The effect of pulse width on the microstructure of d.c.-plasma-nitrided layers

Modern ion nitriding equipment are powered by pulsed sources in order to pr event arcing and overheating. In industrial applications, the pulse frequen cy is usually adjusted to set the working temperature. However, frequency v ariations may drastically affect the plasma species population, and consequ ently, the microstructure of the final nitrided layer. In this study, AISI- 409 steel was nitrided in a mixture of 20% N-2-80% H-2 using a d.c power so urce. The depth and microstructure of the nitrided layer were assessed as a function of the time that the voltage was off, t(off), in the range of 1-4 ms during a 10 ms pulse cycle. The results suggested that both the microst ructure and mechanical behavior of the nitrided layer were affected by t(of f). Long t(off) values imply a deleterious effect on the mechanical propert ies of the nitrided layers. (C) 1999 Elsevier Science S.A. All rights reser ved.