Surface modification of titanium by a diffusional carbo-nitriding method Original Research Article

After heat-treating a titanium specimen at a temperature between 1388 and 1573 K in a graphite cup in an atmosphere of pure nitrogen, all the surfaces of the specimen were covered with a layer of titanium monocarbo-nitride, Ti(C, N), and a layer of nitrogen-rich α-titanium had formed under the Ti(C, N) layer. The thicknesses of those layers increased with increase in both temperature and time of the heat treatment in accordance with the parabolic law. The parabolic rate constants for the increases in thicknesses of the layers of the Ti(C, N) and α-titanium were described as k1=4.28×10−5 exp (−217000/RT) m2/s and k2=1.86×10−5 exp (−119000/RT) m2/s, respectively, using Arrhenius’ equation. Vickers hardness of the Ti(C, N) layer remained at approximately 2000 but that of the α-titanium layer gradually decreased from 1500 to 500, as the distance from the surface increased. The carbo-nitride-treated titanium exhibited high bending strength and excellent resistances in wear and corrosion compared with those of pure titanium.