Effect of X-ray Computed Tomography Scan Noise on Observation of Internal Defects in a Blade Part Fabricated by Wire Arc Additive Manufacturing

The application of additive manufacturing to the fabrication process of metal parts has the potential to solve some of the problems that have existed in the industry for a long time. On the other hand, it is necessary to guarantee sufficient quality of the fabricated parts. One of the causes of functional degradation of parts fabricated by additive manufacturing is the presence of internal defects such as blowholes. In the case of turbomachinery blade parts, damage to the parts caused by internal defects may result in a noticeable loss of machine performance; therefore, it is necessary to accumulate a great deal of knowledge and make appropriate judgments. For this reason, there is an active discussion on the integrity of parts. A suitable method of additive manufacturing for large parts is wire arc additive manufacturing (WAAM). In addition, X-ray Computed Tomography (CT) scans are often used for the observation of internal defects in metal additively fabricated parts.
The purpose of this study is to clarify the effect of artifacts, which are noise from X-ray CT scans, for the proper evaluation of internal defects in parts fabricated by WAAM. An axial-flow impeller made of general-purpose stainless steel, fabricated by WAAM and machining, was used as a test model. The blades of this impeller were observed for internal defects by X-ray CT scanning. Suitable imaging results and imaging results affected by artifacts were obtained by changing the imaging conditions. These results were used to consider the effects of artifacts on the imaging results. In conclusion, it was shown that artifacts may cause a misidentification of internal defects in parts fabricated by WAAM.