A ROLLING-CONTACT FATIGUE STUDY OF HARD CARBON COATED M-50 STEEL

Hard carbon coatings with diamond-like properties were applied on AISI M-50 steel rods which were subjected to rolling contact fatigue (RCF) testing at a cyclic Hertzian stress level of 5.5 GPa. The coatings were produced using a single, broad beam ion source that directed 450 eV ions, derived from a methane discharge, onto the rods. Results from preliminary tests show that hard carbon coatings alter the fatigue failure characteristics of this material substantially. They caused the B50 lifetime to increase from 7.5 x 10(6) stress cycles for uncoated material to 13 x 10(6) but they also caused the B10 lifetime to decrease from 4 x 10(6) stress cycles for the uncoated material to less than 1 x 10(6). The coatings induced an order of magnitude increase in lifetime for some tests. Scanning electron microscopy, surface profilometry and microhardness tests were used to examine coating morphologies, investigate coating/base material interfaces and demonstrate hardness increases.