A Variable Hardness PVD Coating – A Paradigm Shift For Running-In

Rings & liners must run-in before reaching optimum performance & oil control. A top softer run-in coating is better for removing asperities and gives optimum surfaces after which a lower harder durable coating is best. So, a dual coating is required. WC/C on CrN is available but not always successful delamination problems. Therefore, engines are often operated with no piston ring coating or a single durable coating which is not optimum. Work by SwRI developed a durable low friction Ti-Si-C-N coating. In a full vehicle fuel economy savings of 0.82% were obtained. The Ti-Si-C-N coating is ‘tuneable’ during the deposition process giving a softer top layer. Being the same coating with different hardness applied in one process removes delamination concerns. Coatings were tested in a tribometer and liner surfaces analysed (3D & SEM) to find the best coating. SwRI worked with Total Seal Piston Ring to install the variable hardness piston rings in a NASCAR engine to observe improved horsepower.

    About The Speakers

    After working as a qualified automotive vehicle mechanic for a number of years after leaving school, Peter attended the University of Leeds where he obtained first a Bachelors degree in Automotive engineering and then a PhD in engine Tribology. Peter continued his work at the University of Leeds for a further 5 years as a Royal Academy of Engineering Research Fellow before moving to SwRI to establish the tribology labs.