Silicon nitride ceramics for valve train applications in advanced diesel engines

Advanced diesel engines will require valve train components capable of operating under significantly higher pressures and temperatures than seen in current engines. Also, these materials will be subjected to a severe corrosive environment. Silicon nitride offers excellent wear resistance and corrosion resistance at high temperature and is under evaluation for these components. The stability and mechanical reliability of silicon nitride needs to be thoroughly assessed and well understood before components can be successfully implemented in valve train applications. In this paper, the mechanical and thermal properties (strength, toughness, damage tolerance, contact wear, thermal shock, and corrosion/oxidation) of commercially available silicon nitrides were investigated. The role that microstructure and second phases play in wear and damage resistance was described. Degradation of mechanical properties of silicon nitrides was discussed in conjunction with oxidation and glassy phase softening. A guideline for material selection for valve train applications was suggested.