Designing Novel Metallic Multilayer Nanocomposites Through Atomic Engineering of Interfaces – Influence of Heat of Mixing

Metallic multilayered nanocomposites have observed varying flow strength and indentation moduli values for the same type of interface. The enhanced mechanical properties from these nanocomposites have been attributed to their interfaces. The heat of mixing of the interface determines how much the two different layers have an affinity with each other and the resultant amount of shearing of the interface or transmission of dislocations through the interface. Nanoindentation of thin films on substrate technique is performed on five different metallic multilayer systems with a combination of FCC/FCC, BCC/BCC, and FCC/BCC interfaces to understand the effect of heat of mixing on its mechanical properties of hardness and indentation modulus of the films. In situ scanning probe microscopy (SPM) was done before and after each indentation. From the analysis, it is found that the heat of mixing has significant influence only in the hardness or flow strength values of the FCC/BCC multilayered nanocomposites due to dislocation plasticity mechanisms where the interface shear strength decreases with the change of heat of mixing from negative to positive values. The difference in the mechanical properties of FCC/FCC and BCC/BCC coherent multilayers are mainly due to either their lattice misfit or shear moduli differences, not the heat of mixing.