The application of surface coatings for low wear and low friction performance between valve train components

The UK produces >150 million tonnes of CO2 annually, a large proportion of which comes from the transport sector. The UK looks to lead the way in CO2 emission reduction, committing to an 80% reduction by 2050. Meeting this target is going to be a huge challenge for engineers in all sectors of industry, and improved component efficiency will have a large role to play. This study has looked at the three novel friction and wear reduction techniques that may find application in the valve-train component of the automotive internal combustion engine. The aim of this study has been to establish the effectiveness of a range of: i) diamond-like carbon (DLC) coatings; ii) carbon nitride (CNx) coatings, and; iii) ionic liquid based lubricants, at reducing friction and wear in the valve-train. The main focus of this work has been the study of thin, wear resistant, and lubricious DLC coatings. A range of DLC coatings have been investigated to determine their performance in an instrumented valve-train test rig and compared to coating mechanical properties. Similar work has been conducted with CNx coatings, which are also thin, wear resistant and lubricious, whilst maintaining a lower hardness to elastic modulus ratio. It has been confirmed in this work that coating adhesion, hardness and abrasion resistance are key to coating durability in the valve-train along with the novel observation that impact toughness, particularly resistance to high angle inclined impact, is a very important factor in determining coating lifetimes. Also work has also been done to investigate the lubrication properties of ionic liquids. These liquids have very different chemistry to traditional hydrocarbon based lubricants but have demonstrated values of friction coefficient similar to that of engine oil. The mechanism by which these liquids are retained in the contact and provide lubrication bears further investigation.