Ultra-strength of Ti films via (002) texture optimization and nanocolumnar strengthening

This paper focused on the correlation between the (002) texture, columnar grain size and mechanical properties of Ti films prepared by magnetron sputtering. The (002) texture and columnar grain evolution were controlled under a combination of substrate bias voltage and argon flow rate. It was found that the substrate bias voltage was the key factor to dominate the (002) texture and columnar grain size. At constant substrate bias voltage of −100 V, all of Ti films showed a strong (002) texture. The micropillar compression test indicated that the Ti film with a strong (002) texture and nanocolumnar grain obtained an ultra-strength of 3838.2 MPa and an ultra-high work hardening exponent of 0.64 at substrate bias voltage of −100 V and argon flow rate of 20 sccm. The ultra-strength of Ti film stemmed from the fact that the nano-sized grain inhibited the generation of deformation twin and the (002) texture inhibited the activation of slips, and finally the slips with high Peierls-Nabarro stress were forced to be activated. Moreover, based on the TEM observation, the source of the ultra-strength of Ti film was explained by the proposed strength formula. Texture optimization and nanocolumnar strengthening are effective methods to improving the strength of pure Ti films. These results provided a new perspective of designing ultra-strength of Ti film materials.