Tape-casting And Activated Sintering Of W-Cu Graded Composite Materials

W-Cu composite materials and graded composite materials combining with the advantages of tungsten and copper possess excellent electrical and thermal conductivity as well as high hardness,strength,wear resistance,thermal stability,facilitating its application in the national defense industry,electronics industry,and aerospace.Presently,W-Cu functional graded composite materials have been reported,but it is still challenging to simplify forming process,sintering treatments and components adjustment.Therefore,it is difficult to prepare high-performance W-Cu graded composite material.In this work,based on the W-Cu system composite materials and graded composite materials,the rheological properties of W-Cu slurry were investigated.Meanwhile,W-Cu green tapes were also prepared.Then,compact W-Cu homogeneous composite materials and graded composite materials were prepared via binder-removal and hot-pressing sintering process.Also,the structures,properties and effect of Co on performance of W-Cu composite materials were characterized and tested.The W-Cu slurry exhibited moderate visc\osity and good stability when the binder content is 4wt.%and the solid content is 60wt.%.W-Cu green tapes with different compositions were prepared under the slurry formation.The maximum temperature of binder removal process was 800°C,at which the W-Cu composite powders with homogenously distribution were obtained.W-Cu composite materials with compact structure were prepared under the sintering condition of 900°C-200MPa-2h.With increasing of Cu content,Vickers hardness and bending strength of the W-Cu composite materials became lower,and thermal expansion coefficient and electrical conductivity became higher.Compared with W-Cu composite materials prepared via other methods,W-Cu composite materials prepared by tape-casting method have higher Vickers hardness and lower electrical conductivity,while the bending strength and thermal expansion coefficient were almost same.This consequence results from the enhanced mechanical strength of the W-Cu composite materials prepared by tape-casting method due to the existence of WC and W₂C,while,the introduction of impurity phases deteriorates the electrical conductivity.Co/W-Cu composite materials prepared at 900°C-200MPa-2h possess compact structure and excellent performance.Densification of Co/W-Cu composite materials can be attributed to the Co addition,which reacted with W and enhanced the diffusion of W through the interface of W-Cu,strengthening the interfacial bond strength and accelerating the solid phase sintering of W-Cu composite materials.Compared with W-Cu composite materials,Co/W-Cu composite materials have higher Vickers hardness,lower electrical conductivity and thermal expansion coefficient,as well as similar bending strength.Those results can be attributed to the sintering process and the enhanced interfacial bonding strength by Co addition,while damage the network of Cu and deteriorate the electrical conductivity.Finally,according to designed component distribution of the W-Cu graded composites,seven layers Co/W-Cu graded composite material with 40-100wt%Cu was prepared.Also,its structure and morphology were characterized.The results showed that the density of the as-prepared W-Cu graded composite material is high.Besides,its parallelism between layers was good without any obvious defects.Meanwhile,the components exhibited a graded variety trend along with the thickness direction,and the content distribution maintained uniform in each layer,no obvious aggregation could be found in the studied W-Cu graded composites.