Present and Future Use of High-Energy X-rays for Industrial Materials Research
Yan Gao
GE Global Research, Niskayuna, NY 12309
The past few years have witnessed drastic increases of fundamental and applied research activities based on high-energy X-rays, as the third-generation synchrotron sources world-wide, including APS, have entered their matured and user-friendly operational stage. Use of high-energy X-rays (~50-90 keV) has, in many areas, revolutionized the way of materials characterization in industrial research laboratories. In collaborating with researchers at APS and NSLS, we have carried out a number of high-energy X-ray experiments using various X-ray techniques, including diffraction, fluorescence, and absorption spectroscopy, and these projects have demonstrated the unparallel advantages of what high-energy X-rays can do for industrial users. While a third-generation source is always the first and best choice for high-energy X-ray work, reasonable flux can also be achieved at a second-generation source by using a sagittal focusing Laue monochromator[1].
Several past projects will be used as examples in this talk. One is on non-destructive residual stress measurement of shot-peened alloys. The conventional way to obtain a depth profile is through layer-removal, but that unfortunately destroys the sample for further testing and the results could be inaccurate. By using high-energy X-rays and a triangulation slit system, residual stress can be measured as a function of depth non-destructively[2]. Figure 1 is the setup for such a measurement at the APS XOR 1-ID-C beamline.
Figure 1. Non-destructive residual stress measurement at APS 1-ID-C beamline. A shot-peened cylindrical sample is mounted in a 4-circle diffractometer on a sample stage that rotates and moves longitudinally to increase the number of grains irradiated by X-rays. Triaxial strain tensor can be obtained from such measurements.
Combined with 2D detector and auto-sampler, high-energy X-rays are an ideal tool for high-throughput transmission powder diffraction. This is especially useful for highly absorbing materials (such as metal and ceramics) for which the sample as thick as a few mm can be measured. High quality data, in terms of signal to noise ratio and angular resolution, can be obtained in seconds to minutes for qualitative and quantitative phase analysis, and therefore tremendously boost the productivity when large number of samples are to be analyzed, not only from the speed of measurement but also due to simplified sample preparation. Examples along this line include XRD and SAXS on Oxide Dispersion Strengthened (ODS) alloys (Figure 2), and Rietveld analysis on thermal barrier coatings (TBC) materials.
Figure 2. Cast ingots of ODS alloys containing nanosized oxide particles. Characterization of their dispersion represents a typical industrial problem that requires high-throughput diffraction techniques such as XRD and SAXS[3].
While most XAFS work is carried out below 20 keV, some materials may require excitation of higher energy photons. Our most recent work at APS involved EXAFS at Pr K-edge (42 keV) for quantum-splitting phosphor materials LaPO4:Pr, for which Pr L-edge measurement is hampered by the presence of La. High-energy excitation is also advantageous for fluorescence measurement when deep buried heavy elements, such as Hg with K-edge at 83 keV, are to be detected.
The future of high-energy X-rays, as well as synchrotron facilities in general, may play an important role in shaping materials research for both academia and technology-driven companies like GE. Advanced materials research in many areas demands cutting-edge characterization tools using brighter and smaller X-ray probes for microdiffraction and microfluorescence measurements to obtain structural and compositional information with highest spatial resolution. In-situ time-resolved measurements that may hold the key to the mechanistic understanding of many chemical or physical processes, such as the catalytic mechanism of hydrogen storage materials, is another interesting area to further explore, and use of high-energy X-rays and a high-speed 2D detector[4] have made it more feasible than ever before. In addition to the need for innovative synchrotron technologies, the challenges that many industrial users face are their extremely diversified needs in various X-ray techniques, constraints in materials from their real-world problems, and accelerated research cycles driven by companies’ business strategies. While the synchrotron facilities correctly focus on the most advanced capabilities and research, today’s industrial users also need access to tools that will enable short-term characterization tasks to solve critical business problems, and such projects may require not only state-of-the-art instrumentation but also quick access, dedicated instrumentation for frequently used analyses, and turnkey facilities. In short, we hope the future synchrotron facilities will be more advanced in technology, easier to access, and friendlier for users.
Acknowledgement: Ulrich Lienert, Jon Almer, Dean Haeffner (APS); Zhong Zhong (NSLS); Qing Ma (APS DND-CAT); Bill Carter, Tom Angeliu, Jim Ruud (GE).
[1] Z. Zhong, C.C. Kao, D.P. Siddons and J.B. Hastings, J. Appl. Cryst. (2001), 34, 504-509.
[2] U. Lienert, J. Almer, D. Haeffner, Y. Gao and W. Carter, Synchrotron Radiation Instrumentation: Eighth International Conference, Edited by T. Warwick et al. (2004), 1074-1077.
[3] T. Angeliu, et al. “Microstructural Characterization of Commercial Oxide Dispersion Strengthened Materials, 2003GRC391, March 2004
[4] Such as amorphous silicon based GE Revolution detector that is 41x41 cm in size with readout time in milliseconds.
