The use of selective plasma nitriding on piston rings for performance improvement

Abstract

Plasma nitriding process was used in this work for surface treatment of gasoline engine piston rings. The research was conducted to optimise metallurgical properties and to improve the manufacturing route of the rings. The results are compared to the conventional gas nitriding process. Selective nitriding of thin wall gasoline piston rings is very important because the side surfaces are deleterious to the engine performance. Plasma nitriding proved that selective nitriding is possible using a simple mounting system, leading to homogeneous properties on both inner and outer diameter surfaces. Only a diffusion zone, without grain boundaries nitrides, composes the nitrided microstructure. The surface hardness is increased up to 1100 HV0.1. The mechanical tests showed that the performance of selective plasma nitrided rings is superior to the gas nitrided counterpart. The wear rate is 30% higher for the plasma nitrided rings, but acceptable for practical purposes.