WEAR-RESISTANT COATINGS PRODUCED FROM TiN–TiB₂  AND TiN–Si₃N₄ COMPOSITES BY ELECTROSPARK DEPOSITION AND LASER TREATMENT

Abstract

The TiN–20% TiB₂ and TiN–20% Si₃N₄ nanocomposites sintered in a microwave field with a frequency of 2.45 GHz were applied to a steel substrate by electrospark deposition in the temperature range 1400–1500 °С in a nitrogen atmosphere. In deposition modes with an energy of isolated pulses in the range 0.2–0.75 J, changed surface layers consisting of a coating with a thickness of 50–90 µm and a heat-affected zone of increased hardness with a thickness of 40–60 µm on the substrate were produced. A part of samples was subjected to additional laser surface treatment to increase the density and homogeneity of the deposited layers. Substantial influence of electrospark mass transfer on the phase composition of the transferred material was established. According to XRD data, the TiN–TiB₂ composite, with all its components being present in the coating, was more stable. In the case of the TiN–Si₃N₄ composite, silicon nitride completely dissociated to form Ti₅Si₃ and Ti₂N compounds. For both compositions, iron, penetrating into the coating from the substrate, was found in the deposited layer. The TiN–TiB₂ and TiN–Si₃N₄ coatings had a hardness of 14–15 GPa and 11–12 GPa, respectively. Comparative tribotechnical tests of the coatings with a spherical VK6 hardmetal counterface in quasistatic and dynamic modes revealed that electrospark deposition of the TiN–TiB₂ composite combined with subsequent laser treatment was highly efficient. In tribotechnical tests, the linear wear of this coating was 0.5 µm, corresponding to a twelvefold increase in the wear resistance as compared to that of the TiN–Si₃N₄ coating for the dynamic friction test. The deposition of the TiN–Si₃N₄ composite enabled a double increase in the wear resistance of the substrate in the dynamic testing mode. In this case, additional laser treatment of the coating turned out to be inefficient.