Effect of porosity on the thermal conductivity of copper processed by powder metallurgy

Powder metallurgy is a preferred method of processing coppercarbon composites due to the non-wetting nature of these materials. Porosities are inherently introduced in these material systems, and adversely affect the thermal conductivity of the composite material, among other factors including interfaces and reinforcement distribution. In this work, we focus on the matrix material of pure copper and systematically analyzed the effect of volume fraction of porosities on the thermal conductivity. Spherical and dendritic copper powder materials were processed and it was found that the surface chemistry and morphology of particles affected the thermal conductivity apart from the porosity values. In order to study the effect of porosities alone, dentritic powder was used in the study. The thermal conductivity vs. porosity behavior showed three distinct domains. In all the domains the thermal conductivity decreases as volume fraction of porosities increases; however, in domain II, the decrease was much steeper than the other two. We are able to explain the variation based on the presence of interconnected and open pores in domain III to closed pores in domain I, and the transition occurring in domain II. None of the existing models capture the overall behavior. However, if we specifically account for the variation of number of grain boundaries with sintering, then the modified EMT model can match the experimental data.