Necking of invar layer in copper-invar laminates during roll-bonding

Abstract. Sheets of Fe-36%Ni (Invar) and copper alloys are bonded by roll-bonding process to produce metallic composites with a low thermal expansion coefficient and large conductivity. To boost the thermal conductivity of the composite, the Invar layers must be fragmented. For a given volume fraction of Invar, the necking/fragmentation depends on the spatial distribution of the Invar layers, meaning their number and thickness. Hence, different configurations of copper/Invar composites are processed to determine the effect of each parameter on the necking/fragmentation. The materials are then mechanically characterised to use the results as input data to the simulation of the process. Finally, to obtain a realistic simulation, a multi-step roll-bonding simulation using a remeshing solution is carried out for each cycle. The occurrence of necking during the cold-roll bonding of copper and Invar layers is both numerically and experimentally studied. In all cases, the experimental and simulation results are in good agreement. Invar layer thickness is of major importance to facilitate the fragmentation.