Narrow Results

We report on the effects of using various doping 3d, 4d and 5d transition metal elements on the stability of the supersaturated FCC Ag–Cu solid solution prepared by mechanical alloying. We find that the addition of W does not have any influence on the stability of the Ag–Cu solid solution. Moderate effects are observed for Ru, Fe and Co, while the addition of Ni partially destabilizes the Ag–Cu solid solution. The results are discussed in the framework of kinetic and thermodynamic processes.

Spark plasma sintering (SPS) is employed to fabricate self-lubricating Al₂O₃-SrSO₄ nanocomposites incorporated with and without Ag addition. The friction and wear properties have been evaluated using a high temperature friction and wear tester from room temperature to 600°C in dry sliding against alumina ball. X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) analyzer were used to investigate microstructure and self-lubrication mechanisms of nanocomposites after wear tests at different temperatures. Al₂O₃-SrSO₄ nanocomposites with optimum compositional combinations exhibit low and stable friction coefficients of 0.22 and wear rates in the order of 10^-5 mm³/Nm at high temperatures. At low temperature, the Ag additives in the composite form a discontinuous lubricating film to effectively reduce friction and wear. With increasing test temperature, plastic deformation of SrSO₄ during sliding plays an important role in formation of lubricating films on worn surfaces to reduce the friction and wear.

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.

The viscosity of the eight binary systems (Cu–X ($\mathrm{\text{X}}=\mathrm{\text{Ag}}$, Al, Sn, Mg) system and Ag–X ($\mathrm{\text{X}}=\mathrm{\text{Sn}}$, Sb, In, Au)) was re-assessed, employing a new CALPHAD-type equation model proposed in our previous work. The calculated viscosities of the binary alloys were compared with the experimental data. It was found that this CALPHAD-type equation is very effective in fitting with the experimental data. Therefore, this work proves the validity of our new CALPHAD-type equation model for accurate viscosity predictions in alloys with varying component compositions.