Preparation And Properties Of Diamond/Cu Composites Fabricated With Double-layer Coated Diamond Particles

Diamond/Cu composites with high thermal conductivities,low coefficient of thermal expansions and isotropic physical properties have attracted extensive attentions in the world-wide.Aimed at solving the problems of low interfacial bonding strength and heterogeneous distribution of diamond,we adopted double-layer coated diamond particles combing with cold pressing and vacuum sintering method to fabricate diamond/Cu composites.This paper lays emphasis on the research of the improving of microstructure,interfacial combination,thermal physical properties and mechanical properties by carbide and copper coating.With this method,the high volume fraction of diamond/Cu composites with excellent properties were fabricated.The main results are as follows:With molten salt method,Mo and W were coated on the diamond surface.With magnetron sputtering method,Zr was coated on the diamond surface.With these coating layers,the interfacial wettability between diamond and copper matrix can be effectively improved.MoO₃ reacted with diamond surface at 1000? for 20?60 min.MoO₃ was first reduced to MoO₂.With long reaction time,MoO₂ completely transformed into successive even Mo₂C layer.WO₃ reacted with diamond surface at 1050? for 10?30 min.WO₃ was first reduced to WO₂.Then WO₂ was completely reduced and transformed into W,W₂C and WC.W/W₂C/WC layer formed on the diamond surface.Zr was deposited onto diamond surface by magnetron sputtering method.The diamond surface was heat treated at 700? for 5?30min.Zr partially reacted with diamond surface and ZrC layer formed.The outer pure Zr layer remained.Then ZrC/Zr layer formed on the diamond surface.After the diamond surface was coated with carbide,copper was electroless deposited onto the carbide.The volume fraction of copper in the double layer coated diamond particles was 5?50 vol.%.The double-layer coated diamond particles were mixed with copper powders and compressed with cold pressing to fabricated preforms.Then the preforms were placed into graphite dies and sintered with liquid phase under 1100? for 60 min in vacuum.The research results showed that the composites fabricated directly with 50?70 vol.%Diamond-Cu particles obtained the highest relative densities which were above 99%.The thermal conductivities?TC?of the composites gradually increased with the diamond content increased.The highest thermal conductivity was obtained with 65 vol.%diamond/Cu composites.With the diamond content in the range of 50?70 vol.%,the thermal conductivities of the composites fabricated with Cu-Mo₂C-Diamond,Cu-W/W₂C/WC-Diamond and Cu-Zr/ZrC-Diamond particles were 565?622 W·m^-1·K^-1,588?672 W·m^-1·K^-1 and 615?720 W·m^-1·K^-1 respectively.According to the AMM model and H-J model,the effect of thickness of coating layer is more important than the type of coating element on the interfacial thermal resistance.Comparing with molybdenum and tungsten layers,the ZrC/Zr layer is more effective.The outer zirconium layer diffused into copper matrix and thin zirconium carbide layer remained at the interface during sintering process.The thickness of zirconium carbide was only 300nm,which effectively reduced the interface thermal resistance.The coefficient of thermal expansion?CTE?decreased with the content increasing of diamond particles in the composites.The coefficient of thermal expansion of diamond/Cu composites increased with the increasing of temperature.With the diamond content in the range of 50?70 vol.%,the CTEs of composites fabricated with Cu-Mo₂C-Diamond,Cu-W/W₂C/WC-Diamond and Cu-Zr/ZrC-Diamond particles reached 5.40?7.63×10^-6K^-1,4.71?6.98×10^-6K^-1 and 4.33-6.62×10^-6K^-1 respectively.Kerner and Turner model were compared with the experimental values.The CTEs of 50?70 vol.%diamond/Cu composites matched well with the Kerner model curve,which indicated both shear stress and normal stress existed in the composites.The bending strength of 50 vol.%diamond/Cu composites fabricated with Cu-Mo₂C-Diamond,Cu-W/W₂C/WC-Diamond and Cu-Zr/ZrC-Diamond particles reached 178 MPa,213 MPa and 365 MPa respectively.The carbide layer improved the interfacial wettability and the copper coating layer improved the uniformity of diamond distribution,which effectively improved the mechanical properties.As for ZrC/Zr coated diamond/Cu composites,the outer zirconium layer diffused into copper matrix and the interface bonded by forming a solid solution.The inner zirconium carbide layer formed a stable chemical bonding.The designed coating layer increased the deformation resistance at the interface.So the highest bending strength was obtained.