Systematic exploration of the L-PBF processing behavior and resulting properties of β-stabilized Ti-alloys prepared by in-situ alloy formation

Aim of this work is to gain a comprehensive understanding of the effects of an increasing β-phase stability of Ti-alloys on the L-PBF processing behavior. For this purpose, seven different Ti-alloys with an increasing concentration of the β-phase stabilizing elements Fe and V were prepared by L-PBF and in-situ alloy formation. The Molybdenum equivalent (Mo_eq) of the examined alloys, as a measure of β-phase stability, was varied systematically between −3.3 and 25. It is shown that a homogeneous distribution of elements is achievable by in-situ alloying. The experiments prove that the investigated alloys can be processed by a single L-PBF parameter set with high relative density above 99.8%. This finding is substantiated by calculated thermo-physical material properties and an analytical model. To understand the underlying metallurgical effects governing the L-PBF results, the samples were investigated extensively by EDS, EBSD, XRD, light microscopy and compression tests. The β-phase fraction varies in dependence of the Mo_eq between 0% and 99%. Because of rapid solidification inherent in L-PBF a Mo_eq of 10 is sufficient to receive more than 90% β-phase. The same amount of β-phase after furnace cooling was only observed in alloys with Mo_eq of 20 or more. While all alloy compositions can be processed with high relative density of over 99.8%, alloys with a Mo_eq between 15 and 20 show a brittle material behavior in as-built state, resulting in cracking during L-PBF. This behavior is attributed to the formation of ω-phase during L-PBF. In contrast, the highest β-stabilized alloy with a nominal Mo_eq of 25 exhibits a very high ductility with a fracture strain exceeding 50%.