Hydrogen embrittlement resistance of Ni-Ti alloy cathode in a mixed solution of C12H25SO4Na and NaNO3 for electrochemical machining

Electrochemical machining (ECM) is one of the mainstream processes in the manufacture of aero-engine components. The tool cathode, an important carrier for ECM, is often in contact with hydrogen from the process. The hydrogen may interact with the cathode material and lead to hydrogen embrittlement of the cathode. In this paper, a mixture of NaNO3 and C12H25SO4Na was used as an electrolyte to improve the hydrogen embrittlement resistance of the Ni-Ti alloy cathode. The addition of C12H25SO4Na did not affect the normal dissolution of the material as demonstrated by electrochemical tests and experiments. Using scanning electron microscopy, energy disperses spectrometer and microhardness tester, it was elucidated that the surface morphology of Ni-Ti alloy cathodes changed from pitting to microcracking and the mechanical properties changed from ductile to brittle during the process of hydrogen embrittlement. It was also demonstrated that the addition of C12H25SO4Na could retard the hydrogen embrittlement process and improve the hydrogen embrittlement resistance of the cathode. Through in-situ observation experiments, the mechanism of increasing C12H25SO4Na in NaNO3 solution to improve the anti-hydrogen embrittlement performance of the cathode was revealed, which reduced the interfacial tension between the two phases, resulting in fewer bubbles adsorbed on the cathode surface and less time for bubbles to stay on the cathode surface. Finally, a qualitative model for the inhibition of hydrogen embrittlement by C12H25SO4Na was developed.