Characterization and electrochemical behavior of a multilayer-structured Ti–N layer produced by plasma nitriding of electron beam melting TC4 alloy in Hank's solution

Abstract

In this work, electron beam melting (EBM) titanium alloy were strengthened by carrying out a hollow cathodic plasma source nitriding treatment. The EBM-TC4 alloys were nitrided at 500 °C for 1, 3, and 5 h in an NH3 atmosphere. X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy was used to evaluate the microstructure and surface morphology of the samples. The nitrided layers formed on the EBM-TC4 alloy were identified as TiN, Ti2N, and nitrogen-stabilized α(N)–Ti phases. Potentiodynamic polarization and electrochemical impedance spectroscopy measurements were carried out to evaluate the electrochemical behavior of the samples in Hank's balanced salt solution. The relationship between the corrosion resistance of the nitrided layer and its microstructure was explored. Thus, the improved properties of the nitrided alloys can be attributed to the formation of a Ti–N layer composed of an outermost nanocrystalline/amorphous TiN layer and a crystalline TiN sub-layer on the top of the Ti2N crystal layer. The novel Ti–N layer structure with improved corrosion resistance provides broad opportunities for the application of commercial Ti alloys and improving their durability.