An investigation on the processing conditions of Ti-6Al-2Sn-4Zr-2Mo by electron beam powder bed fusion: Microstructure, defect distribution, mechanical properties and dimensional accuracy

Abstract

In comparison with Ti-6Al-4V, which is the most common titanium alloy, Ti-6Al-2Sn-4Zr-2Mo (Ti6242) is a crucial structural material with a maximum service temperature of 540 °C. One of the key applications of this alloy is in the hot sections of power generation systems, such as impeller. Because of its higher thermal resistance, the processability of this alloy through conventional manufacturing processes is challenging. For this reason, new manufacturing processes such as Additive Manufacturing (AM) could attract attention in producing components made of this alloy. Among the AM processes, laser powder bed fusion suffers from low productivity and high residual stresses, especially in bulk components. Hence, this work aims to investigate the processability of the Ti6242 complex geometry components through the Electron beam powder bed fusion (EB-PBF) process. A design of experiments approach is adopted to identify the best hatching conditions that produce a fully dense material. The contour strategy is also optimised to obtain the lowest surface roughness. The influence of processing conditions on the final density, microstructure and defect content is investigated using different techniques, including X-Ray computer tomography (CT) analysis. With this scope, simple squared parallelepiped samples are produced. Then, selected optimum process conditions are adapted to produce more complex geometries, such as cylindrical tensile specimens and an impeller, which requires a dynamical control of the melt pool according to the section to be melted. The density and the accuracy of the impeller are evaluated using X-Ray computer tomography scanning.