Tribofilm formation and mild wear by tribo-sintering of nanometer-sized oxide particles on rubbing steel surfaces

The present study is the first to show that the supply of nanometer-sized particles of Fe2O3, SnO2, CuO, or Bi2O3 oxide on rubbing steel surfaces induces transition to mild wear with sliding distance, and that the wear transition behavior depends on the type of supplied oxide. The mild wear is due to formation of the wear-protective tribofilm on the rubbing surfaces, and observations confirm that the tribofilms are produced by tribo-sintering of the supplied oxide particles. The mild wear transition behavior is explained by the sintering rate of the supplied oxide particles, which is related to the oxygen diffusion coefficient in the oxide and the particle diameter. When the supplied oxide is of high diffusivity, the tribofilm formation rate is high, owing to the high sintering rate of the oxide particles, and the mild wear transition occurs at a short sliding distance. In the case of Fe2O3 oxide, the sliding distance of the transition from severe to mild wear is decreased when finer particles are supplied, suggesting that fine particles are easily sintered on the wear surface.