High energy X-ray refraction system to characterize inner surfaces or interfaces in materials

摘要

X-ray refraction is a relatively new technology for the characterization of inner surfaces or interfaces in structures. When an X-ray crosses an interface in an object, X-ray refraction occurs. The index of refraction, n=1-δ, where δ～1x10~(-6) for typical X-ray energies, leads to refraction angles of several arc seconds. As the X-ray energy increases, the refraction angle decreases, making it more difficult to separate the refraction beam from the main X-ray beam. Most X-ray refraction work has used low energies, typically under 35 keV. The penetration of X-ray beams with energies below 35 keV is poor, limiting the method to low density objects or very small samples. It is desired to apply this method to larger samples of aerospace materials such as aluminum and titanium alloys and composite structures. The ability to nondestructively detect micro-porosity and crack initiation at length scales of 0.1 to 100 microns would greatly advance the understanding of the properties of these materials. In particular, this will enable the detection of very small cracks generated in the early stages of fatigue during a specimen life cycle. In our current work, we are evaluating the use of high energy polychromatic X-ray beams to generate refraction signals from material discontinuities. This paper includes the design and preliminary results for our high energy refraction system. We have demonstrated a refraction signal at boundaries using a filtered 120 kVp beam. We also discuss the limits to refraction analysis, and describe our plans for further development of our X-ray refraction system.