CORROSION AND WEAR-RESISTANCE OF SOME NOVEL AND CURRENT DIESEL EXHAUST VALVE MATERIALS

This paper summarizes the work undertaken in a five year collaborative project aimed at developing improved materials and coatings for exhau st valves in diesel engines for marine service, operating on residual fuel oils. Eighty candidate materials were assessed using a range of l aboratory tests designed to simulate various aspects of engine conditi ons. Of particular interest to this paper are those relating to high t emperature corrosion and corrosive wear in this disel engine environme nt. Following these laboratory tests, prototype engine valves were pro udced in 15 different combinations of the most promising materials and their performance was compared in severe engine trials with that of t he best currently used commercial materials. Some experimental nickel alloys, coatings and hardfacings showed considerable promise together with a cheaper, coated iron-based valve alloy. In addition to, and as a result of, these material evaluation programmes a life prediction mo del has been devised which gives engine valve lives as a function of a lloy composition and valve seat operating temperature for engines oper ating on residual fuels oils.