Phase transformation in white etching area in rolling contact fatigue

Abstract

Abstract. Rolling contact fatigue (RCF) involves microstructural change in the subsurface of contact. The changed microstructure is generally termed as white etching area (WEA) as it appears white under optical microscope when etching in nital solution. WEA has been acknowledged as one of the primary failure modes in RCF since it causes severe local inhomogeneity of microstructure. It was reported that WEA consists of nano ferrites as martensite grains and carbides are significantly refined in the WEA. Some carbides are dissolved. In some cases, an amorphous-like structure was occasionally observed in the WEA, indicating that phase transformation may possibly occur. The WEAs were studied by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Electron back scattered diffraction (EBSD). The result showed that WEA is dominated with an amorphous phase with martensite, austenite and carbides embedded interior. A distinct interface between the matrix and the WEA was present. In addition to grain refinement down to nanometers, phase transformation including amorphization and austenitization happened in WEAs. The content of austenite was increased from 2% in the matrix to 20% in the WEA. The analysis showed that phase transformation is controlled by plastic deformation mechanism.

Further understanding of rolling contact fatigue in rolling element bearings - A review

“…Consists of a structure of fine material [171] or equiaxed fine nano-crystalline ferrite grains 10-100 nm in diameter and is free of large carbides [86,90,172,173]. There also appears to be an amorphous phase with nano-martensite and austenite [174].WEA exhibits no preferential crystallographic orientation [173]. Formation Mechanism Carbon partitions from WEB into adjacent DER to become trapped at dislocations or precipitates as layers of cementite [165].…”