Main advantage using area detectors is that larger amount of data points can be used for analysis that result in a satisfactory measurement with short data collection time. Better insight of the sample material properties can also be seen when a 2D section of the diffracted Debye-Scherrer cone is analyzed instead of a 1D slice.
Xstress DR45 X-ray diffractometer takes advantage of this new technology.
X-ray diffraction detector comparison
In Figure 1 the physical dimensions of the two X-ray diffraction detector types are shown. In Table 1 the main characteristics of the X-ray diffraction detectors are tabulated.
| Feature | 1D detector | 2D detector |
|---|---|---|
| Number of pixels | 1 x 512 | 256 x 256 |
| Pixel size | 50 µm x 2500 µm | 55 µm x 55 µm |
| Active area | 64 mm2 | 196 mm2 |
| γ angle at 156° | 7.6° | up to 42.7° |
| X-ray detection efficiency | < 5% | > 90% |
In Figure 2 the gathered data from one exposure for both types of X-ray diffraction detectors is shown. After the data has been collected by the 2D detector, it is then integrated in the γ range into one dimensional “traditional” diffraction peak by integrating along the diffraction ring. This is shown in Figure 3.
Because of the additional dimension a new parameter, γ, is defined to represent the azimuthal angle on the diffraction cone. This angle is depicted in Figure 4.
Advantages that new X-ray diffraction detector technology brings to residual stress measurement
New detector technology enables residual stress measurement for materials with difficult properties. If crystal structure is not randomly oriented i.e., sample is textured, the 2D detectors’ increased γ range enables data collection even without mechanical oscillations.
Measurements with higher energy X-rays like Cu Kα radiation can be made in reasonable measurement times, due to higher X-ray detection efficiency.
The increased measurement speed thanks to 2D data integration and high X-ray detection efficiency makes small spot size measurements feasible in a short amount of time with minimal X-ray power.
Capability: residual stress measurement in highly textured materials
Highly textured materials are tricky to measure with a conventional diffractometer with 1D detectors. The diffracted Debye-Scherrer cone is not continuous, which makes the measurement routine more complex. Typically, different level of mechanical oscillations in both tilting and rotation are used. Figure 5 shows how the mechanical oscillations alter the detector data with 2D detectors.
Figure 6 shows that with 2D detectors the γ range can be used to collect data from a very textured material even without mechanical oscillations.
More versatility: Residual stress measurements without the need to change the X-ray tube
Kβ is a secondary wavelength generated by the X-ray tube that is about 15% the intensity of Kα. Due to its low relative intensity it is normally ignored or filtered out but with the improved sensitivity of the 2D detectors the Kβ can be used to make useful and relatively quick measurements. Traditionally an X-ray tube swap would be required (from Cr Kα to Mn Kα) to reliably measure Ferritic/Martensitic and Austenitic steels, but with the 2D detectors the Cr Kβ can be utilized possibly reducing the need for the additional X-ray tube.
Efficiency: Residual stress measurement on materials like titanium can be made in seconds
Titanium is light weight material with high strength, and it is a widely used material in aerospace industry. In aerospace industry material and manufacturing quality plays a huge role in safety. Residual stress measurement on titanium parts with Cu radiation has been challenging due to poor detector efficiency at higher energies.
With Xstress DR45 and new detector technology residual stresses can be measured in seconds. For example, with 2 mm collimator and 9 tilts over the tilting range of -45° to 45° measurement can be made in 69 seconds compared to several hours of measurement time with traditional detectors.
Summary
New Xstress DR45 diffractometer system with 2D area detectors excels when:
- process requires short measurement cycle time
- sample material is not optimal for X-ray diffraction
- measuring with small spot sizes (<1 mm collimators)