Epitaxial growth and mechanical properties of (001) ZrN/W nanolaminates

Epitaxial growth of ZrN/W multilayers with bilayer periods Λ ranging from 2.5 to 50 nm has been achieved at 300 °C on MgO (001) substrates by means of dual ion beam sputtering, which is a novelty compared to polycrystalline growth reported so far in this system. X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) experiments reveal the following epitaxial relationship [110] (001) W // [100] (001) ZrN // [100] (001) MgO. Nanoindentation tests indicate a hardness increase proportional to Λ− 0.54, with maximum of 25.8 GPa at Λ = 2.5 nm. However, there is no hardness enhancement relative to rule-of-mixtures value, which could be ascribed to delamination at the W on ZrN interfaces, as observed by TEM and related to large compressive stress, as determined by XRD. Another explanation could be related to the small difference in shear modulus between the two materials.