Size effect of the heat transfer in palladium-based metallic glass nanofilms

Abstract

Metallic glasses have special mechanical and electromagnetic properties because of their disordered atomic arrangements and are widely used in various fields including soft magnetic materials and micromachining. Metallic glass nanofilms are used as wear- and corrosion-resistant coatings, smart skins and thermoelectric materials. Research on the heat transfer in metallic glass nanofilms is crucial because local overheating during processing or in applications can lead to structural failures. There have been few reports on the heat transfer characteristics of metallic glass nanofilms. The present study measured the thermal conductivities of Pd80Si20 metallic glass nanofilms with thicknesses of 4.0–194.1 nm at room temperature using time-domain thermoreflectance. The thermal conductivity increases linearly with thickness in sufficiently thin nanofilms and the increment gradually decreases in thicker nanofilms. A model was proposed to predict the thermal conductivity of the Pd-based metallic glass nanofilms based on non-equilibrium molecular dynamics, surface scattering and ballistic transport theories. The predictions showed that electrons rather than phonons primarily dominate the heat transfer, while the size effect primarily depends on ballistic transport in nanofilms thinner than the electron mean free path, and on surface scattering in thicker nanofilms. The comparison with literature shows that when thicker than the electron mean free path, the metallic nanofilms have as good heat transfer performance as some bulk metallic glass.