Thermal properties and thermal cycling stability of graphite/copper composite fabricated by microwave sintering

Abstract

Herein, graphite/copper (Gr/Cu) composites were fabricated by mechanical mixing and microwave sintering to investigate the effect of graphite volume fraction on the thermal conductivity (TC) and coefficient of thermal expansion (CTE) of the Gr/Cu composite. The TC and CTE of the composites were measured in the in-plane and through-plane directions. The obtained results revealed that the graphite volume fraction significantly affects the TC and CTE of Gr/Cu composites. A lower volume fraction led to higher thermal properties. The effect of thermal cycling on the thermal properties of metal matrix composites (MMCs) has remained largely unexplored. In this work, the effect of thermal cycling on the thermal properties of MMCs was investigated in a temperature range of −196°C/+200 °C. The thermal cycling resulted in a staged decrease of TC and a gradual increase in CTE. This could be mainly attributed to the CTE mismatch between the Cu matrix and the Gr phase. Observations by scanning electron microscopy (SEM) showed that thermal cycling created the micro-cracks and micro-voids in the composites, as well as the sliding and detachment of the Gr/Cu interface. The distribution of thermal stress and plastic strain during thermal cycling was simulated by the finite element method. The changes in TC and CTE are discussed regarding thermally induced stress.