Investigation On Fabrication,microstructure And Properties Of W_sf/W-Cu Composites

With the increase of the capacity of the high-voltage transmission grid,and the improvement of automation level and the sensitivity degree for the low-voltage transmission and control systems,the W-Cu contact materials should have more excellent properties.Considering that the tungsten fiber is an ideal reinforcement for amorphous materials,high temperature materials and refractory metals due to its excellent characteristics.Therefore,it could be anticipated that W-Cu composites reinforced with tungsten short fibers(Wsf)would exhibit excellent mechanical properties and arc erosion resistant property.Based on this,in this paper,the influence of mixing methods for the dispersion of tungsten fibers was investigated;various W-Cu composites reinforced with tungsten short fibers(Wsf)with different contents and length-diameter ratio were prepared by high temperature sintering and infiltration method;the effects of tungsten fibers on the microstructure,density,hardness,electrical conductivity,tensile strength,arc erosion resistance,friction and wear properties of the composites were studied;the parameters of electroless plating and magnetron sputtering on the surface of tungsten fibers were investigated,and the influence of the coatings on the interface bonding state were also discussed.The main conclusions are as follows:(1)The dispersion of tungsten fibers can be achieved by wet mixture in glycerol and anhydrous ethanol with the volume ratio of 2:1.The dispersion degree of tungsten fibers by drying mixture lies in 3.95%-5.44%.The densities of the W-Cu composites reinforced with 4 mm length fibers are generally high,and the density reaches to be 14.66g/cm3 at fiber content of 4%.When the fiber lengths are 1 mm and 2 mm,the density and hardness of the composites increase with the increase of fiber content.(2)With the increase of the content of tungsten fibers,the contiguity of the W-Cu matrix would be destroyed and result in a decrease of electrical conductivity.The tensile strength increased with the increase of the fiber length.Compared with the traditional W-Cu composite,the maximum tensile strength increased by 4.4%,7.9%and 13.7%respectively when the fiber length is 1mm,2mm and 4mm.The tensile fracture characteristics include the ductile tearing of copper matrix,transgranular fracture of tungsten particles,as well as the interface de-bonding and extraction,fracture of tungsten fibers.(3)The W-Cu composites reinforced with tungsten short fibers exhibited better improved arc erosion resistance.When the fiber length is 4 mm,the breakdown strength of the composites increased and then decreased with the increase of the fiber content.The maximum breakdown strength was 6.4119×107V/m.The friction coefficient increased first and then decreased.When the content of tungsten fibers was 2%,the friction coefficient increased to be 0.604.The wear mechanisms include abrasive wear,adhesive wear and slight oxidative wear.(4)The electroless nickel plating and magnetron sputtering process can deposit a layer of nickel coating on the surface of the fiber.The nickel layer can optimize the interface bonding so the hardness increases while the electrical conductivity decreases.Temperature of 90?,pH of 9 and 2 minutes is chosen for electroless plating.For the magnetron sputtering,the suitable parameters include power of 20 W,sputtering time of 60 min,sputtering pressure of 2 Pa and vacuum degree of 2×10-4 Pa.(5)For the W-Cu composite reinforced with Ni-plated tungsten fibers,the arc erosion area decreased and the breakdown strength increased.The tensile strength also increased.When the fiber content was 0.5%,the W-Cu composites reinforced with Ni-plated and un-plated tungsten fibers,exhibited improved tensile strengths by 10.48MPa and 23.72MPa respectively,due to the metallurgical bonding state.The wear mechanisms included abrasive wear,adhesive wear and slight oxidation wear.