Abstract: Using an arc ion plating apparatus, a metal not capable of forming a carbide or nitride, such as cobalt, nickel or molybdenum is set as a first target, a metal capable of forming a carbide or nitride, such as silicon, titanium, vanadium, chromium, iron, zirconium, niobium or tungsten is set as a second target and nitrogen, acetylene or methane is fed as a process gas to form a film on a piston ring body which is an article to be coated, thereby providing a piston ring comprising a hard film formed on at least its sliding outer face of the piston ring body, said hard film comprising a mixed structure formed of the metal not capable of forming a carbide or nitride and a carbide or nitride of the metal capable of forming a carbide or nitride. In this piston ring, the hard film has so good adhesion to the body material or film toughness that no cracking or film separation tend to occur even when the film is formed in a large thickness.

Abstract: An under coating 2 and a hard film 3 are formed on the outer circumferential surface of a piston ring 1 by an ion plating process. The under coating 2 is composed of at least one of Cr, Cr.sub.2 N, and CrN. The hard film 3 is composed of a hard coating material containing 3 percent to 20 percent by weight of oxygen in a solid solution state in a crystal structure of CrN and having the Vickers hardness of 1600 to 2200.

Abstract: Each side rail of a combined oil ring, which includes a spacer-expander and two side rails, has an ion nitriding treatment layer on an outer peripheral surface of the rail. The inner peripheral surface of each rail may either be a bare surface or have either a soft surface treatment or a hard chrome plating. The upper and lower surfaces of the rail may either be a bare surface or have a soft surface treatment. The method comprises coiling a strip to form a coil, placing the coil on a jig so that only the outer peripheral surface is exposed to the ion nitriding and then cutting the coil to form the individual rails with a gap.

Abstract: A hard film 2 is applied to cover an outer circumferential surface of a piston ring 1 by an ion plating process. Either 3 percent to 20 percent by weight of oxygen, or 2 percent to 11 percent by weight of carbon is included in a solid solution state in a crystal structure of CrN in the hard film 2. The Vickers hardness of the hard film 2 is in a range of 1600 to 2200.