Durability of plasma-sprayed Cr₃C₂-NiCr coatings under rolling contact conditions

Abstract

The aim of this paper was to address the rolling contact fatigue (RCF) failure mechanisms of plasma-sprayed Cr3C2-NiCr coatings under different tribological conditions of contact stress. Weibull distribution plots of fatigue lives of the coated specimens at different contact stresses were obtained. The failure modes of coatings were identified on the basis of wore surface observations of the failed coatings. Results showed that the RCF failure modes can be classified into four main categories, i.e., surface abrasion, spalling, cohesive delamination, and interfacial delamination. The probabilities of the surface abrasion and spalling type failures were relatively high at low contact stress. When the coatings were subjected to abrasion and spalling type failures, the failure of the coating was depended on the microstrcture of the coating. The stress concentration near the micro-defects in the coating may be the may reason for the formation of spall. The coatings were prone to fail in delamination under higher contact stresses. However, the delamination of coating may be related to distribution of shear stress amplitude within coating. The location of maximum shear stress amplitude can be used as a key parameter to predict the initiation of subsurface cracks within coating in rolling contact.

Key words： rolling contact fatigue; coating; Weibull distribution; failure mode; mechanism

Acknowledgements

The authors are grateful for the support by the National Natural Science Foundations of China (Grant Nos. 50835003 and 50805047) and Shanghai Leading academic discipline project (B503). The author X C Zhang is also grateful for the support by the Shanghai Chenguang Planning Project (2008CG36), Shanghai Rising-Star Program (08QA14023) and Doctoral Fund of Ministry of Education of China (20090074120006).

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