A Perspective of The Needs and Opportunities for Coupling Materials Science and Nondestructive Evaluation for Metals-Based Additive Manufacturing

Abstract

This paper presents a perspective of the needs and opportunities associated with the multidisciplinary problem of nondestructive evaluation (NDE) of additive manufacturing (AM). Recognizing the multidisciplinary nature of the problem, as well as the need to bridge knowledge between the different communities, the paper is structured to provide brief backgrounds and details relevant to both communities, as well as present an assessment of the state of the art. This paper, in some respects, is meant to be a primer of the different landscapes, as well as a catalyst for making future connections. At the end, it will be clear that there is much more work to be done, but that the work that is ongoing is exciting, and the potential to exploit NDE techniques for metals-based AM is very high.

The use of defects and compositional variations to elucidate physical phenomena in electron beam melted Ti-6Al-4V across scan strategies

“…There are several different forms of porosity observed in AM samples, including but not limited to spherical porosity, keyhole porosity, acicular porosity, porosity due to balling effects, delamination porosity, and lack-of-fusion porosity [8,9,35,58,[76][77][78]. Several of these types have significant overlap in their definitions or can be considered a subcategory of another type.…”

“…These secondary characteristics help distinguish between the various mechanisms of formation used to create pores and provide details about local thermal history and the physical phenomena that take place during a build. These characteristics include partially melted powder particles or reformed spherical shapes as a result of balling; cracking; humping; microstructural features; spattered particles; and irregular geometries, among many others [8,9,35,58,[76][77][78]. This chapter presents observations from different types of defects and interprets their salient characteristics to reveal information about the physical mechanisms that are operating in electron beam melted (EBM) powder-bed AM Ti-6Al-4V parts.…”

“…These bands appear flatter and more uniform than those observed surrounding pores and defects, and fewer ripples (or turbulence) are observed, giving insights into the interactions of defects and bands. The observation of extended compositional fluctuations around pores is novel and may provide new methods of identifying and interpreting porosity using nondestructive evaluation techniques [76,[150][151][152], as the volume of distinctively different material is larger than the pore. However, the insight is not unexpected: LOF pores are formed while layers are still molten and interact as objects with the fluid flow of the melt pools (somewhat equivalent to solid, unmelted particles).…”