Plasma Electrolytic Nitriding Technology On Piston Ring Surface In Solution

An electrolyte was prepared by using formamide as penetrant and NH4Cl as conductive salt. Piston rings were treated with plasma electrolytic nitriding technology in the electrolyte through working as cathode while a stainless steel rod serving as anode. The structure, element distribution and phase composition of the modified layer on the surface of the treated piston ring were analyzed, and the effects of process parameters such as working voltage, processing time and frequency on the hardness and tribological properties of the modified layer were investigated as well. The results show that the plasma electrolytic nitriding treatment on the surface of the piston ring under the organic electrolyte system will infiltrate N and C elements simultaneously, while the main element is nitrogen. The PEN modified layer on the surface of the piston ring is composed of compound layer, diffusion layer and transition layer. The content of the N element in the modified layer gradually decreases from the surface to the inside. The main phase compositions of the PEN modified layer are iron nitrides such as Fe2-3N, Fe4N and iron carbide Fe3C. The maximum hardness of the modified layer can reach 3 times which compared to the hardness of the substrate, and it increases with the increase of working voltage, processing time and the decline of the frequency. Furthermore, friction tests show that the friction coefficient of piston ring samples will increase after PEN treatment. However, increasing of wear rate which caused by the rise of friction coefficient can be weakened by improving the surface hardness and oil storage capacity of the piston ring through choosing appropriate process parameters such as working voltage, processing time, and frequency.