Excellent Seizure and Friction Properties Achieved with a Combination of an a-C:H:Si DLC-Coated Journal and an Aluminum Alloy Plain Bearing

Friction occurring between the crank journal and main bearings accounts for a large share of the mechanical losses of automotive engines. The effects of higher in-cylinder pressures and narrower bearings have raised the specific load applied to bearings, making it essential to secure sufficient seizure resistance as well. For the purpose of meeting both requirements, we have endeavored to reduce friction and improve seizure resistance by applying a diamond-like carbon (DLC) coating to the crank journal. In the present study, a bearing tester was used that has received international standard certification from the International Organization for Standardization for reproducing the sliding behavior occurring between the crank journal and main bearings in actual engines. Test results indicated that a silicon-containing hydrogenated amorphous carbon (a-C:H:Si) DLC-coated journal showed a definite friction reduction and a marked improvement in seizure resistance. An acoustic emission (AE) analysis revealed that an adhesion-induced AE peak observed for a steel journal was not seen for the DLC-coated journal. Additionally, tin and aluminum elements in the bearing material that were transferred to and observed on the sliding surface of the steel journal were not seen on the DLC-coated journal. Accordingly, the low affinity of the DLC coating with these metal elements presumably led to the clear friction reduction and superior seizure resistance displayed by the DLC coating.