RF Plasma Nitriding of Titanium.

RF plasma nitriding of titanium was carried out at different temperatures and electric potentials of the samples, at 1.0-1.3 Torr in mixtures of nitrogen and hydrogen gases. The addition of hydrogen to nitrogen increased the nitriding rate and the hardness of the nitrogen diffusion layer. Kinetic study indicated that nitriding behavior changed in the temperature range between 1000°C and 1100°C. It is considered that the ε phase, which has the effect of suppressing nitrogen diffusion, is not present in samples nitrided at 1100°C. The nitriding rate decreased in samples with a positively biased potential. It is therefore inescapable nitrogen ions exerted some effect on the nitriding rate in these experiments. The nitrogen diffusion layer formed by plasma nitriding was harder than that formed by thermal nitriding. Hence, the nitrogen concentration in the nitrided layer in the plasma nitriding must be higher than that in the thermal nitriding.