Review of high energy x-ray computed tomography for non-destructive dimensional metrology of large metallic advanced manufactured components

Abstract

Advanced manufacturing technologies, led by additive manufacturing, have undergone significant growth in recent years. These technologies enable engineers to design parts with reduced weight while maintaining structural and functional integrity. In particular, metal additive manufacturing parts are increasingly used in application areas such as aerospace, where a failure of a mission-critical part can have dire safety consequences. Therefore, the quality of these components is extremely important. A critical aspect of quality control is dimensional evaluation, where measurements provide quantitative results that are traceable to the standard unit of length, the metre. Dimensional measurements allow designers, manufacturers and users to check product conformity against engineering drawings and enable the same quality standard to be used across the supply chain nationally and internationally. However, there is a lack of development of measurement techniques that provide non-destructive dimensional measurements beyond common non-destructive evaluation focused on defect detection. X-ray computed tomography (XCT) technology has great potential to be used as a non-destructive dimensional evaluation technology. However, technology development is behind the demand and growth for advanced manufactured parts. Both the size and the value of advanced manufactured parts have grown significantly in recent years, leading to new requirements of dimensional measurement technologies. This paper is a cross-disciplinary review of state-of-the-art non-destructive dimensional measuring techniques relevant to advanced manufacturing of metallic parts at larger length scales, especially the use of high energy XCT with source energy of greater than 400 kV to address the need in measuring large advanced manufactured parts. Technologies considered as potential high energy x-ray generators include both conventional x-ray tubes, linear accelerators, and alternative technologies such as inverse Compton scattering sources, synchrotron sources and laser-driven plasma sources. Their technology advances and challenges are elaborated on. The paper also outlines the development of XCT for dimensional metrology and future needs.

Effects of Interfacial Electron Transport on Field Electron Emission from Carbon Nanotube Paste Emitters

“…Because the field emission (FE) source is based on a physical mechanism, in which electrons are quantum mechanically tunneled by the applied voltage, it has superior advantages with fast and accurate current controls compared to thermionic emission. − Recently, studies have been actively performed on the FE source to improve the performance of its X-ray applications, such as medical diagnosis and industrial inspection. − Among these studies, the main theme is to maximize the FE current because the insufficiency of the emission current limits the applicability for the X-ray devices that require high dose like radiography and computed tomography for medical and in-line inspection for industrial applications. , In terms of high emission current, carbon nanotube (CNT) is suitable as a material for the field emitter due to its high electrical and thermal conductivities, great mechanical strength, and high aspect ratio, and it is being actively studied at present. − Many researchers have focused on intrinsic parameters, including the work function and the aspect ratio of CNT emitters to improve the emission efficiency. − However, the extrinsic parameters of emitters that affect the FE property should be considered as well as intrinsic ones; extrinsic parameters include an adhesion property of the CNT emitters onto a cathode substrate and an electron transport property from the cathode substrates to emission sites.…”

The realisation of fast X-ray computed tomography using a limited number of projection images for dimensional metrology

“…X-ray computed tomography (XCT) has experienced rapid growth in recent years due to the significant demands of non-destructive evaluation (NDE) of advanced manufacturing, led by additive manufacturing [1][2][3]. The applications initially focused on imaging internal defects, such as pores and cracks.…”

Direct fabrication of pixelated detector arrays for high-energy x-ray imaging via additive manufacturing

“…With the increased use of additive manufacturing in industries such as aerospace, there is a need to inspect complex metal objects for their structural and functional integrity. Non-destructive quality assurance via high-energy x-ray imaging is limited by the poor efficiency of the commercial Gadox screens [5,6]. Amorphous silicon arrays with structured scintillators such as patterned Gd2O2S:Tb phosphor screens and GdAlO3-αAl2O3 fiber arrays have been explored, with the goal of improving resolution and efficiency [7][8][9].…”