Nondestructive Testing of Single Crystal Alloy by X-ray Diffraction

In the aerospace industry, quality control of mono-crystalline metallic alloys, such as those found in turbine blades, is mandatory. Control can be performed with a variety of X-ray methods known as Laue diffraction techniques. These methods allow to infer structural information of a mono-crystalline material, such as its crystal orientation or structural defects, through the reflection or transmission of polychromatic X-ray beams. Laue diffraction methods are categorized according to the relative position of the X-ray source, the detector and the sample. The back- or side reflection method allows to determine defects on the surface of the sample material. However, the advent of mono-crystalline structures featuring more complex geometric shapes has rendered such methods partly inadequate for efficient and accurate quality control. As internal defects within the sample volume cannot be detected with this method. These drawbacks are overcome with the Transmission Laue technique, in which the detector is placed behind the crystal to record X-ray beams transmitted through it. In this work, after a brief introduction to Transmission Laue, we explore in detail the impact of detector choice on the performance and feasibility of the Transmission Laue method. To this end, a series of similar tests have been conducted on a classic CsI flat Panel and at the CSEM facilities in Zurich with a DECTRIS PILATUS 3 CdTe detector. A quantitative comparison of the efficiency of these detectors for this imaging modality is derived. Several parameters such as the sample thickness or the exposure time have been compared in order to evaluate the accuracy of the acquisition.

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