A method for producing a piston ring for a cylinder that moves in a sliding direction includes providing a piston ring base material having an upper surface, a lower surface and an outer circumferential surface having a first recess between the upper surface and the lower surface, forming a hard film in the first recess and on a cylindrical surface at a predetermined thickness, and removing, by performing a polishing process on the sliding surface, the hard film formed on the cylindrical surface and a part of the piston ring base material disposed adjacent to the removed hard film, to form a second recess. The second recess is formed by removing an area of the removed part of the piston ring base material as a result of polishing the sliding surface due to a difference in the hardness of the hard film and the piston ring base material.

A method for producing a piston ring for a cylinder that moves in a sliding direction includes providing a piston ring base material having an upper surface, a lower surface and an outer circumferential surface having a first recess between the upper surface and the lower surface, forming a hard film in the first recess and on a cylindrical surface at a predetermined thickness, and removing, by performing a polishing process on the sliding surface, the hard film formed on the cylindrical surface and a part of the piston ring base material disposed adjacent to the removed hard film, to form a second recess. The second recess is formed by removing an area of the removed part of the piston ring base material as a result of polishing the sliding surface due to a difference in the hardness of the hard film and the piston ring base material.

A piston ring may include a stainless steel base having between 8% and 15% by weight of chromium, together with other elements and impurities, and having a hardness between 350 HV and 420 HV. The piston ring may also include a superficial nitrided layer having a depth of no more than 60 μm and an average hardness measured upon the surface exceeding 800 HV. The nitrided layer may include a plurality of nitride particles, which may have a maximum size of 5 μm and may be distributed over between 4% and 8% of an area of the nitrided layer.

A piston ring may include a stainless steel base having between 8% and 15% by weight of chromium, together with other elements and impurities, and having a hardness between 350 HV and 420 HV. The piston ring may also include a superficial nitrided layer having a depth of no more than 60 μm and an average hardness measured upon the surface exceeding 800 HV. The nitrided layer may include a plurality of nitride particles, which may have a maximum size of 5 μm and may be distributed over between 4% and 8% of an area of the nitrided layer.

A process for obtaining a piston ring may include providing a piston ring of an internal combustion engine and submitting a surface of the piston ring to a laser surface heat treatment. The surface may be a sliding surface of the piston ring. The piston ring may be a one piece piston ring and/or a scrapper ring.

A process for obtaining a piston ring may include providing a piston ring of an internal combustion engine and submitting a surface of the piston ring to a laser surface heat treatment. The surface may be a sliding surface of the piston ring. The piston ring may be a one piece piston ring and/or a scrapper ring.

The present disclosure provides a sealing ring assembly having a first ring and a second ring, configured to seal a high-pressure region from a lower pressure region of a piston and cylinder device. Accordingly, the sealing ring assembly includes a high-pressure boundary and a low-pressure boundary. Each ring may be segmented, and the first and second rings interface along a surface. Along the surface at the interface, a groove open to the lower pressure region aids in pressure locking the sealing ring assembly. A pocket in the second ring allows for high pressure gas to aid in balancing radial forces on the sealing ring assembly. As the sealing ring wears, the first and second rings remain engaged with one another.

The purpose of the invention is to provide technology, which, in addition to being capable of forming thick hard carbon films of excellent durability even using PVD, is able to establish both chipping resistance and wear resistance in the formed hard carbon film and able to improve low friction properties and peeling resistance. Provided is a coating film to be coated on the surface of a substrate, the coating film having a total film thickness of greater than 1 μm to 50 μm wherein: when a cross-section is observed using bright field TEM images, white hard carbon layers that are shown as relatively white and black hard carbon layers that are shown as black are alternately laminated in the thickness direction; and the white hard carbon layers have regions that have grown in a fan-shape in the thickness direction.

The purpose of the invention is to provide technology, which, in addition to being capable of forming thick hard carbon films of excellent durability even using PVD, is able to establish both chipping resistance and wear resistance in the formed hard carbon film and able to improve low friction properties and peeling resistance. Provided is a coating film to be coated on the surface of a substrate, the coating film having a total film thickness of greater than 1 μm to 50 μm wherein: when a cross-section is observed using bright field TEM images, white hard carbon layers that are shown as relatively white and black hard carbon layers that are shown as black are alternately laminated in the thickness direction; and the white hard carbon layers have regions that have grown in a fan-shape in the thickness direction.

A sliding member includes a carbon transfer layer and can superiorly effectively decrease friction and reduce wear. A method produces the sliding member. The sliding member includes a substrate and a carbon transfer layer. The carbon transfer layer is disposed on the surface of the substrate and includes both sp.sup.2 bonded carbon and sp.sup.3 bonded carbon. The carbon transfer layer preferably has a ratio sp.sup.3/(sp.sup.2+sp.sup.3) of the sp.sup.3 bonded carbon to the totality of the sp.sup.2 bonded carbon and the sp.sup.3 bonded carbon of 0.1 or more.