Microstructure, defects and mechanical behavior of beta-type titanium porous structures manufactured by electron beam melting and selective laser melting

This study investigates the differences in the microstructure, defects and mechanical behavior of porous structures from a beta-type Ti-24Nb-4Zr-8Sn manufactured by electron beam melting (EBM) and selective laser melting (SLM). The phases, size and shape of melt pool, volume and distribution of defects are analyzed and correlated to the compressive mechanical and fatigue properties. Due to different powder bed temperatures, the microstructure of EBM and SLM samples consists of alpha+beta phases and a single phase, respectively. The faster cooling rate during SLM promotes the formation of fine beta dendrites, which leads to a higher compressive strength (50 +/- 0.9 MPa) and lower Young's Modulus (0.95 +/- 0.05 GPa) in comparison to the EBM parts (45 +/- 1.1 MPa and 1.34 +/- 0.04 GPa respectively). The large defects present within solid strut are likely a result of tin vaporization. The tin vapor is more easily trapped during the SLM process due to a smaller laser spot size and a faster cooling rate. This results in a 10 times increase in the number of defects. These defects have a limited influence on both the static properties and low stresses level fatigue strength, but it causes a reduced and variable fatigue life at high stresses level. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.