Simulation of Tribological Performance of Coatings for Automotive Piston Ring and Timing Chain in Bench Testing

Piston rings with three different coatings were tested on a lubricated cylinder liner for friction force, wear depth, electric contact resistance (ECR) and acoustic emission (AE), using Micro-Tribometer model UMT. UMT was also used to test four types of coatings on timing chain linkage pins to evaluate their scratch resistance with a wedge-shaped micro-blade made of tungsten carbide. Scratch resistance measurements with a diamond stylus of 0.5 μm radius were much less distinctive for the four coatings, as compared to those with the micro-blade. It was found that when the micro-blade broke through the coating on the linkage pins, the AE signal changed more rapidly than the friction force. The friction force could not distinguish tribology performance between Coating 1 and Coating 2, whereas the AE easily differentiated the two coatings. In the testing of piston-ring coatings, it was found that ECR increased with running time during the first half hour or so. It reflected the lubricant buildup at the interface, since the lubricant introduces a much higher electrical resistance. The AE signal was found not always correlated with friction forces, since mechanical interactions contributing to AE are not only along the factional direction. Good correlation was found for wear depth measured in-situ using UMT and post-test using a Tencor profilometer. Testing repeatability was demonstrated.