Evolution of residual stress and crack morphologies during 3D FIB tomographic analysis of alumina

Abstract

SummaryThree-dimensional focused ion beam (FIB) tomography is increasingly being used for 3D characterization of microstructures in the 50 nm-20 μm range. FIB tomography is a destructive, invasive process, and microstructural changes may potentially occur during the analysis process. Here residual stress and crack morphologies in single-crystal sapphire samples have been concurrently analyzed using Cr 3+ fluorescence spectroscopy and FIB tomography. Specifically, maps of surface residual stress have been obtained from optically polished single-crystal alumina [surface orientation (1ī 0 2)], from FIB milled surface trenches, from Vickers micro-indentation sites (loads 50 g-300 g), and from Vickers micro-indentation sites during FIB serial sectioning. The residual stress maps clearly show that FIB sputtering generates residual stress changes. For the case of the Vickers microindentations, FIB sputtering causes significant changes in residual stress during the FIB tomographic serial sectioning. 3D reconstruction of the crack distribution around microindentation sites shows that the cracks observed are influenced by the location of the FIB milled surface trenches due to localized stress changes.

3D analysis of crack morphologies in silicate glass using FIB tomography

“…3 and 4). This effect, also seen in FIB tomography of indents in alumina, 24 may arise (1) due to there being a size threshold for crack observation, possibly due to FIB sputtering of material into the finest cracks masking their presence, and/or (2) that the FIB sectioning procedure is resulting in some minor crack closure due to stress changes.…”

“…12,13,24 A significant feature of the 3D FIB tomographic analysis of the cracks in glass is that the density of circumferential cracks observed on the surface of the sample (by SEM, Fig. 2) is higher that the crack density observed beneath the indentation site (Figs.…”

“…12,24 In alumina it has been observed that the removal of the highly stressed central residual plastic damage zone of the indent during FIB tomography results in a reduction in both the residual stress and observed crack density in the remaining material. 24 For the silicate glass indents examined here, only a very small number of cracks to relieve stress were observed in the 2D FIB cross-sections through the Vickers indents compared to alumina samples indented with the same applied load. The residual stress existing in the indented glass was observed to drive time-dependant viscoelastic creep, discussed in the next section.…”

“…24 The change of stress is both a function of the geometry of the FIB-sputtered trenches cut into the material, and their location with respect to the preexisting microstructure and residual stress state of the sample, for example proximity to the central residual plastic damage zone of an indent. 12,24 In alumina it has been observed that the removal of the highly stressed central residual plastic damage zone of the indent during FIB tomography results in a reduction in both the residual stress and observed crack density in the remaining material. 24 For the silicate glass indents examined here, only a very small number of cracks to relieve stress were observed in the 2D FIB cross-sections through the Vickers indents compared to alumina samples indented with the same applied load.…”

Characterization of Fatigue Fracture in Ni-20 Pct Cr Alloys Using White Light Interference Microscopy and Scanning Probe Microscopy

“…In addition, focused-ion beam [5][6][7] tomography techniques are also increasingly used to characterize fractured surfaces. However, fractography results obtained using these techniques are qualitative in nature.…”