Mechanical properties of nanoscaled TiC/Fe multilayers deposited by ion beam sputtering technique

TiC/Fe nanoscaled multilayers with layer thickness of l_TiC = l_Fe = λ/2 (where λ is the modulation wavelength of the multilayers) ranging from 0.9 to 12.5 nm have been deposited on Si(111) wafers by ion beam sputtering techniques at nearly ambient temperature. Low-angle and high-angle X-ray diffraction (XRD) examinations were used to analyze the structural properties of the films. Mechanical properties of these multilayers were also thoroughly studied. The hardness and elastic modulus of these multilayers were determined using a Nanoindenter. The nanohardness showed a strong dependence on the modulation wavelength. It was found that the multilayer hardness was greater than the volume-weighted-mean of the component hardness. With the modulation wavelength adjusted, the multilayer was even harder than its hard component (TiC). A maximum hardness of 27.47 GPa, approximately one time larger than that of the rule-of-mixture values, was found at λ = 10.2 nm. A possible mechanism for hardening is discussed.