| Abstract Scope |
The Additive Manufacturing of metals through methods such as Laser Powder Bed Fusion is a hot topic each in academic research and industrial implementation. With the promise of producing complex parts out of a wide range of materials, advancements in each the materials, process, and post-processing technologies involved continue to be necessary. As these advancements progress, methods for quality control and critical evaluation of the produced materials and structures are each necessary. Seeking to identify and characterize defects in LPBF produced material, state of the art nondestructive evaluation (NDE) and microscopy techniques must be leveraged cooperatively. Micro CT is commonly used for three-dimensional reconstructions of structures and defects in powder bed applications. However, noted limitations for the detection of near planar defects by this process prompt the implementation of other techniques, such as ultrasonic testing (UT). Therefore, micro resolution ultrasonic imaging is considered as a NDE method to better identify these types of defects.
This work presents a direct comparison of Micro CT and micro resolution ultrasonic imaging for LPBF materials. Common defects such as porosity, lack of fusion, and cracking are analyzed, as well as intentionally placed cavities of varying shapes and scales. Special attention is paid to the design, slicing, and fabrication of these intentional defects to represent features that may be present in LPBF components each intentionally and unintentionally. Both NDE processes are evaluated upon their ability to detect and characterize each type of defect, with further validation provided by metallographic characterization. Additionally, aspects such as material, surface roughness, entrapped powder, and part geometry are analyzed to provide comprehensive comparison between these two processes. Finally, this analysis and direct comparison is complimented by a review of state-of-the-art advancements currently being made for each technology.
As a result of this work, the practice and advancement of LPBF may be better informed of available methods of NDE. While quality control of components intended to enter service is crucial, NDE methods must be deployed in an informed and intentional manner to fully capture the impact of changes to process, material, and post processing on LPBF produced materials. |