Sliding wear behavior of borided TI6Al4V alloy under dry conditions and simulated body fluid (calf serum)

This work evaluates the wear behavior of borided Ti6Al4V alloy under simulated body fluid conditions using calf serum as the lubricant. Two distinct titanium boride layer thicknesses were judiciously formed at 1100 °C via powder-pack boriding under an inert argon atmosphere for durations of 5 and 20 h. X-ray diffraction identified the formation of both TiB2 and TiB phases. Optical microscopy measurements revealed layer thicknesses of 6 μm (TiB2) and 9 μm (TiB) for the 5-h boriding process, and 11 μm (TiB2) and 17 μm (TiB) for the 20-h treatment. Elemental distribution across the layer/substrate system was assessed using energy-dispersive spectroscopy. Instrumented Berkovich indentation determined the hardness of the TiB2 phase to be in the range of 25–27 GPa, while the TiB phase exhibited a hardness between 15 and 22 GPa. Linear reciprocating wear tests revealed severe abrasive wear rates for the untreated Ti6Al4V alloy (3.4 × 10 −4 mm 3 /Nm), which were drastically reduced to 4 × 10 −5 mm 3 /Nm for the longest boriding time, achieving wear rate reductions between 67 and 88 % for the borided Ti alloy. Conversely, in calf serum tests, the formation of a protein-rich biofilm effectively reduced the coefficient of friction to values below 0.07 across all evaluated materials. Raman spectroscopy confirmed this tribofilm was composed of denatured proteins (Amide I , II, III bands) and saccharides. However, the untreated Ti6Al4V alloy continued to exhibit severe abrasion. Remarkably, for the titanium borides, wear tracks were barely detectable (only polishing), quantifying nearly 100 % reduction in wear rate (apparent wear). Critically, this near elimination of wear was achieved by the rigid $TiB_2$ layer shifting the dominant wear mechanism from sacrificial boundary lubrication (on the native alloy) to a highly efficient hydrodynamic regime. • Calf serum lubrication reduces friction to below 0.07. • Boriding leads to ~100 % wear rate reduction in calf serum. • Lubricated tests show wear mechanism shifts to polishing • For lubricated tests, a 5 μm TiB2 layer effectively prevents wear in Ti 6 Al 4 V • TiB2 eliminated wear by shifting lubrication from boundary to hydrodynamic regime