Chromium nitride ion-plating coating and its production method, as well as piston ring used for internal combustion engine
[Task] The chromium nitride ion-plating coating has a property that it is hard but is liable to peel off. Year by year, the required level of wear resistance and scuffing resistance becomes higher in a diesel engine. The property of a coating is improved to enhance the wear resistance and scuffing resistance and also to improve resistance against peeling off. [Means for Solution] (1) Composition is mainly composed of chromium, nitrogen, and carbon, and the concentration of carbon relative to the total concentration of the main components is from 4 to 8% by weight. (2) The crystal structure is that texture of the CrN (111) plane orientation is from 0.4 to 2.0 in terms of a CrN (111) structural coefficient. (3) Vickers hardness is from Hv 1600 to Hv 2000.
1. A chromium nitride ion-plating coating wherein the fracture surface of the coating has columnar crystals extending toward the surface of the coating, characterized in that the coating comprises chromium, nitrogen, and carbon; the concentration of carbon relative to the total concentration of the chromium, nitrogen, and carbon is from 4 to 8% by weight; the crystal structure of the coating is mainly formed of CrN-type chromium nitride; the texture of the CrN (111) plane orientation is from 0.4 to 2.0 in terms of a CrN (111) structural coefficient; and further a Vickers hardness is from Hv 1600 to Hv 2000.
2. A piston ring of an internal combustion engine, characterized in that the chromium nitride coating according to claim 1 is formed on at least an outer peripheral surface of the piston ring.
3. A method for forming a chromium nitride ion-plating coating according to claim 1 , wherein a metallic chromium coating is formed by an arc ion-plating, and, subsequently, a chromium nitride ion-plating coating is formed by an ion-plating method in a low-pressure gas atmosphere consisting of nitrogen gas, hydrocarbon gas, and argon gas at a bias voltage of −30V to 0V.