| 摘要 |
A piston ring 1 has a diamond-like carbon film (4) formed in a thickness of 0.5 to 30 micrometers over an under film (3) on the upper and lower surfaces. The under film (3) is directly formed on the surfaces, or formed on a hard surface treatment layer consisting of a gas nitrided layer (2) or a chromium plating film (5). The diamond-like carbon is configured with any one of an amorphous carbon structure, an amorphous carbon structure having partly a diamond structure, or an amorphous carbon structure having partly a graphite structure. The under film (3) is comprised of one of more elements selected from the group consisting of silicon, titanium, tungsten, chromium, molybdenum, niobium and vanadium in an atomic content of 70 percent or more and below 100 percent, and the remaining content consisting of carbon, or one or more of said elements in an atomic content of 100 percent. The films (3), (4) may also be formed in the same way on the outer circumferential surface of the piston ring (1).
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