Teikoku Piston Ring Co., Ltd.

Teiko Piston Ring Co., Ltd.

Toshiaki Imai

Akira Harayama

A piston ring is formed with a nitrided layer over all surfaces and formed with a composite chromium plating film over the nitrided layer in the outer circumferential surface. The composite chromium plating film has a network of cracks formed on the outer surface and interior. Spherical alumina particles are fixed in these cracks. The average size of the spherical alumina particles is 0.7 to 10 .mu.m and the dispersion ratio of the spherical alumina particles is 3 to 15 percent by volume.

Composite chromium plating film and sliding member covered thereof

A piston ring formed with a nitrided layer over all surfaces and formed with a composite chromium plating film over the nitrided layer in the outer circumferential surface. The composite chromium plating film has a network of cracks formed on the outer surface and interior. Si.sub.3 N.sub.4 particles are fixed in these cracks. The average size of the Si.sub.3 N.sub.4 particles is 0.8 to 3 .mu.m and the dispersion ratio of the Si.sub.3 N.sub.4 particles is 3 to 15 percent by volume.

An outer circumferential surface of a piston ring is covered with a physical vapor deposition film, chemical vapor deposition film or composite chromium plating film. The physical vapor deposition film or chemical vapor deposition film consists of chromium or titanium nitrides (for instance CrN, Cr.sub.2 N, a mixture of Cr and Cr.sub.2 N, TiN) or carbides (for instance CrC, TiC). The composite chromium plating film contains carbides (for instance SiC) or nitrides (for instance Si.sub.3 N.sub.4) or oxides (for instance Al.sub.2 O.sub.3) in cracks in the film. A cylinder liner is made of spheroidal graphite cast iron.

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Okaya, Japan

Toshiaki Imai