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Research leading to analytical modelling of surface pitting failure in contacts similar to those in spur and helical gears is reported. Development of this model is based on observations of surface pitting morphology, analysis of crack initiation and propagation for a single or a set of distributed cracks. The morphological experiments on a geared roller fatigue tester revealed slow growing surface cracks followed by a rapid growth of a single crack leading to a pit. Near surface inclusion is found to be the cause of this rapid growth. Models for determining the life for developing a single surface crack and for propagating this crack to form a single deep pit are also described.

High-rate-reactively-sputtered (HRRS) hard coatings have been deposited on steel rollers. The effects of substrate hardness and coating hardness on the tribological behavior of titanium nitride (TiN) coated steel rollers have been investigated with a roller-on-roller tribo-tester. The properties of both the substrate and the coating were found to be very important in determining the wear performance of the rollers. From experimental results it was noted that the relatively hard TiN coatings enhanced the scuffing-failure-load by ten times when deposited onto relatively hard substrates (Rc 62), but did not improve the performance of soft substrates (Rc 45). For a relatively soft substrate (Rc 45), the benefit of using the relatively soft TiN coating rather than the hard TiN coating has been demonstrated.