Dislocation behavior and cracking mechanisms at the WC-Co cemented carbide surface under dry sliding conditions

Abstract

The deformation processes and strain transfer mechanisms within the tungsten carbide (WC) and cobalt (Co) components at the surface significantly influence the tribological performance of cemented carbides. Nevertheless, the mechanisms governing plastic deformation and the initiation and spallation of cracks under frictional stresses in cemented carbides are obscure. This study employed focused ion beam (FIB) micromachining techniques to fabricate transmission electron microscopy (TEM) lamellae from the tribolayer, which arises during the dry sliding of cemented carbides. The microstructural response and dislocation slip systems within the tribolayer were subsequently scrutinized using TEM under two-beam conditions and transmission Kikuchi diffraction (TKD). Moreover, friction-induced atomic displacements were delineated and the strain transfer mechanisms were elucidated using molecular dynamics (MD) simulations. The results indicated that dislocations primarily slipped on prismatic $\left(01\overline{1}0\right)$ or pyramidal$\left(01\overline{1}1\right)$ planes, with the angular relationship between the orientation of the WC grain and sliding direction determining the specific slip plane and the $\left(a\right)(b=1/3\left(11\overline{2}0\right)$) dislocations being primarily activated. The initiation of intragranular cracks in WC was closely linked to the motion of $\left(a\right)$ dislocations on the pyramidal planes. However, intercrystalline cracks typically originate and propagate along the basal planes $\left(0001\right)$ at high-angle grain boundaries. This study provides a theoretical foundation for designing wear-resistant cemented carbides characterized by exceptional subsurface elastoplastic adaptability.