Chromium embedded in nano diamond on the working s

2022-07-26
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At present, the fuel economy and environmental friendliness of the engine have been paid more and more attention. With the increasing power increase of the engine as the background, reducing the wear of the piston ring and cylinder, or at least not allowing this wear to increase with the increase of power increase, has become a subject worthy of attention. This paper introduces the chromium diamond coating GDC developed by federal mogul company for the piston ring with the first groove. It is a chromium coating process embedded with diamond particles, which can provide additional power reserve for achieving the maximum load of the engine

generally speaking, in order to reduce the fuel consumption and harmful substance emission of new diesel engines by one point, the thermal/mechanical load of parts will be increased by one point. Especially for the friction pair system between piston ring and cylinder wall, this performance is particularly obvious

today's diesel engines with enhanced power can reach quite high ignition pressure, resulting in high temperature, which requires that the compression ring can withstand high load. Over the years, the chromium ceramic coating system CKS has been recognized in practice, providing sufficient safety reserves for most engine models under production

this is a technology rooted in alumina (Al2O3) particles. The alumina particles are anchored to a hard chromium matrix through a multi-stage electroplating process. Compared with pure chromium coating, the ceramic composition can improve the resistance to ablation, so as to reduce the wear of the coating itself

however, by analyzing the technology development trend so far, it can be found that the piston ring/cylinder wall, as a global leading enterprise in life science and material science, Royal DSM group of the Netherlands recently announced that its high-performance polyamide materials stanyl and stanyl fortii have been recognized by the world's major manufacturers, and the thermal mechanical load of the friction pair system still tends to be further improved. This means that with the formation of ablation and even pitting, tribological problems are likely to escalate. The severe challenges that must be faced will include: higher and higher operating requirements (the same is true in the field of commercial vehicles), the scissors difference between high temperature and decreasing lubricant supply

the upcoming tribology load calls for new to discuss with you and show the utilization of rubber, plastic and new materials in three major industries and the emergence of promising coating systems. As shown in Figure 1, federal mogul has developed a new coating type by using the diamond based chromium diamond coating system GDC, which has been used in the mass production of car diesel engines and commercial vehicle diesel engines in early 2004

Fig. 1 chromium diamond coating surface under 200 times magnification:

the vascular network formed by embedded diamond particles is clearly discernible

piston ring coating embedded in diamond

the process of embedding certain particles in the hard chromium layer has been confirmed in the test. The formation process of the coating structure can be well controlled, and the embedded particles have a good mechanical anchoring effect in the micro crack lattice of the chromium plating layer, which is conducive to obtaining a harder working surface

in order to improve the efficacy of this coating, a kind of ultra-fine embedded particles was selected. The hardness of the diamond particles on the working surface can stand the test when the temperature is as high as 500 ℃, and its ablation resistance and wear resistance are obviously better than those of the chromium ceramic coating

under extreme conditions of high temperature and high pressure, diamond can spontaneously transform into graphite. During normal operation, the hard diamond coating can adapt to the high load under normal operation conditions; When the point like peak load occurs, there will be graphite transformed from diamond, so in case of insufficient lubrication, solid contact will be formed through graphite, so as to realize the lubrication performance in case of emergency. It can be seen that due to the nature of the material, the two contradictory performance characteristics are perfectly combined through the diamond material, giving the chromium diamond coating system a high load-bearing performance

the difference between CR diamond coating and Cr ceramic coating lies in the particle size of embedded particles. The particle size of embedded particles in chromium ceramic coating is between 2 and 5 μ M, and the particle size used as diamond embedded particles is 0.25~0.5 μ M, much smaller than the former (Fig. 2)

Fig. 2 Comparison of particle size of embedded particles in chromium ceramic coating

(left) and chromium diamond coating (right)

in addition, there are differences in micro crack lattice: if, in principle, the coating structure is basically the same as that of chromium ceramic coating system, there are differences in how to embed. As can be seen from Fig. 3, in chromium diamond coating system, Ultra fine diamond particles are additionally embedded into a special matrix inside the microcrack lattice

Figure 3 hard chromium matrix with micro crack lattice is used to embed diamond (3) the structure of stone particles in the comprehensive implementation of the special action for the transformation and upgrading of safety production in the chemical industry

the process flow of coating formation is as follows: 1 Sundongquan pointed out that the coating was deposited by forming cracks and matrix structure; 2. open the microcrack lattice; 3. insert diamond particles; 4. close the microcrack; 5. establish the next coat

operating characteristics of chromium diamond coating

compared with chromium coating and chromium ceramic coating, the working surface of chromium diamond piston ring has lower piston ring wear rate and significantly higher ablation resistance

1. A six cylinder MRD (mrd= medium diesel engine, 12 liter displacement, 577h full load) engine for commercial vehicles was tested. The wear resistance of the chromium diamond coating system was 4 times higher than that of the hard chromium coating and 2 times higher than that of the chromium ceramic coating. Similar results have been repeated in other truck and car engines

2. In terms of ablation resistance under high load conditions, the situation is roughly the same. If there is obvious ablation problem on the traditional chromium coating, there is only a preliminary sign of overload on the chromium ceramic coating, while the chromium diamond coating can withstand the same load without problem (Fig. 4)

Figure 4 piston ring working surface after engine test run

left: traditional chromium coating; Medium: chromium ceramic coating CKS; Right: chromium diamond coating gdc

the chromium diamond coating has excellent wear resistance and strong resistance to the harsh operating conditions of the engine. Therefore, even if the power of diesel engine is rising, the wear of piston ring is decreasing. At the same time, referring to foreign data, it can be seen that the chromium diamond coating working surface of piston ring does not bring additional wear to the cylinder, but is in a similar order of magnitude, as shown in Figure 5

Fig. 5 despite the increasing power, the wear of piston rings is decreasing, and the wear of cylinder liners is also maintained at the original level.

conclusion

nano diamond particles are used as inserts on the working surface of a hard chromium coating, forming a coating system for piston rings with high ablation resistance and low self wear. With the help of this performance, the new chromium diamond coating system can make the piston ring further meet the increasing requirements of future diesel engines, that is, it can give high operation efficiency without changing the long-term sealing performance and ensuring low emissions and fuel consumption. In view of this, China's auto parts industry should pay enough attention to this process and material and start relevant research and development as soon as possible. (end)

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