THE IMPROVEMENT OF MICROMECHANICAL PROPERTIES AND WEAR RESISTANCE OF CHROME-NICKEL LASER COATING USING THE FINISHING FRICTION TREATMENT
Chrome-nickel coatings applied on the parts surfaces using laser clad deposit are characterized by the significant surface undulation and roughness. The friction treatment of deposited surfaces used as the finishing operation allows preventing the demerits of customary grinding (burns, microcracks, dangerous tension stresses) and ensuring additional improvement of durability and wear resistance, favorable compressing stresses formation and fine finish. In this research, the authors used both the microhardness testing by regenerated indents method and the method of kinetic micro-indentation for the study of strength and plastic properties of NiCrBSi laser coating, processed by friction treatment using the hemispherical sliding indenter made of finely dispersed cubic boron nitride (borazon). The authors considered the coating wear mechanisms in the conditions of slide rubbing friction resulting from the micromechanical properties of strengthened layer. Using the research of microhardness distribution in depth of the processed by friction treatment surface layer, the authors determined the maximum strengthening in thin layer (the thickness is 5-7 µm) with greatly dispersed structure on the coating surface. It is determined that the surface friction treatment, comparing with the electrolytic brightening, not only improves the surface quality (reduces its undulation) but also increases (according to the micro-indentation data) the possibility of surface layer to resist to mechanical contact action. As a consequence of micromechanical properties improvement, the friction treatment in the conditions of sliding friction without lubricants causes the change of basic wear mechanisms - from seizure and plastic edging to the prevailing elastic edging. It causes the elimination of burn-in period and the relevant decrease of the strengthened coating wear intensity at the initial stage of friction.