Microstructure, grain boundary evolution and anisotropic Fe segregation in (0001) textured Ti thin films

TL;DR

This study presents a method to produce bicrystalline titanium thin films with well-defined grain boundary faceting and anisotropic iron segregation, revealing how boundary structure influences solute distribution.

Contribution

It introduces a deposition process to create pure tilt grain boundaries in Ti films and demonstrates the relationship between CSL density, faceting, and Fe segregation behavior.

Findings

Bicrystalline Ti films with $ ext{Σ}$13 CSL boundaries were achieved.

Grain boundary faceting into symmetric and asymmetric segments was observed.

Preferential Fe segregation occurs in specific boundary segments, influenced by CSL density.

Abstract

The structure and chemistry of grain boundaries (GBs) are crucial in determining polycrystalline materials' properties. Faceting and solute segregation to minimize the GB energy is a commonly observed phenomenon. In this paper, a deposition process to obtain pure tilt GBs in titanium (Ti) thin films is presented. By increasing the power density, a transition from polycrystalline film growth to a maze bicrystalline Ti film on SrTiO$_3$ (001) substrate is triggered. All the GBs in the bicrystalline thin film are characterized to be $\Sigma$13 [0001] coincident site lattice (CSL) boundaries. The GB planes are seen to distinctly facet into symmetric {$\bar{7}520$} and asymmetric {$10\bar{1}0$} // {$11\bar{2}0$} segments of 20-50~nm length. Additionally, EDS reveals preferential segregation of iron (Fe) in every alternate symmetric {$\bar{7}520$} segment. Both the faceting and the segregation are explained by a difference in the CSL density between the facet planes. Furthermore, in the GB plane containing Fe segregation, atom probe tomography is used to experimentally determine the GB excess solute to be 1.25~atoms/nm$^{2}$. In summary, the study reveals for the first time a methodology to obtain bicrystalline Ti thin films with strong faceting and anisotropy in iron (Fe) segregation behaviour within the same family of planes.