Local ion nitriding of martensitic structural steel in plasma of glow discharge with hollow cathode
A probe research of glow discharge plasma was carried out by a single cylindrical Langmuir’s probe technique at a pressure of 60 Pa in a gas mixture of 70% Ar + 30% N2. Distributions of charged particle densities in a cavity formed by a technological screen to create a hollow cathode efect and treated material surface are obtained. It was established that the hollow cathode efect leads to increasing of ion concentration near the cathode surface during ion nitriding in a glow discharge. The maximum ion concentration in the center of a cathode cavity is ni =3.5·10 16m-3. Efects of the local ion nitriding in the plasma of glow discharge with a hollow cathode as well as the duration of plasma treatment process on the microhardness and structure of difusion layer of martensitic structural steel at the temperature of 550°C have been studied. Difusion saturation process for martensitic steel local ion nitriding is found to be described by the inverse parabolic law. It is proved that smoothing of microhardness distribution through hardened case is rising with rise of duration of nitriding in plasma of glow discharge with hollow cathode. Three zones are formed in steel surface as a result of the local ion nitriding: plasma modiied zone, transition zone, and not modiied zone. The thickness of difusion layer in the zone modiied with plasma of glow discharge with hollow cathode efect is two times greater than that in the zone modiied without hollow cathode efect.