Research On The Structure And Properties Of Silver-based Composites Reinforced By CNTs

Silver is an attractive metal in the field of materials science,because of its high thermal and electrical conductivity.Silver matrix composites are widely used in many fields such as integrated circuit,plug coater,brush and circuit breaker.Carbon nanotubes(CNTs)are considered to be excellent composites for electrical contact and circuit breaker applications due to their unique properties.Therefore,CNTs reinforced silver matrix composites are very attractive and can meet the growing demand for high performance thermal conductivity materials.In this paper,CNTs reinforced silver matrix composites were prepared by ultrasonic spray electroless plating combined with powder metallurgy,and the effects of sintering process and flake powder metallurgy on the microstructure and properties of the composites were studied.Silver nanoparticles were coated on CNTs by ultrasonic spray electroless plating,firstly.And silver matrix composite powders with different CNTs contents were prepared by solution ball-milling,and then the composite powders were prepared into block composites by discharge plasma sintering(SPS)and hot press sintering(HP),respectively.Firstly,the effect of sintering process on the microstructure and properties of composites was studied.The microstructure and mechanical properties of composite powders and composites were analyzed and tested by Raman spectroscopy,metallographic microscope,field emission scanning electron microscope,transmission electron microscope microhardness tester,eddy current conductometer and electronic universal testing machine.The results showed that the preparation process of ultrasonic spray could effectively improve the dispersion of CNTs.When the spray time was within 5 min,CNTs could be evenly distributed on the substrate of silicon wafer without obvious aggregates.The composites prepared by the sintering process of SPS showed that the dispersion of CNTs in the matrix was uniform,and the grain size was smaller,about 5?m,and the mechanical properties were significantly improved.When the volume fraction of CNTs was 2.5 %,its hardness increased to 92 HV and tensile strength to 221 Mpa.According to the theoretical calculation of strengthening mechanism,it is the grain refinement strengthening and load transfer strengthening mechanism that play the main strengthening role.Secondly,the influence of flake powder metallurgy on the properties of CNTs reinforced silver matrix composites was studied.The spherical silver matrix powder was prepared by high-energy ball-milling to obtain the flake silver powder,and silver matrix composite powder materials with different CNTs contents were prepared by solution ball-milling.Then the composite powder was prepared into block composite material by the sintering process of SPS,and its structure and properties were studied.The results showed that the dispersion of CNTs in the flaked silver-based composite powders was more uniform,and the geometric compatibility between the flaked silver-based powders and CNTs was obviously better.At the same time,the mechanical properties of the composites were also significantly improved.When the volume fraction of CNTs reached 2.5 %,its hardness was increased to 94.7 HV,and its tensile strength was increased to 246 Mpa,which was about twice that of pure silver(124 Mpa)under the same preparation process.It shows that CNTs also play an important strengthening role in composite materials.