Piston rings have a wide variety of materials and different properties. The selection of piston ring material should consider its service conditions, performance requirements, ring type and other factors. Generally speaking, the piston ring material of internal combustion engine shall meet the following requirements:
1. High enough mechanical strength at high temperature
2. Wear resistance and low friction coefficient
3. It is not easy to produce adhesion and easy to run in
4. The processing is convenient and the price is cheap
In this way, the piston ring material is required to have certain strength, hardness, elasticity, wear resistance (including oil storage), corrosion resistance, thermal stability and processability. At present, the material of piston ring is mainly cast iron. With the strengthening of engine, there is a trend of transition from gray cast iron to malleable cast iron, nodular cast iron and steel. See table 2-1 for common materials and properties.
Table 2-1 common materials and properties of piston rings

However, today's introduction is not the piston ring of common materials, but the metal ceramic composite film piston ring (ceramic infiltrated piston ring or ceramic metal piston ring for short), hereinafter referred to as metal ceramic piston ring.
Cermet piston rings are made by infiltrating boron nitride (part of cubic boron nitride) ceramics with * self-lubricating function into the surface layer of piston ring friction pair at low temperature (below 200 ℃) by using the world's * advanced "plasma chemical vapor deposition technology", so that the working surface layer of piston rings is ceramic. The piston rings after ceramic infiltration have good wear resistance, wear resistance and corrosion resistance, Therefore, the service life of the piston ring can be improved. The composite ceramic is infiltrated into the surface of piston ring by plasma chemical vapor deposition, which is different from the ceramic spraying process on the surface of other piston rings. This process method can make the composite ceramic material have a firm bonding force with the surface of piston ring without cracking and falling off.  

In addition, the cermet composite layer has an electronic structure similar to rhodium, so it can carry out Combustion Catalysis in the engine and greatly reduce the emission content of CO and HC. Therefore, ceramic impregnated piston rings also have catalytic effect.
 "Cermet composite film" technology passed the * appraisal in 1997.
Ceramic impregnated piston rings have been widely used in major engine plants with good application effect.  
It forms "functional ceramics" compounded with metals, which has the outstanding characteristics of high surface hardness, low friction coefficient, wear reduction and long service life.
At low temperature (below 200 ℃), nitride (composite ceramic material) is infiltrated into the tool surface by plasma chemical vapor deposition.
Features:
1. Low temperature growth. When the film-forming temperature is below 200 ℃, it will not damage the substrate and surface of the workpiece, nor deform the workpiece, and will not affect the machining accuracy and assembly performance.
2. The connection is firm. Because the metal diffuses with boron nitride and cubic boron nitride in the state of vacuum plasma to form dumping functionally gradient materials, the composite films will not peel off at high temperature or impact.
3. Both hardness and toughness are improved. Due to the two-phase diffusion of composite film and metal to form inclined gradient functional material, it not only plays the role of firm combination of transition layer, but also improves the bonding strength, tensile capacity and bending resistance of ceramic, and its toughness exceeds that of ceramic itself.
4. Good wear resistance at high temperature. The experimental results show that compared with chromium plating, the hardness of the composite film increases greatly with the increase of temperature in the environment of 250 ℃ - 350 ℃, and the surface hardness increases by more than hv210, while the hard chromium decreases significantly after 250 ℃, and decreases by about hv110 at 350 ℃. Thus, compared with the workpiece without composite film plating, the ceramic plated workpiece has better wear resistance in high temperature environment.
5. Strong oxidation resistance. The experimental results show that the composite film still has good oxidation resistance and acid-base resistance when the temperature is greater than 1000 ℃.
6. It has the function of oxidation and catalysis. When the ceramic penetrates into the metal surface, an appropriate amount of electron vacancy is generated, which makes the composite film have the oxidation catalytic effect on CO and HC, and greatly reduces the exhaust emission pollution of the engine.
7. Good winding and plating performance. Composite films are chemical vapor deposition, so composite films can be grown wherever gas can pass through, and the processing conditions are not limited by the shape and position of the workpiece.
8. Wide application fields. In addition to being applied to the engine, the composite film is also suitable for the friction pairs of various machines, high-temperature and corrosion-resistant parts, various cutting tools and molds, and can adapt to various metal or non-metal materials through different process parameters.