Influence of hexagonal boron nitride nanocrystals on wear processes in brass

In summary, a method for preparing of the composite anti-frictional material based on brass (containing 68.5 wt. % Cu and 31.3 wt. % Zn) has been developed. The nanocrystalline hexagonal boron nitride obtained by low-temperature chemical synthesis has been used as the friction modifier. Morphology and size of hexagonal boron nitride (h-BN) nanoparticles has been determined by broadening of the X-ray diffraction maxima. They are found to have the disc-shapes with the mean diameter of 240 nm and mean thickness of 25 nm. To obtain composite alloy brass + 1 wt. % h-BN, the chemically copper-plated h-BN nanoparticles should be directly introduced into the brass-melt. Measurements of the thermal expansion coefficient of the composite material brass + 1 wt. % h-BN showed that friction modifier insignificantly affects its value what means the stabilization of the geometry of friction pairs made from this material. Alongside with this, the increase in the room temperature thermal conductivity as compared with that of matrix indicates the possibility to intensify the heat exchange processes at the friction surfaces at high loadings in the high-temperature range of operation. This will ensure the stability of the friction pairs at high temperatures and loadings. Studying the tribological properties shows that h-BN as the friction modifier radically changes the wear mechanism. It is evidenced by changes in the morphologies and the linear sizes of the wear particles at ''catastropic'' loadings (225 N). Tribological measurements conducted at lower loadings (20 and 51 N) confirm the positive influense of h-BN on the tribological properties of this newly developed anti-frictional material. The optimal amount of friction modifier is estimated to be a few wt. % of h-BN. (author)