SI-traceability of XRD residual stress data by using Fe Kα radiation

XRD residual stress analyses by means of the conventional sin²ψ-method in accordance with standards EN 15305 or ASTM E2860 require well-aligned and calibrated X-ray diffractometers. The qualification of an X-ray diffractometer is performed by measurements of a stress-free powder sample and a certified ILQ reference sample from round robin experiments. In order to obtain reliable qualification results, the traceability of residual stress data to SI units is optimal, which can be achieved via Standard Reference Material 660c (LaB₆) from NIST. However, in many cases, such as the traditional residual stress analysis of ferritic steel samples using Cr Kα radiation, the peak positions and intensities of LaB₆ are unfavorable for SI-traceability measurements. The technical difficulties arising from this condition can be overcome by the application of Fe Kα radiation providing a diffraction peak of LaB₆ close to the ones of common materials. This work quantitatively investigates the usability of Fe Kα radiation for XRD residual stress analyses including SI-traceability of stress-free powder samples based on LaB₆. Moreover, its potential for multi-phase residual stress determination in duplex steels is demonstrated as a laboratory application example.