A piston has a piston main body including an aluminum alloy, and a covering layer formed on the outer surface of the piston main body, and the covering layer has a first plating layer including an iron-phosphorous alloy, and a second plating layer including a nickel-phosphorous alloy formed on the first plating layer.

A piston has a piston main body including an aluminum alloy, and a covering layer formed on the outer surface of the piston main body, and the covering layer has a first plating layer including an iron-phosphorous alloy, and a second plating layer including a nickel-phosphorous alloy formed on the first plating layer.

A piston ring including a base coating, for example a chromium-based material with an intentionally etched crack network is provided. The cracks of the base coating are filled with a sliding material, which is expected to improve scuff resistance. The sliding material includes polyamideimide (PAI) and Fe.sub.2O.sub.3. The sliding material can also include solid lubricant and hard materials. Alternatively, the base coating is formed of diamond-like carbon and applied to the piston ring by physical vapor deposition (PVD). In this case, the base coating includes protuberances or bumps, and the sliding material is disposed between protuberances of the base coating.

A piston ring including a base coating, for example a chromium-based material with an intentionally etched crack network is provided. The cracks of the base coating are filled with a sliding material, which is expected to improve scuff resistance. The sliding material includes polyamideimide (PAI) and Fe.sub.2O.sub.3. The sliding material can also include solid lubricant and hard materials. Alternatively, the base coating is formed of diamond-like carbon and applied to the piston ring by physical vapor deposition (PVD). In this case, the base coating includes protuberances or bumps, and the sliding material is disposed between protuberances of the base coating.

The present disclosure is a combination of a cylinder and a piston ring, the combination including a cylinder of an internal combustion engine and a piston ring sliding on an inner peripheral surface of the cylinder. The piston ring has an outer peripheral surface sliding on the inner peripheral surface of the cylinder, and the outer peripheral surface is formed of a substantially hydrogen-free amorphous carbon coating. The Vickers hardness Hd of the amorphous carbon coating and the Vickers hardness Hb of the inner peripheral surface of the cylinder satisfy Hd+Hb≤2500 HV. The ratio ID/IG of the peak intensity of the D band to the peak intensity of the G band in a Raman spectrum obtained by measuring the amorphous carbon coating by Raman spectroscopy is 0.60 or more and 1.33 or less.

The present disclosure is a combination of a cylinder and a piston ring, the combination including a cylinder of an internal combustion engine and a piston ring sliding on an inner peripheral surface of the cylinder. The piston ring has an outer peripheral surface sliding on the inner peripheral surface of the cylinder, and the outer peripheral surface is formed of a substantially hydrogen-free amorphous carbon coating. The Vickers hardness Hd of the amorphous carbon coating and the Vickers hardness Hb of the inner peripheral surface of the cylinder satisfy Hd+Hb≤2500 HV. The ratio ID/IG of the peak intensity of the D band to the peak intensity of the G band in a Raman spectrum obtained by measuring the amorphous carbon coating by Raman spectroscopy is 0.60 or more and 1.33 or less.

To provide a long-life compression ring without an increase in the outer peripheral abrasion near the gap regardless of the ring material or the presence or absence of the outer peripheral hard coating, in an annular compression ring having a pair of gap faces opposed to each other to form a free gap and a nominal diameter d1 equal to an inner diameter of a cylinder to which the compression ring is attached to along with a piston, a self tangential force is 5 N to 50 N, and a radius of curvature R1 and the nominal diameter d1 satisfy a relationship:

−0.01≤(2R1−d1)/d1<0.002

where the radius of curvature R1 is that of outer peripheral arcs of gap end portions in a free shape state before the compression ring is attached to the cylinder, and the gap end portions are defined in ranges between the gap faces and positions where a center angle from a midpoint of the free gap is 35°.

To provide a long-life compression ring without an increase in the outer peripheral abrasion near the gap regardless of the ring material or the presence or absence of the outer peripheral hard coating, in an annular compression ring having a pair of gap faces opposed to each other to form a free gap and a nominal diameter d1 equal to an inner diameter of a cylinder to which the compression ring is attached to along with a piston, a self tangential force is 5 N to 50 N, and a radius of curvature R1 and the nominal diameter d1 satisfy a relationship:

−0.01≤(2R1−d1)/d1<0.002

where the radius of curvature R1 is that of outer peripheral arcs of gap end portions in a free shape state before the compression ring is attached to the cylinder, and the gap end portions are defined in ranges between the gap faces and positions where a center angle from a midpoint of the free gap is 35°.

To provide a sliding member, such as a piston ring for an internal combustion engine, having low friction and excellent toughness. The above-described problem is solved by a sliding member (10) such as a piston ring coated with a Cr—B—Ti—V—(Mn, Mo)—N-based alloy film (2) on a sliding surface (11) thereof, and configured so that the alloy film (2) contains one or both of Mn and Mo and has a total content of the Mn and the Mo within a range of 2 mass % or less. Preferably, a B content is within a range of 0.1 mass % to 1.5 mass %, inclusive, a V content is within a range of 0.05 mass % to 1 mass %, inclusive, and a Ti content is within a range of 0.05 mass % to 1.5 mass %, inclusive.

To provide a sliding member, such as a piston ring for an internal combustion engine, having low friction and excellent toughness. The above-described problem is solved by a sliding member (10) such as a piston ring coated with a Cr—B—Ti—V—(Mn, Mo)—N-based alloy film (2) on a sliding surface (11) thereof, and configured so that the alloy film (2) contains one or both of Mn and Mo and has a total content of the Mn and the Mo within a range of 2 mass % or less. Preferably, a B content is within a range of 0.1 mass % to 1.5 mass %, inclusive, a V content is within a range of 0.05 mass % to 1 mass %, inclusive, and a Ti content is within a range of 0.05 mass % to 1.5 mass %, inclusive.