On the tribological behaviour of mechanical seal face materials in dry line contact: Part II. Bulk ceramics, diamond and diamond-like carbon films

The evolving tribological demands of mechanical face sealing applications such as those associated with high-duty fluid seals and gas sealing technology are driving the need for the development of new and novel seal face material solutions. Under conditions where the combination of high pressure and high surface speeds create high levels of PV the seal designer will specify two hard faces, typically a combination of reaction bonded silicon carbide, alpha sintered silicon carbide or tungsten carbide. Work has been carried out here aimed at evaluating and increasing the understanding of the tribological nature of these hard face combinations and evaluating the potential of polycrystalline diamond (PCD) and diamond-like carbon (DLC) films. Experimentation has shown that under dry moderate contact conditions mild deformation-controlled wear takes place with a polishing of the contact surfaces. Progressively increasing the contact pressure was shown to eventually produce a transition to severe microcrack-controlled wear. Coating one of the contact surfaces with a PCD or DLC film modified the contact dynamics producing low friction coefficients and in the case of the PCD film shifted the wear transition to a much higher contact severity. A linear elastic contact model is developed that provides a framework for rationalising the results of this work and enables the key features of mechanical face seal design to be related to the critical tribological characteristics of the seal face material systems.