Plasma-Assisted Nitriding in Low-Frequency Inductively Coupled Plasma Enhanced with Ferromagnetic Cores

An experimental investigation of plasma-assisted nitriding of austenitic stainless steel AISI 321 in a low-pressure (7 Pa), low-frequency (50–100 kHz) nitrogen inductively coupled plasma enhanced with ferromagnetic cores has been performed at the temperatures of 470–625 °C, sample biases of ‒500–‒750 V, current densities on the sample surface of 1.2–3.3 mA/cm2 and nitriding times of 20 and 60 min. It is found that even the short (20 min) ion-plasma treatment results in the formation of nitrided layers with the thickness of up to 40 μm and microhardness of up to 9 GPa.The high speed of nitriding can be explained as a result of the joint action of high ion flux density and high ion energy on the sample surface