), is introduced. This approach combines bulk aging treatment with catalytic ceramic conversion treatment (C3T) incorporating Ag or Au, thereby simultaneously imparting surface multifunctionalities (high hardness, desirable tribological properties, and high antibacterial efficacy) while also enhancing the bulk mechanical properties. To this end, the metastable β-titanium-alloy Ti–15V–3Al–3Cr–3Sn (Ti–15–3) was selected as a representative alloy, and C3T was catalysed using either Au or Ag. Under a load of 20 N, the Au-catalysed C3T achieved near-zero wear and a low, stable coefficient of friction (COF) of ~0.3, owing to the formation of a lubricating tribo-film. In contrast, Ag-catalysed C3T maintained stable tribological performance up to a load of 10 N while delivering high antibacterial efficacies of 99.878% and 99.999% against E. coli and S. aureus within 3–6 h of contact, respectively, through passive Ag-ion release. Both treatments also enhanced the bulk tensile strength by approximately 50%, increasing from 872±39 to 1,280±40 MPa. This combination of exceptional wear resistance, potent antibacterial activity, and improved mechanical strength offers a promising and efficient pathway to surface multifunctionalising metastable alloys for long-service, high-reliability applications.