| 摘要 |
A piston ring comprises a martensitic stainless steel ring having a nitrided layer formed in the surface portion thereof, and a titanium nitride film coated on the outer sliding surface of the ring by an ion-plating process. According to a first embodiment of the present invention, the titanium nitride film has a nitrogen concentration which is gradually increased toward the top surface thereof to gradually lower a toughness of the film toward the top surface and to make a surface portion of the film more brittle than the other portion of the film. On the other hand, according to a second embodiment of the present invention, the titanium nitride film has a nitrogen concentration which is gradually decreased toward the top surface and to make a surface hardness of the film HV 1800 or less.
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