X-ray computed tomography (CT) is a nondestructive evaluation technique that may be used to image complex internal features without the line-of-sight restrictions inherent in conventional optical and contact (stylus) metrology instrumentation. However, scan artifacts, such as streaking, caused primarily by beam hardening and scatter, limit the accuracy of CT-based metrology. Reduction of these artifacts would improve the accuracy of information regarding material properties and dimensional metrology.
We developed additively manufactured Ti5553 titanium and 316L stainless steel measurement phantoms with integral lattice structures specifically to exhibit these artifacts. The phantoms were scanned by three CT systems and a scanning-probe coordinate measuring machine (CMM). Surfaces generated from uncorrected CT data exhibited "dimple" defects that are not present in the CMM measurement. Correction methods were developed in Livermore Tomography Tools software, and artifacts were successfully corrected. Our work can be applied to areas in which characterization of defects, dimensions, and surface texture using CT are critical.
Our study leveraged and supported Lawrence Livermore National Laboratory's core competencies in advanced materials and manufacturing. Our results provide critical improvements in additive manufacturing that, in turn, support the Laboratory's stockpile stewardship mission area.
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