Piston ring and method of manufacture

A method of manufacturing a piston ring comprising:

• providing a split annular body having an exterior surface that includes an upper surface, a lower surface, an inner circumferential surface, and an outer circumferential surface extending between the upper and lower surfaces;
• exposing the split annular body to a nitrogen-containing atmosphere for a sufficient time to produce a nitrided layer along the exterior surface of the body;
• depositing a chromium interlayer on the outer circumferential surface of the annular body;
• and
• depositing a tribological coating including a base layer, an intermediate layer overlying the base layer and a top layer overlying the intermediate layer on the outer circumferential surface of the annular body over the chromium interlayer,
• wherein:
• the tribological coating is deposited on the outer circumferential surface of the annular body by a physical vapor deposition process,
• at least one process parameter of the physical vapor deposition process is modified partway through deposition of the tribological coating such that the top layer of the tribological coating exhibits a relatively high porosity and a relatively low Vickers hardness, as compared to that of the underlying base layer, and
• the physical vapor deposition process comprises three subsequent steps, namely:
• i) a first step which comprises the deposition of the base layer on the entire outer circumferential surface of the piston ring and provides substantially uniform thickness ranging from 10 μm to 30 μm;
• ii) a second step which comprises the deposition of the intermediate layer only on a first half of the outer circumferential surface of the piston ring and provides variable thickness from 270° towards 360° and from 90° towards 0° so that the ends of the piston ring have a thickness ranging from 10 μm to 80 μm;
• and
• iii) a third step which comprises the deposition of the top layer on the entire outer circumferential surface of the piston ring and provides substantially uniform thickness of at least 5 μm.

A method of manufacturing a piston ring comprising:

• providing a split annular body having an exterior surface that includes an upper surface, a lower surface, an inner circumferential surface, and an outer circumferential surface extending between the upper and lower surfaces;
• exposing the split annular body to a nitrogen-containing atmosphere for a sufficient time to produce a nitrided layer along the exterior surface of the body;
• depositing a chromium interlayer on the outer circumferential surface of the annular body;
• and
• depositing a tribological coating including a base layer, an intermediate layer overlying the base layer and a top layer overlying the intermediate layer on the outer circumferential surface of the annular body over the chromium interlayer,
• wherein:
• the tribological coating is deposited on the outer circumferential surface of the annular body by a physical vapor deposition process,
• at least one process parameter of the physical vapor deposition process is modified partway through deposition of the tribological coating such that the top layer of the tribological coating exhibits a relatively high porosity and a relatively low Vickers hardness, as compared to that of the underlying base layer, and
• the physical vapor deposition process comprises four subsequent steps, namely:
• i) a first step which comprises the deposition of the base layer on the entire outer circumferential surface of the piston ring and provides substantially uniform thickness ranging from 10 μm to 30 μm;
• ii) a second step which comprises the deposition of the intermediate layer on the entire outer circumferential surface of the piston ring and provides substantially uniform thickness up to 10 μm;
• iii) a third step which comprises the deposition of the intermediate layer only on a first half of the outer circumferential surface of the piston ring and provides variable thickness from 270° towards 360° and from 90° towards 0° so that the ends of the piston ring have a thickness ranging from 10 μm to 80 μm;
• and
• iv) a fourth step which comprises the deposition of the top layer on the entire outer circumferential surface of the piston ring and provides substantially uniform thickness of at least 5 μm.