Grain-size-dependent thermal conductivity of nanocrystalline materials

In order to study the influence of grain size and lattice strain on the thermal conductivity of nanocrystalline (NC) materials, both experimental and theoretical studies were carried out on NC copper. The NC copper samples were prepared by hot isostatic pressing of nano-sized powder particles with mean grain size of 30 nm. The thermal behaviors of the samples were measured to be 175.63–233.37 W (m K)⁻¹ by using a laser method at 300 K, which is 45.6 and 60.6 % of the coarse-grained copper, respectively. The average grain size lies in the range of 56–187 nm, and the lattice strain is in the range of −0.21 to −0.45 % (in the direction of 111) and −0.09 to 0.92 % (in the direction of 200). In addition, a modified Kapitza resistance model was developed to study the thermal transport in NC copper. The theoretical calculations based on the presented theoretical model were in good agreement with our experimental results, and it demonstrated that the thermal conductivity of NC materials show obvious size effect. It is also evident that the decrease in the thermal conductivity of NC material can be mainly attributed to the nano-size effect rather than the lattice strain effect.