Nano-indentation study on the mechanical properties of TiC/Mo multilayers deposited by ion beam assisted deposition

Nanometer scale TiC/Mo multilayers with modulation wavelengths ranging from 2.5 nm to 13.7 nm have been prepared by ion beam assisted deposition (IBAD) system at approximately ambient temperature. The individual layer thickness was kept identical. The structures were analyzed by low angle X-ray diffraction, as well as plane-view transmission electron microscopy. The hardness and elastic modulus of these multilayers were thoroughly studied using a nano-indentation facility. It was found that the multilayer hardness was greater than the rule-of-mixture values. It also showed a dependence on the individual layer thickness arrangement. With the individual thickness property adjusted, the multilayer was even harder than its hard component (TiC). A maximum hardness of 21.40 GPa, approximately one time larger than that of the rule-of-mixture values, was found at λ=2.5 nm. A possible mechanism for hardening is discussed.