Processing, microstructures and mechanical response of a β-metastable Ti-14Mo alloy fabricated by Electron Beam Powder Bed Fusion

Abstract

Defect-tolerant materials are good candidates to be produced by additive manufacturing as parts often suffer from the presence of various kinds of defects: internal (pores) and especially surface defects (roughness). A β-metastable binary Ti-14Mo alloy exhibiting a TWIP effect with a composition adapted to take into account constraints of powder bed additive manufacturing processes was fabricated by electron powder bed fusion (E-PBF). The processing window was identified and dense samples with a relative density > 99.9% measured by X-ray computed tomography were fabricated. Microstructures were examined using metallography, X-ray diffraction, and electron microscopy. The mechanical properties were determined using monotonous and cyclic loading-unloading tensile testing. The as-built microstructure shows a two-phase α + β microstructure with a gradient in size of the α phase along the building direction. Post-fabrication heat treatment is therefore required to achieve a β-metastable microstructure. The peculiarities and similarities with other β-metastable binary Ti-Mo alloys fabricated by the more traditional cast and wrought processing route are highlighted. The possibility to tailor the mechanical response by low-temperature ageing via precipitation of the ωiso phase is also investigated. Such Ti-alloy could be used to improve the energy absorption capacity of architected materials for which the surface-to-volume ratio is very high and thus defect tolerance is of utmost importance.