Spherical pores as 'microstructural informants': Understanding compositional, thermal, and mechanical gyrations in additively manufactured Ti-6Al-4V

Detailed analysis of defects such as spherical porosity can act as informants, providing some information regarding the complex and often hidden physics associated with additive manufacturing. Variation in the presence and nature of these defects can shed new insights into the AM process. In this paper, the compositional, crystallographic, microstructural, and morphological characteristics surrounding gas pores in Electron Beam Melted Ti-6Al-4V have been assessed and correlated with different scanning strategies (raster and two point melting ones, Dehoff and random). The large spherical pores (>25 mu m), exclusively present in raster scan, exhibit perturbations normal to the vertical sidewalls of the pores that are likely the result of elastic instabilities resulting from chemical and crystallographic variations and initiated by vertical compression caused by thermal stresses related to the cyclic process - effectively a form of microbuckling. Electron backscatter diffraction maps support the theory that these perturbations occur at elevated temperatures and prior to the final solid-solid phase transformation. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd.

Automated summary

This study investigates the characteristics and formation mechanisms of gas pores in additive manufacturing, specifically in Electron Beam Melted Ti-6Al-4V. The presence of large spherical pores exclusively in raster scan suggests perturbations caused by elastic instabilities from chemical and crystallographic variations. The findings provide insights into the physics of defects in the AM process.