Effect of as-ground surface and the BALINIT® C and Nb–S coatings on contact fatigue damage in gears

The influence of as-ground surface and the BALINIT® C and Nb–S coatings on contact fatigue damage have been investigated using testing of case-carburised S156 steel helical gears. The micro-surface features on the as-ground gear flank tend to initiate micro-pitting. In BALINIT® C coated gears, the surface irregularities are removed by polishing effect resulting in small scale initiation of micro-pitting at the interface between polished and unpolished regions. In Nb–S coated gears, the coating tends to penetrate and fill-up the surface micro-valleys and hence showed only scattered micro-pitting. The Nb–S coated gears did not produce any tooth profile loss whilst the BALINIT® C coated gears produced profile loss. However, both BALINIT® C and Nb–S coated gears show enhanced contact fatigue performance.