The use of high-energy synchrotron diffraction for residual stress analyses

Residual stresses are formed due to inhomogeneous deformation gradients or temperature ®elds during the manufacturing and processing of components. In superposition with load stresses, they severely in ̄uence the strength and failure of components. For the non-destructive evaluation of the residual stresses in crystalline materials, well-developed angle dispersive methods for X-ray residual stress analysis exist at the surface and neutron residual stress analysis in the bulk of components [1±3]. Energy dispersive methods are employed in the case of neutron residual stress analysis at pulsed reactors and spallation sources using a time-of̄ight approach. First attempts at using energy dispersive methods in synchrotron diffraction (E , 50 keV) for residual stress analysis have been relinquished due to the poor resolution of Ge-detectors at that time [4, 5]. Today, improvements in the detectors and in the evaluation methods for the determination of the line position enable energy dispersive X-ray diffraction, which reaches penetration depths up to several mm but requires gauge volumes of the order of several mm [6]. Encouraged by this, recent experiments at the high-energy beam line ID15A in Grenoble, France, were performed, which revealed that residual stress analysis with a gauge volume more than one dimension smaller can be performed using high-energy synchrotron diffraction (HESD). The high-energy diffraction beam line ID15A of the European Synchrotron Radiation Facility in Grenoble, France, has an energy range up to E ˆ 1000 keV. The measurements were performed using an 80 ìm slit in the incoming beam and two 100 ìm slits in the re ̄ected beam. The diffraction angle was kept constant at 2è ˆ 108. Thus, the gauge volume is a parallelpiped with a length of 1650 ìm and a width of 145 ìm (Fig. 1). After identifying the re ̄ection, the lattice spacing d can be calculated according to Bragg's law, which can be written as a function of the energy E: d ˆ hc 2 sin è . 1 E hkl ˆ const: . 1 Ehkl (1)