A study on the microstructure and mechanical properties of the Ti-6Al-2Sn-4Zr-6Mo alloy produced via Laser Powder Bed Fusion

Abstract

• The LPBF Ti6246 microstructure is mainly composed of α” orthorhombic martensite. • The martensite provides low tensile strength and hardness but rather high ductility. • The microstructural and mechanical properties are related to the process parameters. • The yield strength can be markedly increased via sub-β annealing. Laser Powder Bed Fusion (LPBF) is an additive manufacturing technology which has been the subject of thorough research and successfully adopted in several industrial sectors. Among all the processable classes of materials, titanium alloys are especially interesting due to their favourable combination of mechanical properties and corrosion resistance. Most of the literature focuses on Ti-6Al-4V, although there are other alloys which are widely applied in fields that can benefit from the advantages of LPBF techniques, such as Ti-6Al-2Sn-4Zr-6Mo, thus far not investigated for this technology. This alloy is generally preferred to Ti-6Al-4V for the production of some components in the aerospace industry, mostly due to its superior strength. In this work, the most suitable process window for this alloy was investigated. Samples produced with two different combinations of process parameters, located in the selected process window, were then thoroughly studied in order to assess the effect of building conditions on the microstructure, phases and mechanical properties of the as-built and heat-treated material. To do so, an X-ray diffraction analysis was conducted with the aim of determining the phase composition and lattice parameters. Moreover, microstructural features, such as α” needles and α lath widths, were analysed in order to correlate the thermal history of the process to the final microstructure of the specimens. Furthermore, the hardness and the tensile properties of the alloy processed by LPBF were quantified and compared with the data available in the literature relative to conventional manufacturing technologies.