Fabrication,microstructure And Property Of W-Cu Composites With Special Structure

W-Cu composite materials have been widely used in large scale integrated circuit and high power electronic devices as heat sink materials owing to their excellent properties such as high electrical and thermal conductivity,low thermal expansion coefficient,etc.As the increase of the integration level of integrated circuits and the power of electronic devices,there have brought more strick requirements on the performance of W-Cu heat sink materials.However,it is difficult to prepare W-Cu composites with high density and homogeneous microstructure by the traditional powder metallurgy process due to the mutual insolubility and differences of density,melting point between W and Cu.In recent years,preparation of ultra-fine W-Cu composite powders and high performance W-Cu functional materials become the important parts in the developments of W-Cu materials.In this dissertation,Cu-coated W powders(W-10 wt.%Cu,W-10Cu)were synthesized by the electroless plating method and W-10 Cu composites were prepared by pressing and liquid sintering the powders.On this basis,three-layered W-Cu functionally graded materials(FGMs)were fabricated by lamination pressing the W-Cu composite powders with different W particle sizes distribution and liquid phase sintering method.The microstructure and physical and mechanical properties of the W-Cu FGMs were investigated.The present works forcuses on the development of W-Cu materials with special structure and high performance.In the second chapter of this dissertation,Cu-coated W powders(W-10Cu)were synthesized by electroless plating,W powders with average size of 0.8?m were used as the raw material.The as-prepared powders were pressed and sintered in H2 atmosphere to obtain sintered W-10 Cu samples.Phase constitution and morphology of the W-10 Cu composite powders were characterized.Density,microstructure and physical and mechanical properties of the sintered W-10 Cu samples were also investigated.The results show that the W-10 Cu composites powders have a core-shell structure with W particles coated by Cu.The powders exhibit good compactability and sinterability.The sintered W-Cu samples have homogeneous microstructure with W grain surrounded by Cu phase.The sintered W-Cu samples have a relative density above 97% after sintered at 1400°C.The electrical conductivity and thermal conductivity of the samples are 35%IACS and 192W/(m·K),respectively.And the bending strength and hardness reach 967 MPa and 377 HV,respectively.The thermal expansion coefficient is from 6.07 to 8.31×10-6K-1 in temperature range of 25-800°C.In the third chapter of this dissertation,copper-coated tungsten composite powders with different Cu contents were prepared by the electroless plating method.The W powders used for the electroless plating have different particle size distribution.Three-layered W-Cu(W-10Cu/W-20Cu/W-35 Cu,mass fraction)FGMs were fabricated by lamination pressing the W-Cu composite powders,followed by liquid phase sintering.Microstructure,interface structure and physical and mechanical properties of the graded materials were investigated.The experiment results show that relative density of the W-Cu FGM samples reaches 96.8% after sintered at 1350?C for 120 min.The W(Cu)elements have a graded distribution across the layers section,and the interfaces between layers have good conbination.The thermal conductivity of the W-Cu FGM samples reach 216W/((m·K),and the maximum bending strength and hardness is 1018 MPa and 359 HV,respectively.In the fourth chapter of this dissertation,Cu-coated W powders with different Cu contents and particle size were prepared by the electroless plating method.Functional graded W-Cu composite materials were obtained by lamination pressed the W-Cu powders,and subsequently microwave sintering at 1350?C for 40 min in a reducing atmosphere.The results show that relative density of the W-Cu FGM samples reaches 96.9%.Furthermore,the samples exhibit excellent physical and mechanical properties.The thermal conductivity of the samples reaches 210W/(m·K).The maximum bending strength and hardness reach 1004 MPa and 346 HV,respectively.