Ultrafine eutectic Ti-Fe-based alloys processed by additive manufacturing - A new candidate for high temperature applications

The development of metals tailored to the metallurgical conditions of laser-based additive manufacturing is crucial to advance the maturity of these materials for their use in structural applications. While effort s in this regard are being carried out around the globe, the use of high strength eutectic alloys have, so far, received minor attention, although previous works showed that rapid solidification techniques can result in ultrafine microstructures with excellent mechanical performance, albeit for small sample sizes. In the present work, a eutectic Ti-32.5Fe alloy has been produced by laser powder bed fusion aiming at exploiting rapid solidification and the capability to produce bulk ultrafine microstructures provided by this processing technique. Process energy densities between 160 J/mm(3) and 180 J/mm(3) resulted in a dense and crack-free material with an oxygen content of similar to 0.45 wt.% in which a hierarchical microstructure is formed by pm-sized eta-Ti4Fe2Ox dendrites embedded in an ultrafine eutectic beta-Ti/TiFe matrix. The microstructure was studied three-dimensionally using near-field synchrotron ptychographic X-ray computed tomography with an actual spatial resolution down to 39 nm to analyse the morphology of the eutectic and dendritic structures as well as to quantify their mass density, size and distribution. Inter-lamellar spacings down to similar to 30-50 nm were achieved, revealing the potential of laser-based additive manufacturing to generate microstructures smaller than those obtained by classical rapid solidification techniques for bulk materials. The alloy was deformed at 600 degrees C under compressive loading up to a strain of similar to 30% without damage formation, resulting in a compressive yield stress of similar to 800 MPa. This study provides a first demonstration of the feasibility to produce eutectic Ti-Fe alloys with ultra fine microstructures by laser powder bed fusion that are suitable for structural applications at elevated temperature. (c) 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/ )