Abstract
The formation of white etching cracks (WECs) is a dominant failure mode in wind turbine gearbox bearings that can significantly shorten their operating life. Although the phenomenon of WECs has been communicated in the field for more than a decade, the driving mechanisms are still debated, and the impact of proposed mitigation techniques is not quantified. Leading hypotheses to inhibit the formation of WECs center on material solutions, including the use of steel with high levels of retained austenite (RA). The present work aims to explore the impact of RA on the formation of WECs within AISI 8620 steel under boundary lubrication. A three ring-on-roller benchtop test rig was used to replicate WECs in samples with different levels of RA. While varying levels of RA had a minimal effect on time until failure, a significant effect on crack morphology was observed. Additionally, potential underlying mechanisms of White Etching Area formation were elucidated. Under the current test conditions, the microstructural alterations adjacent to the cracks in the lower RA samples were more developed compared to those of the higher RA samples. Additionally, the WEC networks in the high RA samples contained significantly more crack branches than those of the low RA samples.
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Acknowledgements
The authors would like to thank Dr. Maria De La Cinta Lorenzo Martin for her assistance with electron microscopy and Dr. Oyelayo Ajayi for his helpful discussion on metallurgy. Present study is a part of Project funded by John Deere Product Engineering Center in Waterloo, Iowa and Iowa State University. This work was also supported by the US Department of Energy Office of Energy Efficiency and Renewable Energy, Wind Energy Technology Office under Contract No. DE-AC02-06CH11357. The authors are grateful to DOE Project Managers Mr. Michael Derby and Mr. Brad Ring for their support and encouragement. Use of the Center for Nanoscale Materials an Office of Science User Facility was supported by the US Department of Energy Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-06CH11357.
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Roy, S., Gould, B., Zhou, Y. et al. Effect of Retained Austenite on White Etching Crack Behavior of Carburized AISI 8620 Steel Under Boundary Lubrication. Tribol Lett 67, 40 (2019). https://doi.org/10.1007/s11249-019-1153-z
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DOI: https://doi.org/10.1007/s11249-019-1153-z