The relationships between the microstructure and the thermal conductivity of binderless WC have been quantified, considering crystal orientation, isotopic abundance, porosity, and grain size. A significantly higher conductivity is predicted in the out-of-plane (c-axis) direction vs. the in-plane (a-axis) direction, using first principles simulations. Isotopic enrichment of the tungsten sublattice is predicted to increase conductivity, e.g., by a factor of 4–5 in the absence of boundary scattering. The results suggest that for an isotopically pure single crystal a thermal conductivity exceeding 1000 W m−1 K−1 may be achievable normal to the basal plane. The conductivity of samples with various porosities could be well fit by a minimum surface area (exponential) model, with a porosity exponent of b = 4.4. Experiment and simulation show a strong grain size dependence to conductivity below 1 µm, with a saturation beyond ∼10 µm. The experimental plateau values for κ were ∼45 % lower than those of the simulations due to deviations from perfect stoichiometry. We also find a higher scattering coefficient in the experiments, likely due to effects of grain size distribution and elongation. Our study clarifies the physical origin of disagreeing literature reports as being predominantly due to grain boundary scattering and enables microstructural design for thermally demanding environments.

中文翻译：

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WC 的热导率：由第一性原理仿真驱动的微观结构设计


考虑到晶体取向、同位素丰度、孔隙率和晶粒尺寸，已经量化了无粘结剂 WC 的微观结构和热导率之间的关系。使用第一性原理模拟，预测面外 （c 轴） 方向的电导率明显高于面内 （a 轴） 方向。预计钨亚晶格的同位素富集会增加电导率，例如，在没有边界散射的情况下，电导率提高了 4-5 倍。结果表明，对于同位素纯单晶，垂直于基平面可以实现超过 1000 W m-1 K-1 的热导率。具有各种孔隙率的样品的电导率可以通过最小表面积（指数）模型很好地拟合，孔隙率指数为 b = 4.4。实验和模拟表明，晶粒尺寸对低于 1 μm 的电导率有很强的依赖性，饱和度超过 ∼10 μm。由于偏离了完美的化学计量，κ 的实验平台值比模拟值低 ∼45%。我们还在实验中发现更高的散射系数，这可能是由于晶粒尺寸分布和伸长率的影响。我们的研究澄清了不同文献报道的物理起源，主要是由于晶界散射，并使热要求苛刻的环境能够进行微观结构设计。