Residual stress measurement on a magnesium sample

The problem

Conventional X-ray diffraction (XRD) residual stress measurements are pushed to the limit when the material has a large grain size or lots of texture. Results can be improved by using time consuming tilt and rotation oscillations to get a more averaged set of peak data for a given tilt angle. A customer needed a more efficient solution for measuring residual stress on a magnesium sample with challenging diffraction peak results.

The testing method

Measurements were done using Xstress G3 diffractometer with two types of detectors (Hamamatsu and MYTHEN2). Measurements were also carried out with Xstress DR45 that has 2D area detectors. A 3 mm collimator was used throughout the measurements. In the 1D detector measurements both tilt and rotation oscillations were used. Without them no diffraction data could be measured. With the 2D measurements only tilt oscillations were needed.

Figure 1. Peak data from 1D detectors without oscillations.

Figure 2. Magnesium sample measured with Xstress DR45.

The results

2D detector raw data shows notable discontinuity in the Debye-Scherrer diffraction ring (Figure 3) explaining the need for rotation and tilt oscillations in 1D detector measurements. 2D detector data is calculated by integrating the intensity along the diffraction ring and only tilt oscillation was needed to gather sufficient data.

Figure 3. Detector data from 2D detectors in Xstress DR45.

Total measurement time with 1D detectors was 1 hour 49 minutes. With MYTHEN2 detectors the exposure time could be reduced from 150 seconds to 30 seconds, but the total measurement time was reduced only by 35% because of all the necessary oscillation movements. Xstress DR45 with 2D detectors did the measurement in 3 minutes (Table 1).