Materials Characterization 123 (2017) 349–353 Contents lists available at ScienceDirect Materials Characterization journal homepage: www.elsevier.com/locate/matchar Atomic scale characterization of white etching area and its adjacent matrix in a martensitic 100Cr6 bearing steel Y.J. Li a, b, * , M. Herbig a ,S.Goto a ,D.Raabe a, ** a Max-Planck Institut für Eisenforschung, Max-Planck-Str. 1, Düsseldorf D-40237, Germany b Center for Interface-Dominated High Performance Materials, Ruhr-Universität Bochum, Bochum 44780, Germany ARTICLE INFO Article history: Received 25 June 2016 Received in revised form 8 November 2016 Accepted 2 December 2016 Available online 5 December 2016 Keywords: Severe plastic deformation Grain boundary segregation Carbide dissolution Nanocrystalline structure Rolling contact fatigue ABSTRACT Atom probe tomography was employed to characterize the microstructure and C distribution in the white etching area (WEA) of a martensitic 100Cr6 bearing steel subjected to rolling contact fatigue. Different from its surrounding matrix where a plate-like martensitic structure prevails, the WEA exhibits equiaxed grains withauniformgrainsizeofabout10nm.SignificantCgrainboundaryenrichment(>7.5at.%)andanoverall higher C concentration than the nominal value are observed in the WEA. These results suggest that the formation of WEA results from severe local plastic deformation that causes dissolution of carbides and the redistribution of C. © 2016 Elsevier Inc. All rights reserved. 1. Introduction The white etching area (WEA) phenomenon is known as a microstructural feature formed upon rolling contact fatigue of bear- ingcomponents [1] andrailways [2] thatlimitstheirservicelife [3,4]. WEAs usually form in bearings in a depth of several 100 l m beneath the contact surface and is normally observed together with white etching cracks (WECs) [3]. The term ‘white etching’ stems from the homogeneous white appearance of these regions in optical micro- graphs after polishing and Nital etching. Although substantial efforts have been made to study WEAs/WECs, their detailed formation mechanisms are still unclear and remain the subject of intense research [1,3,5-8]. Microscopy analyses of WEAs by transmission electron microscopy (TEM) [3,9-11], scanning electron microscopy (SEM) [3,10,11], and atom probe tomography (APT) [12] reveal that WEAs consist of nanocrystalline grains with grain sizes varying between 10 and 300 nm. However, other TEM results indicate that some portion of the WEAs might be amorphous [9]. There is also a discrepancy concerning the presence of carbides in WEAs. Some sourcesreportthatWEAsarefreeofcarbides [10,13],whereasothers * Correspondence to: Y.J. Li, Max-Planck Institut für Eisenforschung, Max-Planck- Str. 1, Düsseldorf D-40237, Germany. ** Corresponding author. E-mail addresses: y.li@mpie.de, yujiao.li@rub.de (Y. Li), d.raabe@mpie.de (D. Raabe). suggest that cementite particles with a size of several nanometers existintheWEA [12],yet,withoutgivingdetailsabouttheirlocation and composition. APT provides a unique combination of high spatial resolution and chemical sensitivity and has been shown to be a powerful tool for the analysis of complex materials, such as multicomponent and nanocrystallinematerialsinvolvingprecipitation,carbidedissolution and segregation [14–16]. Different from our previous study which focused on the near-surface (200 nm below the contact surface) region of an axial thrust bearing [17], here APT was employed to investigate the subsurface (about 200 l m below the contact surface) microstructure and the distribution of the main alloying element C in both, a WEA and its adjacent matrix in a martensitic bearing steel subjected to rolling contact fatigue (RCF). We aim at identifying the keymicrostructuralfeaturesofWEAsincomparisonwithitsadjacent matrixanditsformationmechanismbasedonaquantitativeanalysis of the C distribution in three dimensions at the atomic scale. 2. Experimental Methods The material studied in this work was a through-hardened martensitic 100Cr6 steel tempered at 150 ◦ C. RCF test was carried out to create WEAs/WECs (see [17] for details concerning RCF test conditions). Fig. 1 (a) displays the circumferential cross section of the damaged bearing washer, where a dark etching area (DEA) and http://dx.doi.org/10.1016/j.matchar.2016.12.002 1044-5803/© 2016 Elsevier Inc. All rights reserved.