Evaluation of polychromatic X-ray radiography defect detection limits in a sample fabricated from Hastelloy X by selective laser melting |
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| Affiliation: | 1. Department of Materials Engineering, Monash University, Wellington Road, Clayton, Melbourne, Victoria 3800, Australia;2. School of Physics, Monash University, Wellington Road, Clayton, Melbourne, Victoria 3800, Australia;1. Département Imagerie Simulation pour le Contrôle, CEA, LIST, Gif-sur-Yvette 91191, France;2. Department of Mechanical Engineering, University of Western Macedonia, Kozani 50100, Greece;3. Department of Electrical Engineering, Technological Educational Institute of Western Macedonia, Koila 50100, Greece;4. Département de Recherche en Electromagnétisme, Laboratoire des Signaux et Systèmes UMR8506, CNRS-SUPELEC-Université Paris Sud 11, 3 rue Joliot-Curie Gif-sur-Yvette 91192, France;1. Multi-Scale Additive Manufacturing Lab, University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canada;2. Department of Mechanical & Mechatronics Engineering, University of Waterloo, 200 University Ave W, Waterloo, ON, N2L 3G1, Canada;3. Siemens Canada Limited, 9505 Côte-de-Liesse, Montréal, Québec, H9P 1A5, Canada;1. School of Instrument and Electronics, North University of China, Taiyuan, 030051, China;2. School of Electrical and Electronic Engineering, The University of Manchester, Manchester, M13 9PL, UK;3. North China Institute of Aerospace Engineering, School of Electronic and Control Engineering, Langfang, 065000, China;4. Taiyuan Institute of Technology, Department of Electronic Engineering, Taiyuan, 030008, China |
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| Abstract: | Selective laser melting is a rapidly maturing additive manufacturing technology ideally suited to the net-shape fabrication of high value metallic components with complex shapes. However, if the processing conditions are poorly controlled, internal defects such as cracks or pores filled with metal powder may be present and impair the properties. As a result, a non-destructive defect detection method needs to be found that is suited to this application. In this work, a staircase sample was designed and fabricated from Hastelloy X by selective laser melting with step thicknesses ranging from 0.8 mm to 10 mm and with each step containing the same series of custom-made spherical, rod-shaped and coin-shaped defects arranged in different orientations and ranging from 0.2 mm up to 2 mm in size. The sample was exposed to various X-ray radiography testing and analysis methods. In particular, a theoretical and experimental evaluation of defect detection limits by polychromatic X-ray absorption radiography was performed based on the measurable contrast, which depends on both defect size and shape and slab thickness. The experimental data suggest that the minimum detectable contrast is about 1–2% when using X-rays with a very broad spectrum. This equates to a minimum detectable defect size of about 0.2 mm for a Hastelloy X slab thickness of <2 mm. The experimental findings are in good agreement with theoretical expectations. The theoretical framework provides a criterion for estimating contrast, which is useful for optimising the experimental conditions. Polychromatic X-ray absorption radiography represents a simple and effective non-destructive investigation technique. Methods for further improving the defect detection limits are also discussed and examples relative to computed tomography are reported. |
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| Keywords: | Non-destructive testing X-ray radiography Tomography Defect detection limit Selective laser melting |
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