No abstract

For the first time metal matrix composites have been investigated by 3D computed tomography combined with enhanced interface contrast due to X-ray refraction. The related techniques of refraction topography and refraction computed tomography have been developed and applied during the last decade to meet the actual demand for improved non-destructive characterization of high performance composites, ceramics and other low-density materials and components. X-ray refraction is an optical effect that can be observed at small scattering angles of a few minutes of arc as the refractive index n of X-rays is nearly unity (n = 1 − 10−6). Due to the short X-ray wavelength, the technique determines the amount of inner surfaces and interfaces of nanometer dimensions. The technique can solve many problems in understanding micro and sub microstructures in materials science. Applying 3D refraction computed tomography, some questions could be clarified for a better understanding of fatigue failure mechanisms under cyclic loading conditions.

Modern materials research in the field of aeronautics seeks new methods to improve the performance of combustion engines and turbines by reducing weight using materials with high specific strength and stiffness. [1] Since the growth of international air traffic is about 5 % per year and the market demands economical turbines the need of lightweight materials becomes clear. [2] One way to achieve this objective is to use metal matrix composites (MMC). Most promising is the combination of SiC fibers together with TiAl6V4 (Ti-MMC). As Titanium 6±4 can be easily diffusion bonded, one fabrication route is the hot isostatic pressing (HIP) of Ti-coated SiC fibers.A feasibility study has been carried out by MTU Aero Engines, which proofed a possible weight reduction by 25 % using Ti-MMC.Most recently the successful application of this composite material as a landing gear component has been reported in literature. [3] The aim of this combination is to take advantage of the high Young's modulus of the SiC fibers and the low weight of Titanium (high specific stiffness). The SiC fibers, which are

No abstract

X-Ray Refraction Topography techniques are based on Ultra Small Angle Scattering by micro structural elements causing phase related effects like refraction and total reflection at a few minutes of arc as the refractive index of X-rays is nearly unity (1⋅10 -5 ). The extraordinary contrast of inner surfaces is far beyond absorption effects. Scanning of specimens results in 2D-imaging of closed and open pore surfaces and crack surface density of ceramics and foams. Crack orientation and fiber/matrix debonding in plastics, polymers and ceramic composites after cyclic loading and hydro thermal aging can be visualized. In most cases the investigated inner surface and interface structures correlate to mechanical properties. For the exploration of Metal Matrix Composites (MMC) and other micro structured materials the refraction technique has been improved to a 3D Synchrotron Refraction Computed Tomography (SR-CT) test station. The specimen is situated in an X-ray beam between two single crystals. Therefore all sample scattering is strongly suppressed and interpreted as additional attenuation. Asymmetric cut second crystals magnify the image up to 50 times revealing nanometer resolution. The refraction contrast is several times higher than "true absorption" and results in images of cracks, pores and fiber debonding separations below the spatial resolution of the detector. The technique is an alternative to other attempts on raising the spatial resolution of CT machines. The given results yield a much better understanding of fatigue failure mechanisms under cyclic loading conditions.