Abstract
This study carried out experimental rolling contact fatigue (RCF) tests on two types of materials: commercially available Cr-Mo alloy steel and 1.55% Ni-doped Cr-Mo alloy steel, using a twin-disc test rig. Micropitting was identified as the most prominent damage feature on the rolled surfaces of the disc samples during the gears' RCF tests. To investigate gear surface characteristics and wear behavior, RCF tests were conducted on both material types. The twin-disc test was designed to replicate asperity contact on mating gear flank surfaces, using low-speed cylindrical disc specimens and high-speed crowned disc specimens, ensuring a minimum effective contact area of 8.5 mm. After testing, surface morphology and topographical changes were examined using Scanning Electron Microscopy (SEM). The results revealed that 1.55% Ni-doped Cr-Mo alloy steel demonstrated superior resistance to contact fatigue failure compared to the commercially available Cr-Mo alloy steel, as evidenced by a lower micropitted area ratio, shallower pitted depth, and fewer pits. Specifically, the Ni-doped alloy exhibited a 5.66% lower micropitting area ratio under the same test conditions. Furthermore, prior studies support these findings, showing that the 1.55% Ni-doped steel performs better than the 2% Ni-doped alloys. Therefore, 1.55% Ni-doped Cr-Mo alloy steel is recommended for transmission gears to minimize RCF damage.