Subsurface deformation and microcrack formation in Ti–35Nb–8Zr–5Ta–O( x) during reciprocating sliding wear

Abstract

The relationship between dry sliding reciprocating wear, subsurface deformation and microcrack formation in Ti–35Nb–8Zr–5Ta–O( x) has been investigated. Three subsurface zones: a chemically altered tribo-layer, a plastic shear zone, and a plastic deformation zone layer were identified, their depth increasing with increasing contact stress. Transmission electron microscopy showed {110} and {112} planar slip deformation throughout the plastic zones, the planar slip band spacing decreasing with decreasing distance to the reciprocating sliding wear surface. Within the plastic shear zone {110}/{110} and {110}/{112} slip band intersections were observed, their number density increasing with decreasing distance from the wear surface. These slip bands intersections were associated with localized shear displacement, the magnitude of the shear displacement increasing with increasing oxygen. Finally as the tribo-layer was approached microcrack formation at intersecting slip band was observed. Microcrack propagation proceeded along the interface of the {110} slip bands with microcrack linkage being observed as reorientation of the slip bands occurred. Ultimately a featureless surface tribo-layer containing cracks running both parallel and perpendicular to the wear was encountered. These observations are consistent with a model for debris formation that involves microcrack formation, linkage and ultimately shear type II shear delamination.