W-Cu Thermal, Electrical Conductivity Comparison of Different Process (1/2)

Except test of hardness, density and micro-structure, for tungsten copper composite materials, which is widely used in EDM electrode, high-voltage discharge tube and heat sink, test of thermal properties (includes thermal conductivity and the coefficient of thermal expansion) and electrical conductivity are also essential. There is the test result of thermal and electrical conductivity by three different kinds of process:

From the graph above, we can clearly see that among the three kinds of process, tungsten copper composite powder by PIM (Powder Injection Molding) has the highest thermal conductivity, reaches 217W/(m·k), compared with molding process and Cu infiltration. Combined with micro-structure of them, the researchers conclude some main reasons:

1. Although tungsten copper composite material has uniform distribution of W and Cu phase in the molding process, it still remains some porosity, which has a great impact on thermal conductivity of tungsten copper composite material;

2. Under the optimum Cu infiltration, there is no pore inside the sample, but Cu phase can not connect and form net structure. W and Cu phases distribute unevenly, in the process of heat conduction, part of thermal conductivity convey by W phase so that it is a critical factor of the lower thermal conductivity;

3. Relatively, injection molding process can effectively avoid the two defects, not only improve the density of tungsten copper products, but also W and Cu two-phase evenly distributed, thus it has a higher thermal conductivity.

Theoretically, thermal expansion of solid materials is due to the thermal vibrations of atoms as a center from its equilibrium position, which called crystal vibration non-harmonic effect. When the sintering temperature is increasing, atomic vibrations also stronger, the greater the energy of atomic vibrations, so that the microscopic atomic lattice parameters increase, the macro is manifested in the thermal expansion of solid materials. For single-phase material, the thermal expansion will increase as the temperature rises.

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