Nitriding at low temperature

This paper reports advances in the use of low-pressure rf plasmas for nitri ding with an emphasis on treatments at temperatures of 250-450 degreesC; i. e. well below those used by more conventional methods. The treatment of aus tenitic stainless steel AISI-316 was chosen to represent the efficacy of su ch plasmas for nitriding over a wide temperature range, producing thicker n itrogen-rich layers at low temperature than more conventional methods in th e same process time. This is due to a lower activation energy. Application of high-voltage pulses to the workpiece (plasma-immersion ion implantation, PI3) increases the thickness of the nitrogen-rich layer but does not signi ficantly alter the activation energy. Other aspects of the process investig ated include the role of hydrogen, various regimes of plasma-based cleaning , process gas purity and the variation of workpiece bias, from zero up to t he 10s of kV characteristic of PI3. (C) 2000 Elsevier Science B.V. All righ ts reserved.