Active Screen Plasma Nitriding of Titanium Alloy Using Titanium Double Screen

The low hardness and poor tribological performance of titanium alloys restrict their wide applications in automotive fields. Nitriding is widely used to improve tribological properties, wear resistance, and corrosion resistance of steel and titanium alloys. Plasma nitriding is becoming increasingly popular because of its high nitrogen potential, short treatment time, and low environmental impact. Recently, considerable interest has been devoted to alternative nitriding methods such as active screen plasma nitriding (ASPN). In this study, a Ti-6Al-4V titanium alloy was nitrided by ASPN using a titanium double screen in order to investigate the effect of applying the double screen on the microstructure of the nitriding layer. The Ti-6Al-4V sample was placed on the sample stage in a cathodic potential. A titanium double screen was mounted on the cathodic stage around the sample stage. The sample was treated for 1-25 hours at 600oC under 200 Pa in 75% N2 + 25% H2 atmosphere. After nitriding, glow discharge optical emission spectroscopy (GD-OES) revealed that the thickness of the nitriding layer composed of TiN tended to increase with increasing the nitriding time. The Vickers microhardness of the sample surface nitrided for 25 hours reached approximately 1300 HV. Ball-on-disk wear test revealed that a wear loss of nitrided sample considerably decreased than that of untreated sample.