Plasma nitriding enhanced by hollow cathode discharge - a new method for formation of superhard nanocomposite coatings on steel surfaces

The article describes a new method of formation of superhard (greater than or equal to 40 GPa) coatings on surfaces of steel substrates during their nitriding with an auxiliary cathode the surface of which is furnished with holes. The auxiliary cathode fulfills two functions: (i) it intensifies the nitriding discharge by hollow cathode discharges generated in the holes and (ii) strongly sputters the auxiliary cathode material. The sputtered material is transferred onto the surface of nitrided steel samples where it forms a new surface layer. The auxiliary cathode is made of material which contains two elements; Mo and C. This makes it possible to form superhard nanocomposite films. The superhard films are two-phase nanocomposites of the type nc-Mo2C/(a-C + a-Mo2N). Superhard films with hardness of about 53 GPa were prepared. The conditions under which superhard crystalline/amorphous nanocomposites can be prepared are given. (C) 1999 Elsevier Science Ltd. All rights reserved.