Size dependent mechanical properties and deformation mechanisms in Ti and Zr films

The nanometallic Ti and Zr monolayer films with various thicknesses ranging from 600 to 2200 nm were prepared by using magnetron sputtering technique. The microstructure results demonstrated that Ti films transformed from hcp to fcc at t ≤ 600 nm, while Zr films were grown with hcp structure of nanocolumnar grain. Moreover, the grain orientation of hcp Ti films changed from (0002) preferred orientation at t = 1200 nm to random orientation at larger thickness. Subsequently, the hardness and strain rate sensitivity of films were explored by nanoindentation. The Hall-Petch relationship is obviously invalid to explain the film thickness dependent hardening behaviors in Ti and Zr films, and the influence of phase structure, orientation and residual stress on nanoindentation hardness was discussed. It seems that residual stress plays an important role in the determination of hardness in present Ti and Zr films. The negative strain rate sensitivity m appeared during the plastic deformation of fcc Ti films, which is caused by the phase transformation. The underlying deformation mechanism of hcp Ti and Zr films was also discussed.