Study On Mo/Cu-Al₂O₃Electrical Contact Materials

Mo/Cu-Al₂O₃composites combine both the high electronic conductivity andthermal conductivity and the good ductility of Cu, and the high strength and hardness,the low coefficient of thermal expansion of Mo. Therefore, they are widely used aselectronic contactors, spot welding electrode, electronic packaging materials and heatdissipation materials, etc. Recently, Mo/Cu-Al₂O₃are studied by more and morepeople as vacuum switch electrical contacts, they will be one of the more useful newfunctional materials with the best properties and the lowest cost.Mo/Cu-Al₂O₃composites have been prepared by vacuum hot-pressed oxidationsintering with different content of Mo in this paper. The preparation technology andbase properties of the composites are studied, and the hot deformation of thecomposites is emphasized. Meanwhile, the constitutive equations of the Mo/Cu-Al₂O₃were established. The processing maps of the composites were established based ondynamic materials model in order to serve for the thermal processing formulation. Inthe meantime, the friction and wear behaviors of Mo/Cu-Al₂O₃composites in thepresence of electric currents of various intensities were examined. The worn surfacemorphologies were observed, and the wear mechanisms were discussed, too.The parameters of the material preparation technology are followed as: thesintering temperature,950°C; the compaction pressure,30MPa; the vacuum degree,1.5×10^-2Pa; and the time, two hours. The microstructures of the10%Mo/Cu-Al₂O₃,20%Mo/Cu-Al₂O₃, and30%Mo/Cu-Al₂O₃composites are well distributed, and thedensity of the materials are very high. The microhardness and electric conductivitywere measured, and the microstructures were observed. At the same time, thedensification mechanism was accounted briefly. The results show that the densificationway is gained almost by particles rearrangement, plastic deformation and grainsslipping. The Mo and Al₂O₃oxidation particles enhance the body strength of theMo/Cu-Al₂O₃composites. The relative density, microhardness and electricalconductivity of the10%Mo/Cu-Al₂O₃,20%Mo/Cu-Al₂O₃,30%Mo/Cu-Al₂O₃ composites are98.2%,99.3%,96.9%,120HV,140HV,154HV,48.8%IACS,46.1%IACS,43.9%IACS, respectively.The Mo-Cu composites were compressed unidirectionally using the Gleeble-1500D thermal simulator. The true stress-strain curves of the10%Mo/Cu-Al₂O₃,20%Mo/Cu-Al₂O₃, and30%Mo/Cu-Al₂O₃composites were also investigated. Theresults show that the dynamic recrystallization occurred almost the whole way in thehot deformation; the effect of strain ratio and temperature are an important factor ofthe dynamic recrystallization. The Mo particles are available for the formation ofrecrystallization core on their surface, and the dynamic recrystallization temperature ofthe composites decreases, too. Meanwhile, the relative constitutive equations of theMo/Cu-Al₂O₃composites were worked out based on the relation among the flow stress,deformation temperature and strain ratio. And the processing maps of the Mo/Cu-Al₂O₃composites were drawn, too. Therefore, the optimal thermal processingtechnology of the materials is made according to the microstructure and dynamicmaterials model.The study of friction and wear behaviors of three Mo/Cu-Al₂O₃compositesexperiment was done in the HST-100current-carrying high speed friction and weartester. And also observed the microstructure of the surface and sub-surface. The resultsshow that the wear rate and friction coefficient of Mo/Cu-Al₂O₃composites increasedwith increasing electric current and load. The oxidation hard phase and ablation pitappeared on the worn surface. The most wear forms are abrasive wear, adhesive wearand electric wear.