SS OCCurs due
5 nig arrangement of the pores and the walls. A 3D rendering of an aluminum foam is presented in figure
ue. This magi 3. The deformation modes of this foam can be studied by compressing a sample and imaging by
150000 3 ye 0 tomography the internal structure at different stages of deformation (5). Microtomography at
Bult devigogs medium resolution can also be performed on dense materials. We have for instance studied a
NONE 4 ge composite formed by an aluminum matrix containing ZrO,/SiO, spherical particles the size of
dl Contrast in which has been selected between 40 and 60 um. What we aim to image in that case is the
fluctuation of the density of the particles, to analyze the presence of clusters in the microstructure
cnc whe iy (see the 3D rendering in figure 4).
mers, but High resolution microtomography is a necessary tool when the details of the microstructure to
analyze is of the order of 1 um. This technique has now been employed at ESRF for three years. It
bY incesing fy can give pictures with a very high level of details. We have used it for microstructural studies of
alive way mail alloys. Figure 5 shows a granule of Al + 5% Cu binary alloy obtained by the impulsed atomisation
of imposing bt process (6). Primary (elongated) and secondary dendrites of aluminium can clearly be seen in gray
4 Widely opened) along with eutectic zones in lighter gray. But one can also see micro shrinkage pores in dark, which
He tanks to i were completely undetectable by standard metallography, because both of their small size and the
pr —— fact that they get plugged during the polishing process. Figure 6 shows a reconstructed image of a
send m specimen of aluminium cast alloy (AS7G03). The silicon eutectic particles which appear during the
sedan 2 solidification between the primary dendrites represent a very important microstructural feature of
comedy such alloys as their size, shape and spatial arrangement play a key role on the mechanical properties
Na in spite of their small size (around 2 um in the present case) and of their x-ray attenuation which is
Wil espe i very close to this of the matrix, These particles could be clearly imaged by edge diffraction.
secon of mag Figure 7 shows an example of the holotomographic approach applied to a polystyrene foam. Phase
imaging allows to distinguish easily the polymer (dark in the reconstructed slice) from the void in
this sample that is basically non-absorbing. The mass density is quantitatively mapped in each point
of the sample. The images show a single foam cell enclosed by a very thin (few micron) polymer
wall. The shape of the cell is irregular and distorted, probably due to a crushing process. In this
example four sample detector distances were used for retrieving the phase and 700 angular positions
for the tomography. Phase imaging, both in the edge detection and the holotomographic mode, is
also used to study the rheology of aluminium-silicon alloys in the semi-solid state. (RRR Salvo
tomobook and RRR Peter tomobook).
7 Quantitative results
Microstructure
3D images provide a new insight into the analysis of the microstructure of the materials. The
commonly admitted hypothesis which where necessary to retrieve the desired 3D parameters from
the information available in 2D can now be checked and comforted or rejected. Real 3D parameters
like the percolation degree of a reinforcement in a matrix, which is of crucial importance for the
modeling of the mechanical properties of the materials can now be assessed. A lot of effort is being
currently devoted to the analysis of the images in 3D to measure quantitatively the morphological
parameters characterizing different microstructures. Examples of size or aspect ratio histograms for
ceramic particles in a metallic matrix in 3D can for instance be found in (4). In order to simplify the
interpretation, we produce simple model materials with spherical particles and heterogeneous
structures (see Fig. FFF).
‚he analysis of the
ver‘ ow densily
moles can be ve)
What is imaged 1
eo and the MEX
23
