Surface characteristics of additively manufactured γ-TiAl intermetallic alloys post-processed by electrochemical machining

Abstract

Electron beam melting (EBM) process is the most preferable powder bed fusion process for high melting point alloys. γ-TiAl alloys are intermetallic chemical compounds, which are lightweight and resistant to oxidation and heat, and have low ductility as well. EBM is the best manufacturing process for such alloys to produce aerospace parts, but poor surface quality is the main drawback of this process. Thus, surface post-processing is needed after the EBM process. This study presents the surface characteristics of EBM γ-TiAl alloy surfaces post-processed by electrochemical machining (ECM). The surfaces were ECM and the surface roughness values (Sa, Sq and Sz) have been reduced significantly. The mean reduction values of the experiments are 98.6 %, 98.5 % and 95.3 % for Sa, Sq and Sz, respectively. Additionally, it is observed that the surface roughness is inversely proportional to the electrolyte conductivity up to a limit value (115 mS/cm), and after that the roughness increases via the stray current transition. Sq values decrease with the increased feed rate via the increased current density. However, an increase in feed rate negatively affects the Sku values, which statistically describe the sharpness or spread of surface roughness. Also, XRD results showed that Ti2AlN layer is formed on the surface via the HIP operation. This layer inhibits the electrochemical dissolution of γ-TiAl alloy and caused surface defects.