Tribo-mechanical etching of structural ceramic materials during lubricated severe sliding contact

An unusual phenomenon has been observed in the contact area on the surfaces of three structural ceramic materials that were subjected to severe lubricated sliding contact with hardened steel. Silicon carbide, alumina, and partially stabilized zirconia (PSZ) were slid against a carburized 4620 steel ring in a block-on-ring test rig lubricated with polyalphaolefin synthetic oil. A step-loading protocol was used for the scuffing test. At the conclusion of the tests, the outline of grains and phases in the contact area of the ceramic materials was clearly visible, as if the surface had been etched. This behavior, what we have termed “tribo-mechanical etching,” is attributed to different mechanisms, including anisotropic mechanical and thermal deformation of each grain (SiC and Al2O3) and the phases (PSZ) in the ceramic material during severe sliding contact. Because of the hexagonal close-packed (hcp) crystal structure of the SiC and Al2O3 grains, they exhibit anisotropic mechanical and thermal behavior. Another possible mechanism for revealing the grain outlines includes uneven/unequal transfer of metal into different ceramic grains as a result of differences in the surface energy of each grain.