Study And Comparison Of Tribological Properties Of High Temperature Superconducting Material Bi₂Sr₂CaCu₂O_x And Composites

J.Krim et al.had studied the interface friction of Pb surface and nitrogen molecule adsorbed on it with quartz crystal microbalance(QCM) from 1986.They reported the friction force associated with electronic.The friction changing when samples under superconducting transform.The superconducting transition temperature of high temperature superconducting material Bi₂Sr₂CaCu₂O_x(132212) is above 90K, which can be realized at liquid nitrogen temperature.So this study has a strong theory and utility value to study the tribological property of high temperature superconducting material.This study was using powder metallurgy method to prepare B2212-Ag self-lubricating composite with uniform and compact structure.The microstructure was studied by XRD and SEM.Ag was doped using metal Ag powder.The mechanical properties were tested and the tribological properties were investigated in low temperature,room temperature,and in vacuum.The toughness and tribological mechanism were discussed.Various amounts of Ag additions in the microstructural evolution and related mechanical and tribological properties of B2212 were studied. The results showed:(1) The density and fracture toughness of composites increased with the increase of Ag content,and the micro-hardness decreased with the increase of Ag content, probably as a result of strengthening mechanism caused by Ag addition.Ag particles may resist crack propagation by deflecting and bridging the crack,and pinning the propagating crack tip.Furthermore,addition of Ag did not have an adverse effect on the critical current density of B2212 superconductors.(2) The friction coefficient of pure B2212 dropped abruptly when the temperature cooled below the superconducting transition temperature.In normal state the average friction coefficient was 0.25,and at liquid nitrogen temperature,the friction coefficient decreased sharply to 0.15. (3) Self-lubricating composite B2212-Ag had fine tribological property.In normal state,the tribological property of composites which prepared from Ag was best when the Ag content was 10wt.%.At vacuum,the friction coefficient decreased with the increase of Ag content,and didn't change with the sliding velocity.The friction coefficient of pure B2212 decreased with the increase of temperature at normal temperature,and the friction coefficient of composite is little influenced by temperature When B2212 was doped with Ag.