Micro-structure Control And Properties Of W-Cu System Composites

The tungsten-copper（W-Cu）system composites are widely used owing to combination of the high mechanical properties and good ablation resistance of tungsten as well as the high thermal and electrical properties of copper.The composites are often used as electrical packing material,heat sink or electrode of large scale integrated circuit,high power microwave device and LED lighting system in the fields of aeronautics,astronautics and military.However the W-Cu system composite is a kind of pseudo-alloy which composed of two immiscible metal phases.The difficulties between properties of two elements,especially melting point,thermal expansion coefficient and wetting ability,lead to a huge problem for preparing material with high relative density,proper micro-structure and perfect properties.Based on papers and previous experiments,our goal was to prepare the dense W-Cu system composites in low temperature with the help of minor activated sintering element added by electroless plating coating method.Then we added minor interfacial transition ceramic phase by using carburization process of organic additives and high temperature ceramization process and control the phases and structure to improve the interfacial thermal conductivity also the overall thermal property.Several highly pure coated powders with accurate layer content were prepared and characterized.Also the densification,structure and properties of sintered W-Cu system composites are investgated.Firstly,the low temperature desification,structure and properties of Ag-Cu/W system composites are studied.The Cu@W coated powders were obtained with high purity during the preparation process.Small amount of Cu₂O phase in Ag@Cu coated powders were removed using deoxygenation treatment method in controlled atmosphere furnace.Minor Ag-Cu solid solution formed from Ag sintering aid and Cu metal matrix during heat preservation.Capillary force pushed the liquid-phase alloy to fill the voids in Cu metal matrix,contributing to the low temperature densification of the sintered sample.In the meantime,high thermal conductivity was guaranteed for not having too much metal solid solution.Electrical conductivity was also improved for elemental Ag.The relative density of the Ag-Cu/W system composite with 2 wt.%Ag reached 98.47%(sintering temperature was 850 ^oC,density was 15.48 g?cm^-3,thermal conductivity was 227.4 W/（m·K）,electrical conductivity was 52.4%IACS).Secondly,the interfacial improvement,structure and properties of W_xC-W/Cu system composites are studied.The C content at the interface between W and Cu was much higher than that in two phases of the Cu@W_xC@W coated powders,indicating that obvious transition layer existed at the interface.W_xC@W coated powders were prepared using high temperature ceramization method（When treatment temperature was 1050 ^oC,the layer phase was a mixture of WC and W₂C.When treatment temperature was 1200 ^oC,the layer phase was mainly WC）.The W_xC-W/Cu system composites were obtained by using hot-press sintering（sintering temperature was 850,pressure was 100MPa,soaking time was 2h）.Interfacial transition phases existed at the interface between two phases,mainly surrounding the W particles in random positions.The thermal conductivity of the W_xC-W/Cu system composite was influenced by the treatment temperature of W_xC@W coated powders.When the layer phase was mainly WC,there was a clear improvement in the thermal conductivity for the modification of interfacial property.Also the modification for thermal conductivity was affected by the content of transition layer.When the addition of PVB content was 1.5 wt.%and treatment temperature was 1200 ^oC,the thermal conductivity and relative density of W_xC-W/Cu system composite were 96.1%and265.1 W/（m·K）,respectively.