The Effects of Composition and Microstructure on the Thermal Conductivity of Liquid-Phase-Sintered W-Cu

Liquid-phase sintering of high-purity, submicron, co-reduced W-15Cu powders at temperatures of 1463 to 1623 K (1190 to 1350 A degrees C) produces W grain sizes ranging from 0.6 to 1.2 mu m while maintaining less than 2 pct porosity. Measured thermal conductivities of 185 to 221 W/(m center dot K) are related to the grain size and contiguity, which ranged from 0.51 to 0.62. The effects of composition and microstructure on thermal conductivity are further investigated with a model based on a computational cell that allows adjustment of the grain shape to produce selected matrix volume fractions and contiguities. The model considers porosity, the effects of transition metal impurities on the thermal conductivities of the W and Cu phases, and the role of an interfacial resistance between W grains. The effects of grain size and contiguity on thermal conductivity are shown for thermal boundary conductances ranging from 0 to 1.7 x 10(10) W/(m(2)center dot K). Comparison of the model predictions with those of prior models, the experimental results, and previously reported thermal conductivities shows that impurities are highly detrimental to the thermal conductivity, but the thermal boundary conductance is a significant factor for high-purity W-Cu.