Hot-press Sintering, Structure Regulation And Properties Improvement Of Cu-W System Composites

Cu-W system composite has been applied in the field of electronic, electricalengineering, high temperature, navigation and aerospace because it combines theadvantages of Cu with good ductility, excellent thermal and electrical conductivityand W with high melting point, high strength and low coefficient of thermalexpansion. However, the properties, especially for thermal properties of Cu-Wcomposite cannot meet the demand of development of economy. Therefore, Cu-Wcomposite is prepared by improving processing, regulating the interface structureand adding the third phase to improve its properties.In order to get homogeneous Cu-W system composite, dense Cu was coated onthe surface of W powders forming Cu@W complex powders by electroless plating.The results showed that dense Cu@W complex powders could be attained when10mg/L two bipyridine was added as stabilizer, the reaction temperature was40°C andpH value was11.5.Cu@W complex powders were used as raw materials to fabricate20wt.%Cu-W composite by hot press sintering. The effects of coated Cu content for theCu@W complex powders on the microstructure and properties were discussed. Theexperimental results showed that the relative density of Cu-W composite reached upto99.3%at950°C-100MPa-2h, and W particles were distributed homogeneously inthe Cu-W composite forming Cu network structure. The densification mechanism ofCu-W composite in this chapter was mainly Cu-Cu sintering by using of Cu@Wcomplex powders reducing the W agglomeration and arch effect of W particles. Theproperties of Cu-W composite such as thermal, mechanical and electrical propertiesincreased with increasing Cu content coated on W powders. When20Cu@Wcomplex powders were used as raw materials, the comprehensive properties ofCu-W composite reached the best, which the maximum thermal conductivity was239W/(m K)，close to the theory value of20wt.%Cu–W composite; the coefficientof thermal expansion decreased to7.39×10-6/K, lower than reported value of8.7×10-6/K; the bending strength was976.7MPa, higher than reported value of670.4 MPa; vickers hardness was224.8HV, slightly lower than reported value of249.5HV;the electrical conductivity was50.6%IACS higher than reported value of24.7%IACS.Based on the second chapter, WC compounds were introduced into Cu-Wcomposite to modify the interfacial structure between Cu and W and to improve theproperties. So Cu-WC/W composite were fabricated using Cu@C/W complexpowders as raw materials which contained residual carbon. The results showed thatthe residual carbon increased from0.19wt.%to0.64wt.%when polyvinyl butyral(PVB) contents was from2.5wt.%to10wt.%at600°C. The WC compoundsaround W particles were synthesized in-situ in the densified Cu-WC/W compositeby hot press sintering. With WC compounds contents decreasing, the relative densityand properties of Cu-WC/W composite improved. When the content of WCcompounds was1.6wt.%, the comprehensive properties of Cu-WC/W compositereached the best. The thermal conductivity reached maximum value of287.5W/(m K), higer than the Cu-W composite value of239.0W/(m K) and reportedvalue of202.1W/(m K); coefficient of thermal expansion was4.39×10-6/K, lowerthan the Cu-W composite value of7.39×10-6/K and reported value of8.5×10-6/K;the bending strength was840.8MPa, lower than the Cu-W composite value of976.7MPa; vickers hardness was229.0HV, higher than Cu-W composite value of224.8HV; the electrical conductivity was47.7%IACS, slightly lower than Cu-Wcomposite value of50.6%IACS, but higher than the reported value of24.7%IACS.Based on the second chapter, carbon nanotube (MWCNT) was added intoCu-W composite to prepared MWCNT/Cu-W composite and the content MWCNTcontents and strengthening mechanism were studied. The experimental resultsshowed that MWCNT surface quality could be effectively modified by acid,sensitization and activation and multi-layer infiltration. Cu coated MWCNTcomplex powders (Cu@MWCNT) could be prepared by electroless plating in whichMWCNT was core. The Cu@MWCNT complex powders contained little Cu oxygenand impurity after reduction in the H2atomosphere. Densified MWCNT/Cu-Wcomposite could be prepared using Cu@W powders and Cu@MWCNT powders,and the MWCNT mainly existed in the Cu network structure improving thesinterability of Cu and MWCNT and avoiding the contact between MWCNT and W. The relative densities of MWCNT/Cu-W composite were all up to97%withMWCNT content increasing from0.1vol%to2.0vol%, and the thermal conductivityincreased from235.4W/(m K) to274.1W/(m K). When1.0vol%MWCNT wasadded, the comprehensive properties of MWCNT/Cu-W composite reached the best,which the thermal conductivity was274.1W/(m K), higher than239.0W/(m K) forthe Cu-W composite and the reported value of202.1W/(m K); coefficient of thermalexpansion decreased to5.23×10-6/K, lower than the Cu-W composite value of7.39×10-6/K and reported value of8.5×10-6/K; the bending strength was989.8MPa,higher than the Cu-W composite value of976.7MPa; vickers hardness was184.7HV,slightly lower than Cu-W composite value of224.8HV; electrical conductivity was52.5%IACS, close to Cu-W composite value of50.6%IACS. The improvementproperties of MWCNT/Cu-W composite could be abstribed to the addition ofMWCNT and the modified interface between Cu and MWCNT.