THERMAL-CONDUCTIVITY AND ELECTRICAL-RESISTIVITY OF CEMENTED TRANSITION-METAL CARBIDES AT LOW-TEMPERATURES

The thermal conductivity, K, and electrical resistivity, rho, of cemented transition-metal carbides-a class of composites of high toughness-were measured for the first time at cryogenic temperatures. The dependence of these quantities on composition, grain size, and binder content was explored. The major qualitative findings are the following: (1) K for WC/Co grades has a gentle maximum ranging from 80 to 160 W/(m.K) around 150 K; (2) WC/Co has higher values of K and lower values of rho than TiC(x)/NiMo, because of vacancy scattering of electrons and phonons in the latter; (3) grades with larger grains have higher values of K; (4) grades with higher percentages of binder phase have lower values of K; (5) the lattice and electronic components of K are comparable for TiC(x)/NiMo; (6) multicarbide grades have lower values of K than WC/Co; (7) a Callaway analysis of the lattice component of K identifies scattering of phonons by grain boundaries, point defects, electrons, and other phonons as significant for these materials, with defect scattering dominating in the liquid-nitrogen range.