The properties of components and semi-finished products depend not only on geometrical dimensions but also strongly on the material properties such as the microstructure and the texture as well as on the residual stress state. The microstructure, the texture and the residual stress distribution are particularly inhomogeneous throughout the component in the case of local high thermal or mechanical loading such as in welding processes and in conversion processes. Thus, often very small gauge volumes are necessary in order to find local extrema e.g. of the texture and the residual stresses.

A non-destructive quantitative texture and residual stress analysis can be performed using diffraction methods. The easiest accessible radiation is conventional characteristic X-radiation (e.g. ECuK1 = 6.9 keV, ECrK1 = 5.4 keV), which has a penetration depth of some ten µm and therefore is only suitable for the determination of the residual stresses in near surface layers. Neutron diffraction can provide information at significantly higher depths of several 10 mm's in components, but for intensity reasons the local resolution of neutron residual stress analysis is in the order of a gauge volume size of approximately 1 mm3.

Using high energy synchrotron radiation (Energy range up to 300 keV), for instance in light-weight materials such as Al-alloys, penetration depths comparable to neutrons are achievable while significantly smaller gauge volumes ­ potentially as small as 60 µm x 60 µm x 0.6 mm ­ can be realised thanks to the high intensity and parallelism of the beam. Thus, white high energy synchrotron radiation at the ESRF was employed for strain and stress analyses on a variety of materials and problems [1].

The use of white high energy synchrotron radiation enables a simultaneous analysis of residual stresses, texture and phase composition with high local resolution in cold extruded steel rods (Figure 110) with a diameter as large as 15 mm. Figure 111 shows the spectra obtained during approximately 30 minutes each in the centre and near the surface of the cold extrudates. The spectra illustrate the decrease of strength of the <110> fibre texture towards the outer border of the extrudates [2]. The consequence of this texture inhomogeneity is an inhomogeneity of the mechanical properties present across the diameter of the sample. Subsequent residual stress analyses (Figure 112) revealed the residual stress state. The residual stress distribution and the quantitative values support the results of FEM calculations and enable an optimisation of the process parameters such as the extrusion ratio, die opening angle and the ejection method.

Further measurements performed on thermal barrier coatings, functionally graded Ni/ZrO2 materials and ceramic matrix composites revealed that, using high energy synchrotron radiation, residual stress analyses with a local resolution of a hundred micrometres are possible.

Principal Publications and Authors
[1] W. Reimers (a), A. Pyzalla (a), M. Broda (a), G. Brusch (a), D. Dantz (a), T. Schmackers (a), K.-D. Liss (b), T. Tschentscher (c), J. Mat. Sci. Lett., 18, 581-583 (1999).
[2] A. Pyzalla (a), W. Reimers (a), A. Royer (b), K.-D. Liss (b), Proc. 20th Risoe International Symposium on Materials Science: Deformation-Induced Micro-structures: Analysis and Relation to Properties, ed. J.B. Bilde-Soerensen et al., Risoe National Laboratory, Roskilde, Denmark, 453-458 (1999).

(a) Hahn-Meitner-Institut, Berlin (Germany)
(b) ESRF
(c) HASYLAB, Hamburg (Germany)