Abstract <p>The issues of formation of the third body during dry friction on steel of nanostructured zirconium dioxide crystals partially stabilized by yttrium oxide are considered. The assumption is substantiated that the tribological properties of the friction pair under study are determined by the properties of the films formed on the surface of the crystals. The results of electron microscopic studies of crystal friction surfaces are presented. The elemental composition has been determined, and the phase composition of the transfer films of various areas of the friction surface of crystals have been calculated. It has been established that at high magnifications, the structure of the films on the friction surface of samples with 2–4 mol% Y₂O₃ is quite uniform with traces of the boundaries of smaller particles of the transferred material. The destruction of the friction surface of the sample with a Y₂O₃ content of 8 mol% occurs at a deeper level and affects not only the layer of secondary structures, but also the underlying layers of the base material. Recommendations for the selection of friction pairs for high-temperature friction units are formulated.</p>