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The exhaust valve system of combustion engines experiences a very complex contact situation of frequent impact involving micro sliding, high and varying temperatures, complex exhaust gas chemistry and possible particulates. The wear rate has to be extremely low, and the individual wearing events operate at a scale that is very demanding to detect. The tribological conditions in the exhaust valve system are expected to become even worse for engines that will follow the future emission regulations. The regulations demand reduced amounts of soot and particles, sulfur compounds, etc., which today act beneficial for the seating surfaces. The reductions are expected to increase the metal-to-metal contact.