Tribofilm Formation by Tribo-Sintering of Nanometer-Sized Particles

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When nanometer-sized particles, which have high surface energy, are artificially supplied on rubbing surfaces, wear-protective tribofilms are formed on the surfaces. The previous study has demonstrated that the supply of nanoparticles of an oxide of high diffusion rate, such as Fe_2O_3, SnO_2, CuO, or Bi_2O_3, induced transition to mild wear with sliding distance. The mild wear was due to the formation of the wear-protective tribofilms on the rubbing steel surfaces, and observations confirmed that the tribofilms were produced by tribo-sintering of the supplied oxide particles. Therefore, it is expected that the tribofilms produced by the supply of nanoparticles reduce wear even if no particles exist on the surfaces.The purpose of this project is to study wear behavior of the tribofilms produced by the supply of nanoparticles on the steel surfaces. Particularly, the influences of the type and size of supplied particles on the wear of the produced tribofilms have been investigated in detail.Tribofilms were produced in air or vacuum(8x10^<-4> Pa) by using a pin-on-disc wear machine. The pin and disc specimen material is normalized 0.45 mass% carbon steel. The supplied particles were CuO(mean particle diameter : 48nm), Fe_2O_3(30nm), SnO_2(21nm) or Bi_2O_3(51nm) oxide in the case of air atmosphere, and Cu(50nm, 1μm) in the case of vacuum atmosphere.It was found that the tribofilms produced by the supply of nanoparticles on the rubbing surfaces reduced the wear considerably, depending on the type of the supplied particles. Particularly the sliding distance of the mild wear transition was the longest for the tribofilms by the supply of Bi_2O_3 oxide particles, resulting in low total wear volume.