Microwave plasma characteristics in steel nitriding process

We report the plasma parameters of a microwave discharge immersed in a magn etic field (ECR type) studied as a function of the type of gas used to indu ce the discharge. Plasma diagnostics included a Langmuir probe, an ion ener gy analyzer and an optical emission spectroscopy system. Results of the dia gnostics are discussed in connection with the influence of the plasma param eters on the nitriding of steels. Different H-2/N-2 mixtures were used to f orm the plasma and carry out the nitriding of AISI-316 stainless steel, wit h samples at the plasma floating potential, so that the energy of the ions hitting the sample surface depends on the difference between the plasma pot ential and the floating potential. Treatments were carried out in the low t emperature regime (similar to 450 degreesC), where the steel keeps its anti corrosive properties and its structure corresponds to the so-called expande d austenite according to our X-ray diffraction results. The highest surface hardness was obtained when a 60:40 (H-2/N-2) gas mixture was used, corresp onding to a 380% hardness increase for a 50-min treatment. (C) 2000 Elsevie r Science S.A. All rights reserved.