PLASMA NITRIDING COMBINED WITH A HOLLOW-CATHODE DISCHARGE SPUTTERING AT HIGH-PRESSURES

The article describes a new plasma nitriding system with an auxiliary cathode the surface of which is furnished with holes of diameter empty set and depth d. The auxiliary cathode fulfills two functions: (i) it intensifies the nitriding discharge by hollow cathode discharges gene rated in the holes and (ii) strongly sputters its material. The sputte red material is transferred onto the surface of nitrided steel sample where it forms a surface layer of nitrides from deposited material. As the material of the auxiliary cathode can be different from that of s amples to be nitrided, the surfaces of nitrided substrates can be impr oved by an addition of selected materials, such as Mo, Cr, Ti, V, etc. The main attention is devoted to the investigation of transfer of the material from the auxiliary cathode onto the surface of nitrided stee l samples. It was found that conditions under which a maximum quantity of this material is transferred depend on dimensions of holes in the auxiliary cathode, potential of treated substrates, and on argon conte nt in N-2 + H-2 + Ar mixture. The plasma nitriding was carried out at a high pressure of 1067 Pa and a substrate temperature T of 550 degree s C for a time of 2.5 h. Detailed measurements of elemental depth prof iles and structure of nitrided steel samples, carried out by means of glow discharge optical emission spectroscopy and x-ray diffraction, re spectively, are given. (C) 1997 American Vacuum Society.