Contact fatigue performance of helical gears with surface coatings

The objective of this study was to evaluate the performance of helical gears with applied surface coatings either with or without Inorganic Fullerence Like Material (IFLM) nano-particles. The contact fatigue performance of case-carburised and tempered S156 steel helical gears coated with Balinit C1000, Balinit C*, CrN + IFLM, C6 + IFLM and Nb–S coatings were tested using a 91.5 mm centre distance back-to-back test rig. The constant torque, constant speed contact fatigue tests were carried out for up to 50 million cycles to evaluate the performance of the different coatings in comparison with the uncoated, as-ground condition. The endurance contact fatigue tests were conducted at two different contact stress levels with the performance assessed against the extent of micro-pitting damage and the associated average gear tooth profile deviation. It has been found that gears coated with Balinit C showed the lowest micro-pitting damage followed by those with C6 + IFLM and Nb–S coatings. The Nb–S coated gears showed the lowest gear profile deviation followed by those coated with Balinit C. Other coatings tested resulted in large gear tooth profile deviations below the pitch diameter. From the results of gear testing, it is concluded that the Nb–S coated gears showed the best overall contact fatigue performance, followed by Balinit C coated gears that gave minimum micro-pitting damage and low levels of gear tooth profile deviation.