Corrosion behaviour of glow discharge nitrided titanium alloys

The aim of this work is the study of the corrosive behaviour of glow discharge nitrided Ti-6Al-4V alloy, using electrochemical techniques. Potentiodynamic polarisation and electrochemical impedance measurement show the excellent corrosive resistance of titanium alloy after thermochemical treatment, as well as different behaviour between the alloy before and after the nitriding treatment. Also, in very hostile environments, such as 5 wt.% HCl, where the titanium alloy is heavily corroded, the nitrided samples show good resistance. Nevertheless, 750 degreesC nitrided samples have worse behaviour than those treated at 900 degreesC. This is probably due to the lower corrosion resistance of the nitride epsilon present in the nitrided layer created at the lower temperature than the nitride 8, and the limited thickness of the modified layer obtained at this temperature. (C) 2002 Elsevier Science Ltd. All rights reserved.