Size effect on mechanical properties and deformation mechanisms of highly textured nanocrystalline Mo thin films

Abstract The size dependent hardness and strain-rate sensitivity of magnetron sputtered nanocrystalline Mo thin films with film thickness h ranging from 250 to 2000 nm were systematically investigated by using nanoindentation tests. Microstructure examinations manifested that all the as-deposited Mo thin films had a columnar-nanograined hierarchical structure with highly (110)-oriented growth texture, and the lateral columnar size went through a maximum of ∼60 nm at h = 1500 nm sample with h. Interestingly, both the hardness and strain-rate sensitivity exhibited a monotonic increment with reducing the columnar size. The underlying strengthening and deformation mechanisms could be interpreted in light of the confined slip of dislocations in the columnar grains, rather than the thermal activation of screw dislocations.