Strain rate-dependent hardness and deformation behavior in the nanocrystalline/amorphous Ti2AlNb film

Abstract

Abstract Building nanocrystalline/amorphous biphase nanostructure has recently emerged as a new strengthening-toughening route that can combine the strengthening benefits of nanocrystallinity and amorphization. Therefore, it is required exploring on the strain rate-dependent deformation behavior with above different nanostructure in certain system. Herein, three typical nanostructures: polycrystalline, uniform nanocrystalline/amorphous core-shell nanostructure and amorphous matrix with nanoclusters, have been achieved in the sputtered Ti2AlNb films by individually regulating the sputtering bias voltage (Ubias). Note that a high Ubias can promote formation of Nb–rich amorphous tissues via Al preferential resputtering and Nb segregation. Moreover, microstructural evolution and strain rate-dependent hardness and deformation behavior were further explored. Firstly, at a low Ubias (−40 V), Ti2AlNb film exhibited polycrystalline character; it yielded a relatively low hardness (~10.0 GPa) but a high strain sensitivity coefficient of 0.1505. Subsequently, the novel nanocrystalline/amorphous core-shell nanostructure consisting of Ti2AlNb nanocrystalline cores uniformly encapsulated by thin amorphous shells was achieved at a higher Ubias (−120 V); this nanostructure provided a remarkable hardness enhancement (~15.2 GPa) without sacrificing its ductility and intermediate strain sensitivity coefficient of 0.1382. Finally, a transition to amorphous matrix with nanoclusters occurred with further increasing Ubias to −200 V, thus yielding slight decrease in hardness (~12.5 GPa) and a minimum strain sensitivity coefficient of 0.0915 when shear-band deformation was activated.