Abstract
The Cu/Invar bi-metal matrix composites have a great potential to be used as novel electronic packaging materials. In order to clarify effects of the Invar particle size on microstructures and properties of the composites, two Invar powders of average sizes of 26 μm and 105 μm were employed to fabricated the 50 wt% Cu/Invar composites, respectively, by spark plasma sintering (SPS) at 700–800 °C under vacuum condition with a heating rate of 100 °C/min, a pressure of 50 MPa and a holding time of 1 min. The results indicate that the Cu/ fine Invar (f-Invar) composites have finer Cu grain sizes in which the f-Invar particles are semi-continuously distributed. The composites have typical characteristics of low-angle Cu grain boundaries, high-density Σ3 growth twins and Cu/Invar coherent/semi-coherent interface. On the contrary, the coarse Invar (c-Invar) particles are discontinuously distributed in the Cu/c-Invar composites, resulting in the formation of coarser Cu grain sizes, high-angle Cu grain boundaries and non-coherent Cu/Invar interface. Moreover, compared with the f-Invar particles, the c-Invar ones can not only effectively decrease the Cu/Invar interfacial area, but also prohibit the Cu/Invar interface diffusion, therefore considerably improve thermal conductivity (TC) of the Cu/Invar composites at the cost of a little reduction of tensile strength (Rm). It is also clarified that properties of the Cu/Invar composites are sensitive to the sintering temperature. The 700 °C sintered 50 wt% Cu/c-Invar composite has the highest TC of 130.1 W/(m·K). It is very close to the theoretical value predicted by the Maxwell model and much superior to the TCs previously reported in the Cu/Invar composites of the similar Invar fraction.
NSTL
Elsevier