Corrosion and wear-corrosion behavior of the nitrided layer on selective laser melting fabricated TC4 alloy by hollow cathodic plasma source nitriding

Selective laser melting (SLM) fabricated titanium alloys have attracted growing interest due to their ability to produce complex shapes and custom-designed components in a rapid, low-cost and material-efficient manner. However, the low hardness and poor wear resistance of titanium alloy confine its further industrial application. In this work, SLM-TC4 alloys were nitrided using hollow-cathode plasma technology. The phase structures, morphologies, and compositions of different samples were characterized using X-ray diffraction, transmission electron microscopy, atomic force microscopy, scanning electron microscopy, and energy dispersive x-ray spectroscopy. The phases formed on the surface of the nitrided samples were primarily TiN, Ti 2 N, and α-Ti(N). The outermost surface of the TiN layer consisted of nanocrystalline TiN, with the subsurface layer being crystalline TiN. Potentio-dynamic polarization and electrochemical impedance spectroscopy were used to assess the electrochemical behavior of the nitrided samples, and friction experiments were conducted in the natural seawater of China's Yellow Sea. The TiN layer played a crucial role in hindering corrosion and substantially reduced the corrosion rate of the nitrided samples. The wear mechanism of the SLM-TC4 substrate was severe adhesive wear, whereas that of the nitrided samples was abrasive wear in the natural seawater.