Strong orientation dependent hardness has been observed in both as-deposited and low-temperature annealed Ti/Ni multilayer thin films. The anisotropic hardness of as-deposited films is attributed to dominant deformation mechanism switch from dislocation pile-up against the interfaces to confined layer slip (CLS) within the layers as the loading direction changes from perpendicular to parallel to the interfaces. Additional strengthening of the multilayers is achieved after low-temperature annealing without noticeable microstructure modification due to temperature-induced grain boundary relaxation. This thermal strengthening is found to increase with decreasing layer thickness and increasing annealing temperature, and is more pronounced for loading directions parallel to the interfaces.

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