Investigation on electrochemical characteristics of forged Ti-48Al-2Cr-2Nb in NaNO3 solution for its application on the manufacture of aero-engine blades

Electrochemical machining (ECM) has great advantages for the manufacture of difficult-to-cut gamma-TiAl alloys considering its many inherent advantages over traditional cutting techniques. In this study, the ECM characteristics of a new forged Ti-48Al-2Cr-2Nb (TiAl 4822) intermetallic with alpha and gamma phases were investigated in NaNO3 solution. The polarization characteristics of the sample were studied by potentiodynamic and potentiostatic polarization tests. The results show that the alloy has typical active, passive, and transpassive regions, and the compactness and corrosion resistance of passive film are getting better and better with the increase of test time at passive potential. The XPS test revealed that the main components of the passive film are titanium dioxide and aluminum oxide. Furthermore, the alloy exhibits high material removal rates that remain almost constant in the range of current density less than 50 A/cm(2). Moreover, the dissolution mechanism of TiAl 4822 alloy was also revealed through the dissolution morphology, elemental composition, surface roughness, and intergranular corrosion at different current densities. The sample shows a loose lamellar dissolution morphology and is very rough at low current density. The sample exhibits a very flat surface at high current density, but many micro-bulges with high content of Cr element on the dissolved surface. Finally, several forged TiAl 4822 alloy blades were successfully fabricated with an average surface roughness of Ra 0.55 mu m. It proves that ECM can obtain high surface quality and high material removal rate of forged TiAl 4822 alloy for complex structural components in aero-engines.