Investigating the corrosion-fatigue wear on CrN coated piston rings from laboratory wear tests and field trial studies

The interacting mechanisms of corrosion and fatigue wear of the CrN coated piston rings were investigated in two ways: (1) by comparing the laboratory test data to field results, and (2) by simulating the stress distribution and crack origins in the CrN coating using a Finite Element Method (FEM). The surface and interface characterizations confirmed that fatigue wear resulted in cracking and spalling of the CrN coating. At the same time, corrosive wear was promoted by sulfur incursion along boundary defects in the CrN coating. FEM simulations showed that the magnitude of stresses at the interface of Cr particle/CrN matrix was a function of Cr particulate sizes, and they also identified crack initiation sites at rubbing contacts. The dominant factors contributing to the propagation of the surface/subsurface cracking were elucidated. Inherent defects initiated cracks, and the repetitive shear stress coupled with the effects of corrosive species gave rise to an acceleration of crack enlargement and subsequent severe spalling of the CrN coating.