Investigation of parameters of inductively coupled plasma and its use in steel nitriding

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Parameters of inductively coupled plasma (ICP) discharges in a mixture of gases N₂, H₂, and Ar at a total pressure of 1.5 × 10^–3 mbar and a partial pressure ratio N₂: H₂: Ar = 2: 12: 1 are discussed. The plasma properties are analyzed using Langmuir probes and optical emission spectroscopy. The ICP discharge is used for the nitriding of specimens made of Russian grade 30ChGSA structural steel. The nitriding experiments are performed at different bias voltages V_b in the range of–200 V to +100 V with respect to the walls of the discharge chamber. The surface hardness of the treated specimens depends substantially on the bias voltage, being much higher than the initial value in all cases. The obtained results demonstrate the possibility of increasing the surface hardness up to 1000 HV (4–5 times the initial values) at the bias voltage equal to the floating potential.