Preparation and properties of new self-lubricant YBa₂Cu₃O₇/Cu composites

YBa₂Cu₃O₇ (YBCO) powder was prepared by oxalate co-precipitation method. YBCO/Cu composites with different mass fractions were prepared by vacuum hot-pressed sintering method. The density, hardness and conductivity of YBCO/Cu composites were measured. The friction and wear test was performed on YBCO/Cu composites by MMU-5GA abrasion equipment. The microstructure, wear surface morphology and phase composition of YBCO powder and YBCO/Cu composites were characterized by the means of XRD, SEM and TEM. The influence of YBCO mass fraction on microstructures and properties of YBCO/Cu composites were investigated. The results indicate that the YBCO powder phase is Y123 phase with apparent layer structure, and powders are nano-scale particles with high purity and less impurity. The matrix structures of YBCO/Cu composites are obviously refined and the tribological performance are improved by adding YBCO nano-particles. With the increase of YBCO mass fraction, the uniformity of YBCO nano-particles in matrix reduces and particles agglomerates gradually, the conductivity and density of YBCO/Cu composites decrease, the hardness firstly increases then decreases, the friction coefficient gradually reduces. The friction and wear performance of 3% YBCO/Cu composite are best. The strength mechanisms of YBCO/Cu composites are Orowan strengthening, thermal mismatch strengthening and grain refinement strengthening.The dominant wear mechanisms are plastic deformation wear, abrasive wear and fatigue flaking.