PROCESS TECHNOLOGICAL ASPECTS OF THE PRODUCTION AND PROPERTIES OF IN-SITU COMBINED PLASMA-NITRIDED AND PVD HARD-COATED HIGH-ALLOY TOOL STEELS

The successful combination of nitrided high alloy steels with a hard coating requires good compatibility between the structure and properties of the two layers. The technological and economic aspects of the production of such composites are also relevant. A commercial ion plating apparatus was modified to produce a continuous process of pulse plasma nitriding and TiN hard coating on tool steels in the same equipment. The nitriding depth was varied between 15 and 50 mu m in process times with a maximum of 2 h. Special gas mixtures of argon, nitrogen and hydrogen were used to form a diffusion layer with a defined nitrogen content and hardness. The aim of the investigations was to determine the composite properties, such as adhesion, topography and composition (nitride layer, intermediate layer, TiN), hardness, residual stress and tribological behaviour, as a function of the process parameters and the interstage process control in the in situ combined process. With regard to the use of such duplex treated materials, tests for abrasive wear were carried out to characterize the tool behaviour. The properties, in particular the adhesion, can be improved depending on the conditions of pre-nitriding.