3D Mapping of Subsurface Cracks in Alumina Using FIB

Abstract

A new method has been developed to map cracks in 3D using focused ion beam (FIB) microscopy. Using the FIB, many parallel 2D slices are cut in the specimen. Imaging each 2D slice down several directions enables the 3D co-ordinates of features in the slice to be determined. Computer alignment and reconstruction of the 2D slices generates a 3D data set of the analysed zone. The 3D mapping method has been applied to the analysis of the cracks around an indentation site in a Al2O3-5vol.%SiC nanocomposite. This reveals the 3D location and morphology of radial and deep lateral cracks at the indent periphery, surface localised crack clusters, and a crack deficient zone close to the indent centre.

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

“…Figure 9 shows typical images of cracks observed underneath the residual indent impression for 100 and 200 g Vickers micro‐indentations. The main features of the 3D crack distribution uniquely determined from the multiple 2D FIB sections through the indents, consistent with previous studies (Cook & Pharr, 1990; Inkson et al , 2001b, 2006) were…”

“…This phenomenon was repeated for all indents sectioned sequentially in a single continuous direction from one side of the indent to the other. Such an asymmetrical crack distribution has been observed previously in 3D FIB analysis of similar Vickers indentations in polycrystalline alumina (Inkson et al , 2001b, 2006). Very recent work on indentation of thin coatings on steel does not show a marked asymmetry in the FIB‐sectioned thin‐film cracks generated by a spherical indenter (Xie et al , 2006; Ma et al , 2007).…”

“…Micro‐indentation of alumina generated a significant number of cracks that nucleate and propagate to relieve the high local stresses generated during the indentation process (see section ). 3D FIB tomography can be used to examine the 3D crack distribution in samples and is especially useful for the analysis of very localized damage such as from indents and scratches (Inkson et al , 2001b; Wu et al , 2003; Inkson et al , 2006; Xie et al , 2006; Ma et al , 2007). To study the effect of FIB milling on the observed residual indentation damage, including apparent crack distribution, Cr 3+ fluorescence scans were done before and after controlled FIB sectioning to evaluate stress changes.…”

“…A slice of material can also be removed for subsequent analysis in a transmission electron microscope (TEM) (Inkson et al , 2002; Cairney et al , 2004). 2D microstructural analysis can be extended to 3D by using 3D FIB tomography (Inkson et al , 2001a, 2001b; Steer et al , 2002; Wu et al , 2003). The 3D FIB tomography method involves milling serial cross sections through a surface by FIB, imaging each sequential 2D section (typically by secondary electrons (SE)), and then aligning the 2D images of the sectioned material to reconstruct the 3D microstructure using specialized software (ex.…”

“…Hockey, 1971; Page et al , 1992; Farber et al , 1993; Inkson, 2000). FIB has recently enabled the sectioning of alumina wear surfaces with a lateral accuracy of less than 50 nm, enabling both 2D site‐specific TEM sections to be extracted (Rubanov & Munroe, 2003) and 3D tomographic reconstruction of damage such as indentation and cracks in a volume of the order of 20 μm 3 to be carried out (Inkson et al , 2001b; Wu et al , 2003; Xie et al , 2006; Ma et al , 2007).…”