Electrochemical machining of additively manufactured gamma-TiAl parts: post-processing technique to reduce surface roughness

Additive manufacturing (AM) is a promising method for the manufacturing of complex geometries. Electron beam melting (EBM) is one of the powder bed AM processes which is used for hard metals to produce near and net-shape parts. The most encountered drawback in the EBM process is the surface quality, which plays a critical role on service life of the parts, particularly under variable loads. Electrochemical machining (ECM) is a non-traditional machining method in which the workpiece can be machined regardless of its hardness. This research presents a post-processing method for AM parts and dissolution mechanism of gamma-TiAl alloys in order to improve the surface quality. For that purpose, Ti-48Al-2Cr-2Nb alloy is chosen and the sample parts are manufactured by EBM process. EBMed parts are machined using different ECM process parameters such as cathode material, feed rate, and electrolyte conductivity. Measurement results show that better surface roughness (S-a) values are obtained for the brass cathode. S-a values for the copper and brass cathodes are decreased from 63.80 to 1.8 mu m and 0.98 mu m, which corresponds to improvement rates of approximately 97% and 98.4%, respectively. Experimental results also showed that the chemical composition and microstructure of the hot isostatic pressed (HIPed) gamma-TiAl cause unexpected results for copper. Heterogonous distribution of aluminum in the built layer effects the MRR and surface roughness. Layer peaks are not removed efficiently at low electrolyte conductivity values and oxide layer formation is observed in the valley that caused high surface roughness. Brighter surface is observed at highest electrolyte conductivity due to the removed oxide layer. Surface texture is examined with scanning electron microscope (SEM). In addition, as the formation of oxide layers was prevented, micropores were detected on the surface.