Investigation of wear surfaces in Si+-implanted uni-directionally aligned silicon nitride using TEM and XPS

Uni-directionally aligned silicon nitride, which exhibits both high strength and high toughness, was implanted with Si+ ions at a fluence of 2×1017 ions/cm2 and an energy of 200 keV. Wear tests of the Si+-implanted material were carried out using a ‘Block-on-Ring’ wear tester under non-lubricated conditions against commercially available silicon nitride materials. The wear mechanism has been investigated by surface analyses using cross-sectional transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). TEM and XPS results revealed the presence of a silicon oxide layer on the wear resistant ion-implanted layer in the wear track of the Si+-implanted specimen, while there was no such layer on the unimplanted specimen. It is concluded that the wear product is formed by tribochemical reaction of the opponent ring test piece with the atmosphere during the wear test, and contributes to the high wear resistance of the Si+-implanted uni-directionally aligned silicon nitride.