Effect of Geometry on Local Microstructure in Ti-6al-4v Fabricated by Laser Powder Bed Fusion

Abstract

Laser Powder Bed Fusion (L-PBF) is a unique technology that enables manufacturing geometrically complex metal alloys, including Ti-6Al-4V parts. The microstructure of Ti-6Al-4V is determined by localized thermal history, which is affected by not only the L-PBF process but also the geometry of the part. Understanding the microstructure at specific locations in complex geometries is of great importance in predicting the mechanical performance of Ti-6Al-4V parts. This work investigates the effects of geometric features on the local microstructure. Three geometries, namely, holes, overhangs, and penholders, were designed and used for this study. Three different laser powers, namely 150 W, 250 W, and 350 W were set to print those geometries. The use of lower laser power results in improved print quality. While the martensite phase dominates the bulk of the L-PBF Ti-6Al-4V parts, fine α+β lamellar structure can form at down-skin regions of printed horizontal holes and overhangs. Moreover, the direction of the columnar prime β grain can shift due to the directional heat dissipation. The local microstructural evolution after heat treatment is investigated as well.

Keywords: Additive manufacturing, Laser powder bed fusion, Ti-6Al-4V, Geometry