Electrochemical dissolution behavior of TNM intermetallic in sodium nitrate solution

Abstract

TNM alloy is a new kind of lightweight and high temperature resistant material. Electrochemical machining (ECM) is an ideal manufacturing method for TNM alloy because of its high machining efficiency and good machining quality. In this work, the dissolution properties and surface passive film of TNM in NaNO3 solution are studied comprehensively. The passivation properties of the samples are tested using potentiodynamic, potentiostatic and CV curves. The results show that there are obvious passive and transpassive areas on the surface of TNM alloy, and the corrosion resistance of the passive film gradually increased with the test time from 0 to 7200 s. XPS and EIS indicate that the passive film mainly consists of Al2O3, TiO2, Nb2O5 and MoO3. Its structure is a bi-layer consisting of an inner layer with few pores and an outer layer with many pores. A corresponding schematic model is also proposed to characterize the interface structure between TNM alloy matrix and passive film. TNM alloy has a very high material removal rate according to the ηω-j curve. The dissolution morphology of TNM alloy is observed at various current densities. It is found that the surface dissolution morphology is very different under low and high current densities. The sample exhibits a loose lamellar microstructure with some isolated lamellar colonies at low current density, while the surface is quite smooth (about Ra 0.55 μm) when current density (j) > 20 A/cm2. Finally, the material dissolution process of TNM alloy at 2 and 25 A/cm2 is also presented.

Keywords

• Electrochemical dissolution behavior
• TNM alloy
• Surface passive film
• EIS
• XPS