TRIBOLOGICAL PROPERTIES OF AG/BSCCO SELF-LUBRICATING COMPOSITES

The superconductors Bi₂Sr₂CaCu₂O_x (Bi2212 ) and Ag/Bi2212 composites samples were prepared by the powder metallurgy method. The frictional behaviors of Bi2212 pins in contact with stainless steel plate were examined from -196 to 20°C on friction and wear tester. When the temperature was lower than the superconducting transition temperature, the friction coefficient of Bi2212 dropped sharply, and it kept 0.11 with increase of the test time. The microstructure and morphology of Ag/Bi2212 composites were investigated by means of X-ray diffraction (XRD), transmission electronic microscope (TEM) and high resolution transmission electronic microscope (HRTEM). The elemental compositions of the worn surfaces of Ag/Bi2212 composites were determined by using energy dispersive X-ray analysis (EDXA). The results showed that the superconducting structure of Bi2212 was not changed and Ag was distributed in the Bi2212 matrix. Ag doping improved the toughness of oxide ceramics Bi2212. The friction test results of Ag/Bi2212 composites showed the tribological properties were improved at room temperature. The friction coefficient of 10%Ag/Bi2212 against stainless steel showed a lower value (0.2) and the wear rate of 15%Ag/Bi2212 was minimum (9.5×10^-5 mm³·(N·m)^-1 ). The lubrication of soft metallic film and load of hard matrix were the mechanism of decreased friction and anti-wear of Ag/Bi2212 composites.