TiN/NbN multilayers and TiN monolithic films have been grown by UHV reactive magnetron sputter deposition on MgO single crystals. The hardness has been measured by nanoindentation and the as-deposited and deformed structures studied in cross-section using transmission electron microscopy. It has been found that initially the multilayers grow epitaxially with the substrate. However, once the overall film thickness has reached ∼300 nm, epitaxial growth ceases. No increase in hardness with respect to monolithic films of the multilayer components is observed in these multilayers. Experiments on monolithic films of TiN show that the same loss of epitaxy occurs, leading to a reduction in the hardness of the films, and that this change in growth morphology is triggered by the internal stresses induced within the films during deposition.