Thermal Conductivity Behavior of Bimodal Nanocrystalline Cu-Ag Material

Bimodal nanocrystalline (nc) Cu-Ag composites and nc Cu were prepared by a high pressure sintering method in an argon atmosphere. The samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The thermal conductivity of the samples with an average grain size from 50 nm to 270 nm was measured at 200-400 K by a laser method. The results show that the thermal conductivity of nc Cu-Ag and nc Cu increases with the grain size or temperature increasing. At 300 K, the thermal conductivity of the bimodal nc Cu-Ag with an average grain size of 150 nm is 163.45 W/m.K, which is 40.7% and 38.1% of that of the coarse grain Cu and Ag, respectively. The thermal conductivity of the samples was also measured by the modified Kapitza thermal resistance model and the theoretical calculations are in good agreement with experimental results. The thermal conductivity of bimodal nc Cu-Ag is much lower than that of monocrystalline Cu/Ag bulks. It is concluded that the thermal conductivity of bimodal nc Cu-Ag is increased with the grain size increasing, which exhibits an obvious size effect in a certain grain size range. Key words: bimodal nanocrystalline Cu-Ag; thermal conductivity; grain size; Kapitza resistance