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X-Ray Computed Tomography for Nondestructive Evaluation of Advanced Structural Ceramics

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X-Ray Computed Tomography for Nondestructive Evaluation of Advanced Structural Ceramics ANL-87-52 hnoloqy • Materials ; i Mater.Ji - .niponenis T(H;.'niv).v>gy Division Matenr!f :^.nd Comoortcrtts n Materials and Components X-Ray Computed Tomography for Technology Division Materials and Components Nondestructive Evaluation of Technology Division Advanced Structural Ceramics Materials and Components Technology Division M^ inU Conipoiiedis lechnology Division by William A. Ellingson and Materials and Comp'^f^*»nts Michael W. Vannier Technology r i Materials and Components Technology r n Materials and Components Technology Division Materials and Components Technology Division Materia Components 1 ecnnology Division Materials and Components Technology Division j-Tf?f*ni Tf> r»"' Materials and Components RET • FILE Technology Division Materials and Components •,•> Technology Division Materials and Components Technology Division Argonne National Laboratory, Argonne, Illinois 60439 n operated by The University ot Chicago tor the United States Department ot Energy under Contract W-31-109-Eng-38 Materials and Components Technology D -. Materials and Componenis Technology Division Materials and Components Technology Division Materials and Components Technoloav Division Argonne National Laboratory, with facilities in the states of Illinois and Idaho, is owned by the United States govemment, and operated by The University of Chicago under the provisions of a contract with the Department of Energy. DISCLAIMER- This report was prepared as an account of work sponsored by an agency of the United States Govemment. Neither the United States Govemment nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or pro­ cess disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not nec­ essarily constitute or imply its endorsement, recommendation, or favoring by the United States Govemment or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Govemment or any agency thereof. This report has been reproduced from the best available copy. Available from the National Technical Information Service NTIS Energy Distribution Center P.O. Box 1300 Oak Ridge, TN 37831 Price: Printed Copy A04 Microfiche AOl Distribution Categories: Heat Engines (UC-111) and Coal-Based Instrumentation (UC-115) ANL-87-52 ARGONNE NATIONAL LABORATORY 9700 South Cass Avenue Argonne, Illinois 60439 X-RAY COMPUTED TOMOGRAPHY FOR NONDESTRUCTIVE EVALUATION OF ADVANCED STRUCTURAL CERAMICS by Williaffl A. Ellingson and Michael U. Vannier* Materials and Components Technology Division September 1988 Prepared for the U.S. Department of Energy, Office of Fossil Energy, Advanced Research and Technology Materials Development Fossil Energy Materials Program (FVP 49640) and the U.S. Department of Energy, Assistant Secretary for Conservation and Renewable Energy, Office of Transportation Systems, as part of the Ceramic Technology for Advanced Heat Engines Project of the Advanced Materials Development Program (Contract ACK-85234). *Malllnckrodt Institute of Radiology/Washington University, St. Louis, MO. TABLE OF CONTENTS Page ABSTRACT 1 I. INTRODUCTION 1 1.1. System Architecture 2 1.2. Technical Considerations 5 1.2.1. X-Ray-induced Artifacts 5 1.2.2. Mechanical and Thermal Stability of Components 6 1.2.3. Detectors 6 II. CONSIDERATIONS FOR CERAMIC MATERIALS 8 III. CORRECTION FOR BEAM HARDENING 10 IV. EXPERIMENTAL RESULTS 15 4.1. Verification of Optimum Energy 15 4.2. Inclusions 16 4.3. Turbocharger Rotors 29 4.4. Ceramic-Ceramic Composites 31 V. SUMMARY AND CONCLUSIONS 41 ACKNOWLEDGMENTS 41 REFERENCES 42 APPENDIX A: EFFECTIVE ATOMIC NUMBER 45 APPENDIX B: PHOTON SOURCES 48 ill LIST OF FIGURES No. Title Page 1. Schematic Diagram of X-Ray Computed Tomography System 3 2. Source-Detector Configurations for CT Scanners 4 3. Schematic Diagram of an Ionization Multidetector 7 4. The Basis-Material Plane 12 5. Processing Scheme for Dual-kVp Data Evaluation 13 6. Illustration of the Dual-Energy Principle and Resulting CT Images 14 7. Theoretical Optimum Incident Photon Energy as a Function of Energy for Green and Dense SijN^ Specimens of Various Thicknesses 16 8. Set of Equivalent Monoenergetic-Photon Images of a 105-mm- diam Bottle of Freon TF 17 9. Linear Attenuation Coefficient of Green and Dense SioN/ and a Potential Calibration Fluid, Freon TF 19 10. Experimentally Obtained Optimum Incident Photon Energy for a 51-mm-diam Green-State SioN^ Sample 19 11. Experimentally Obtained Optimum Incident Photon Energy for a 105-mm-diam Freon TF Sample 20 12. Schematic of SijN^ Test Specimen Used in CT Studies 20 13. Schematic Diagram of Array of High-Density Seeded Inclu­ sions in Green-State Specimen Shown in Fig. 12 20 14. Computed Scan Projection Radiograph of Si^N^ Test Specimen 21 15. Same Image as Fig. 14 but with Window at 350 and Center at -37 HU 22 16. Series of CT Images of Green-State Si3N^ Test Specimen with Seeded High-Density Inclusions 23 17. Series of CT Images of Same Specimen Shown in Fig. 16, with 1-mm Slice Thickness 24 18. CT Image of Same Specimen Shown in Figs. 16 and 17, with 2-mm Slice Thickness 25 IV LIST OF FIGURES (continued) tifi. lilifi Page 19. Densitometer Traces of CT Image at Table Position 42, along Lines through 1000-/im Fe Markers, Fe Test Inclusions, SiC Test Inclusions, and W Test Inclusions 27 20. Densitometer Traces of CT Images at Table Positions 42 and 43; Windows and Center Positions are Different from those of Fig. 19 28 21. Green-State Turbocharger Rotor Used in Experimental Dual- Energy CT Scan Tests 29 22. Close-up Photograph of Turbocharger Rotor, Showing Circum­ ferential Surface-breaking Crack 29 23. Axial CT Image of Rotor Shown in Fig. 22, Obtained with the Dual-Energy Beam-hardening Correction 30 24. Transaxial CT Image of Same Rotor, Taken Through the Vanes 30 25. Transaxial CT Image of Same Rotor, Taken Upstream of the Vanes 31 26. CT Image of Same Rotor Section Seen in Fig. 25, with Densitometer Trace 31 27. Photograph of Three of the CVI SiC Specimens of Set 2 after Infiltration and Removal from Holder 32 28. Photograph of Two of the CVI SiC Specimens of Set 2, Still in Holders 33 29. Metallographic Polished Section of Plain-Weave Specimen CVI - 57 34 30. CT Images of Specimen CVI-57 35 31. Metallographic Polished Section of Chopped-Fiber Specimen CVI-64 36 32. CT Image of Specimen CVI-64 36 33. Photomicrograph of Satin-Weave Specimen CVI-65 37 34. CT Image of Specimen CVI-65 37 35. Digital Radiographic Image Showing Arrangement of CVI Specimens on CT Scanner Table 38 36. CT Image of Unlnflltrated Plain-Weave Preform in Holder .. 39 LIST OF FIGURES (continued) No. Title Pass 37. CT Image of Infiltrated Plain-Weave Specimen 130-4 . 39 38. CT Image of More Completely Infiltrated Plain-Weave Specimen 127-1 in Holder 39 39. CT Image of Infiltrated Satin-Weave Specimen 130-2 40 40. CT Image of Chopped-Fiber Specimen 130-3 Taken at the Interface Between the Known Low-Density Region and the Higher Density Region 40 41. CT Image of Specimen Shown in Fig. 36, Obtained with CT Scanner in Dual-Energy Configuration at 85 and 125 kVp Head Voltages 40 42. Portion of CT Image Shown in Fig. 41, Enlarged to Show More Detail of the Composite Structure 41 LIST OF TABLES I. Common Processing Operations for Advanced Ceramics 9 II. Comparison Between Inclusion and Voxel Volume for Various Inclusion Sizes 25 III. CVI Specimen Set 1 32 IV. CVI Specimen Set 2 32 VI X-RAY COMPUTED TOMOGRAPHY FOR NONDESTRUCTIVE EVALUATION OF ADVANCED STRUCTURAL CERAMICS William A. Ellingson and Michael W. Vannier ABSTRACT This report characterizes the current status of X-ray computed tomography (CT) as applied to the nondestructive evalua­ tion of ceramic materials. The principal advantages of X-ray CT scanning are two. The first is the capability to produce high- contrast, geometrically accurate digital pictures (images) of slices through an object with a reasonably high spatial reso­ lution. The second is that these slice images are not influenced to any significant degree by overlap or by structures outside of the plane of section (the tomographlcally imaged plane). Conven­ tional radiography offers neither of these advantages. I. INTRODUCTION Computed tomography (CT) is a well-established imaging modality used in medical diagnostic radiology. Industrial applications have been described in the nondestructive testing literature for the past 10 years. The tech­ nology, especially for ceramic materials, is still in its infancy, and CT is thought of primarily as a research technique, but with important potential for future improvements. CT scanning is, fundamentally, a method for producing spatial maps of the local X-ray attenuation within a slice through an object. Generally speaking, slice imaging is synonymous with tomography. It is possible to form slice images of an object by holding the object stationary and moving a source and detector about a point in the object which lies between them. Part of the object will be in focus on the resulting image and part will be blurred. If one-dimensional detectors are used and sufficient projections are available, the influence of blurring from over- and underlying struc­ tures may be removed mathematically. The mathematical basis for CT scanning is reconstruction from pro­ jections. In much the same fashion that the temperature distribution within a flame or the distribution of stars within a galaxy may be computed from external projections, the spatial distribution of X-ray attenuation within an object may be reconstructed by obtaining samples of line integrals through the object at different source-detector orientations (1-dimensional projections) followed by a suitable computational step.
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