High resolution x-ray tomography applied to the observation of the micro- 
structure of materials. 
Eric Maire”, Jean-Yves Buffi@re‘, Peter Cloetens*, Wolfgang Ludwig* and G Peix** 
" CNRS GEMPPM INSA de LYON, Villeurbanne (F) 
* ID19 beam line. Estf Grenoble (F) 
** CNDRI INSA de LYON, Villeurbanne (F) 
Introduction 
X-ray tomography is a non destructive technique which permits to obtain three-dimensional (3D) 
images of the interior of a material. It shows all the microstructural features (other phases, 
inclusions, cracks, pores, ...) inducing a modification of the attenuation or of the optical phase along 
the path of the beam. It has been used in medicine for about 30 years with a typical resolution of 
around 300 microns. Recently, third generation synchrotron radiation facilities became available. 
When working at the first of these new sources, the European Synchrotron Radiation Facility 
(ESRF) in Grenoble, it was possible to improve the resolution to the micron level. This allows the 
extension of this technique to the field of 3D "materiallography” i.e. the observation of the 
microstructure of materials in 3D. More precisely, when coupled with a tensile stage, the 
microtomographic equipment installed at beamline ID19 has permitted to obtain 3D images of the 
microstructure of the materials as well as their evolution under load. 
The aim of this paper is to show that x-ray microtomography is now a very powerful tool to 
investigate the microstructure and the deformation mechanisms of a wide range of materials, which 
range from foams and alloys to rocks or snow. The principle of the technique, both in its medium 
and high resolution forms, will be presented. The recent improvements will be emphasized. 
Qualitative and quantitative illustrations will be given in the field of materials science. 
Principle of the technique 
X-ray radiography 
The x-ray radiography technique is based on the simple Beer-Lambert law [1] which gives the ratio 
of Nj, the number of photons transmitted after a path of length x through the thickness of a sample 
exhibiting a coefficient of attenuation p, over No, the number of incident photons. If u varies along 
the path, the integral of u over x has to be used: 
Mi exp|- | ux y, 2)dx 
N, : 
path 
wu depends on the composition of the local element of matter situated in x,y,z according to a law of 
the type: 
Z* 
ux, y, z) = Kops 
By 
[2] 
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