Other variables which influence the wear resistance and friction of coatings are listed in Table 2. Caterpillar's experience has shown that the surface finish of the coatings and the combination of the sliding pairs of materials greatly influence wear. We have used single cylinder engine tests to evaluate many ring and liner coating combinations. From this work it was concluded that a smooth surface finish on the order of 0.20-0.40 micron center line average roughness compared to 1.00 micron for a cast iron liner is necessary for good wear of the ring and liner combinations.

Interactions between the coating and the lubricant must also be considered as an important part of the coating selection process if optimum wear and friction properties are to be achieved. A lubricant should be selected which has the potential for providing adequate lubrication performance in all areas for the conditions of load, speed, temperature, and environment anticipated.

The primary role of the lubricant will be to reduce friction and wear. Particularly under boundary lubrication conditions, the degree of effectiveness for any lubricant/sliding pair is highly dependent on the chemical composition of the lubricant basestock and its additive components as well as the nature and chemical composition of the surfaces to be lubricated.

Additive response differs among most ceramics and metals depending on composition. Considering the wide variety of potential surface chemistries possible, it is not likely one optimum lubricant chemistry will be found for them all.


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