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Abstract

A nitrided layer is formed on a piston ring and a hard film is formed by arc ion plating on the nitrided layer at the outer circumferential surface. The hard film has a crystal structure comprised of mixed phases of CrN and TiN, and contains oxygen in a solid solution state in the CrN and TiN crystals. The hard film comprises chromium of 40 to 75 percent by weight, titanium of 10 to 40 percent by weight, oxygen of 0.5 to 15 percent by weight, and the remainder of nitrogen. The crystal particle size is within 1 .mu.m. The Vickers hardness of the hard film is in a range of 1300 to 2300. The crystals of CrN and TiN have a preferred orientation of (200) surface or preferred orientation of (111) surface parallel to a surface being covered, and has a columnar structure developing in a columnar shape from the base material toward the film surface. Carbon in a solid solution state may be contained instead of oxygen, and both oxygen and carbon may be contained in a solid solution state. An under film of CrN may be formed between the nitrided layer and the hard film.

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