Tribological behaviour of uni-directionally aligned silicon nitride against steel

Textured silicon nitride, where the β-Si 3N 4 grains were uni-directionally aligned, was fabricated and the effect of anisotropy in microstructure on tribological properties was investigated, compared with a conventional Si 3N 4. The wear tests were carried out for the tribopair of textured silicon nitride ceramic and steel using a block-on-ring tester without lubrication. For the textured Si 3N 4, tribological properties were evaluated in three directions with respect to the grain alignment; the plane normal to the grain alignment and in the directions parallel and perpendicular to the grain alignment in the side plane. The friction coefficient values of each specimen were of the same level under the same sliding conditions. The values of specific wear rate for the plane normal to the grain alignment were lower than those of the other specimens for all sliding conditions. It is considered that the high wear resistance of this plane was caused by restricted microfracture, such as grain dropping and minimal abrasion by wear debris. Both the friction coefficient and specific wear rate were decreased with increasing sliding speed and normal load because of the formation of lubricative FeO between the sliding surfaces.