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An observation on the initiation of micro-pitting damage in as-ground and coated gears during contact fatigue

Lookup NU author(s): Dr Moorthy Vaidhianathasamy, Professor Brian Shaw


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The effect of surface features on as-ground gears and the influence of BALINIT (R) C and Nb-S coatings on the initiation of micro-pitting damage have been examined in case-carburised and tempered S156 steel helical gears subjected to contact fatigue using back-to-back gear testing. The initiation of micro-pitting damage has been studied using scanning electron and optical microscopy examination. It has been observed that micro-cracks tend to initiate against the sliding direction preferentially from microvalleys on the surface of as-ground gears, particularly when the depth of micro-valley is favourably oriented at an angle against the sliding direction. It has been found that the micro-pitting damage is drastically reduced in both coated gears. In BALINIT (R) C coated gears, the micro-scale surface irregularities are removed by a wear process resulting in a polished surface of the gear flank below the pitch diameter which is attributed to the effect of hard BALINIT (R) C coating. However, there is region of interface between the polished and unpolished regions of gear flank where there is small scale initiation of micro-pitting due to the absence of BALINIT (R) C coating at micro-valleys. In Nb-S coated gears, the coating tends to penetrate and fill-up the micro-valleys on as-ground surface modifying the gear flank surface. Hence, the micro-pits tend to initiate only at some micro-valley sites where the Nb-S coating is locally removed during running. This study shows that, both BALINIT (R) C and Nb-S coated gears show enhanced resistance to micro-pitting damage by removing localised stress concentration at micro-valleys present on as-ground gears. (C) 2012 Elsevier B.V. All rights reserved.

Publication metadata

Author(s): Moorthy V; Shaw BA

Publication type: Article

Publication status: Published

Journal: Wear

Year: 2013

Volume: 297

Issue: 1-2

Pages: 878-884

Print publication date: 15/01/2013

ISSN (print): 0043-1648

ISSN (electronic): 1873-2577

Publisher: Elsevier Science


DOI: 10.1016/j.wear.2012.11.001


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Funder referenceFunder name
FP6-515840European Commission (FOREMOST project)