Ultra-strong and ductile amorphous-crystalline Ti-Zr-Hf-Nb-Ta/Co-Ni-V nanolaminate thin films

Films with a combination of high strength, large ductility, and high thermodynamic stability are always pursued for industrial applications. Here, we prepared the amorphous-crystalline Ti-Zr-Hf-Nb-Ta/Co-Ni-V nanolaminate with hardness and yield strength of 7.4 GPa and 3.8 GPa, and large deformability of similar to 70%. The ductility is attributed to two aspects. One is the Ti-Zr-Hf-Nb-Ta/Co-Ni-V layer interfaces acted as barriers to obstruct the propagation of nanocracks at the heavily deformed stage. Another is that amorphous layers acted as dislocation sinks promoting the dislocations to get annihilated when undergoing plastic flow, maintaining the plastic deformability of the crystalline layers. After annealing at 873 K for 1 h, the Co-Ni-V layer changes to a V-rich amorphous layer with minor nanocrystals, while the Ti-Zr-Hf-Nb-Ta layer transforms to a Ni-rich amorphous layer, due to the diffusion of Co and Ni. This chemical partitioning and consequent amorphization lead to the enhanced hardness and yield strength of 9.4 GPa and 4.5 GPa, but low ductility. In addition, the microstructure and mechanical properties of the nanolaminate can be further optimized by adjusting substrate temperature, layer thickness, and annealing process. The findings provide a new avenue for improving the mechanical properties of nanolaminates in a controllable manner.