High temperature tribological behavior of W containing diamond-like carbon (DLC) coating against titanium alloys

The current study has been undertaken to determine friction, adhesion and wear mechanisms of tribological coatings for elevated temperature applications of Ti–6Al–4V alloy. Sliding wear characteristics of diamond-like carbon (DLC) coatings and polycrystalline diamond (PCD) was studied and compared with those of conventional N-based coatings, which exhibited a high coefficient of friction (COF) due to titanium adhesion to the coating surface. Hydrogenated DLC (H-DLC) and W containing DLC (W-DLC) coatings offered low and stable COF values of 0.11–012 at 25 °C while the PCD had the lowest COF of 0.05 at 25 °C. At temperatures > 200 °C H-DLCʹs COF increased rapidly accompanied by high coating wear. At 100 °C W-DLC had a COF of 0.06 which increased to 0.46–0.54 between 200 °C and 300 °C similar to that of H-DLC. However, at 400 °C W-DLCʹs COF decreased to 0.07, and a low COF of 0.08 persisted at temperatures as high as 500 °C. The governing mechanisms of the low friction of W-DLC observed at elevated temperatures were revealed by studying the compositions of the coating surfaces and the transfer layers formed on Ti–6Al–4V. Raman spectroscopy indicated that at 25 °C the transfer layers were rich in carbon, whereas at 500 °C they consisted mainly of tungsten trioxide (WO3) that formed on W-DLCʹs surface.