Grain rotations in ultrafine-grained aluminum films studied using in situ TEM straining with automated crystal orientation mapping

Abstract

In situ TEM straining allows probing deformation mechanisms of ultrafine-grained and nanocrystalline metals. While obtaining statistically meaningful information about microstructural changes using conventional bright-field/dark-field imaging or diffraction is time consuming, automated crystal orientation mapping in TEM (ACOM-TEM) enables tracking orientation changes of hundreds of grains simultaneously. We use this technique to uncover extensive grain rotations during in situ tensile deformation of a freestanding, ultrafine-grained aluminum film (thickness 200 nm, mean grain size 180 nm). During loading, both the fraction of grains that undergo rotations and the magnitude of their rotations increase with strain. The rotations are partially or fully reversible in a significant fraction of grains during unloading, leading to notable inelastic strain recovery. More surprisingly, the direction of rotation remains unchanged for a small fraction of grains during unloading, despite a sharp reduction in the applied stress. The ACOM-TEM measurements also provide evidence of reversible and irreversible grain/twin boundary migrations in the film. These microstructural observations point to a highly inhomogeneous and constantly evolving stress distribution in the film during both loading and unloading.

The Evolution of Growth, Crystal Orientation, and Grain Boundaries Disorientation Distribution in Gold Thin Films

“…It is undoubtedly believed that grain rotation and boundary migration are the universal and ubiquitous grain kinetics phenomena occurring during different stages of a film formation: growth, annealing, and cooling. Based on the available literature on grain rotation, it can be inferred that the grain rotation: viscous sliding or an independent rigid body rotation alone caused by annealing treatment in this study, is not enough to cause this drastic change in orientation, but this is enough and responsible to change grain and boundary orientation towards energetically favored condition, creating an optimum environment for grain boundary migration. Grain boundary motion between two differently orientated grains depends directly on the boundary surface energy causing the growth of the grain with low energy surface at the expense of high energy surface, resulting in the increase of <111> orientation and the grain size .…”

“…There are several works on the evolution of the microstructural characteristics of thin films under applied mechanical and thermal loads, which depend upon the recrystallization and grain kinetics processes . Grain boundary motion and grain rotation are described as the grain kinetics processes upon applied stresses in several literatures . In addition, twin mediated grain growth has also been observed when the films were subjected to a high mechanical stress .…”

“…This relative new technique utilizes electron diffraction patterns acquired from each section of the sample defined by the step size (spatial resolution up to 1 nm) to obtain crystallographic and structural information of grains and grain boundaries . Different films of metals and semiconductors have been analyzed by PED to study structural changes occurred during annealing and deformation processes, and the relative crystallographic orientation during a film formation …”

Grain Rotation in Plastic Deformation

“…Another TEM-based orientation mapping method, namely automated crystal orientation mapping, was proposed by R.A. Schwarzer in 1998 [44]. This method was developed to extend crystallographic orientation mapping to specimens that cannot be measured using EBSD-SEM techniques [44][45][46][47]. Particularly, it is very effective for severely deformed metals.…”

Oxidative decomposition products of synthetic NaFePO4 marićite: nano-textural and electrochemical characterization

“…An intensity of minimum 42 has been chosen in order to eliminate the points that presented a low reliability. This method of investigation has been already used for the study of different materials as thin films (Izadi et al, 2017;Wang et al, 2012), alloys (Rauch et al, 2012) and batteries (Norby et al, 2016). A region of interest of 1.2 μm 2 was chosen for the scanning area with a step size of 5 nm.…”