Multilayered diamond mechanical seal rings under biodiesel lubrication and the full sealing conditions of pressurized water

A mechanical sealing tribosystem based on multilayer microcrystalline/nanocrystalline diamond (MCD/NCD) coatings is proposed. The tribological behaviour was investigated in ring-on-ring self-mated planar contact configuration. Tests were carried out under biodiesel lubrication and pressurized water (2 bar) sealing conditions. A 3D optical confocal profilometer was used to obtain for the first time the wear coefficients of seal rings, revealing a value of k=6.3×10−10 mm3/N.m for biodiesel lubrication that is two orders of magnitude lower than for reciprocating sliding ball-on-flat experiments. The advantage of the multilayer strategy was demonstrated in the sealing of pressurized water, where full sealing conditions were achieved within the P×V range of 0.75-5.5 MPa ms−1. For these coatings, full delamination is prevented due to structural discontinuity at the MCD/NCD interfaces whereas for a MCD monolayer coating, premature failure takes place and sealing is not reached.