EFFECT OF PLASMA NITRIDING ON THE PROPERTIES OF (TI, AL)N COATINGS DEPOSITED ONTO HOT WORK STEEL SUBSTRATES

The properties of polycrystalline (Ti, Al)N coatings deposited on non- nitrided, classically plasma-nitrided and low pressure plasma-nitrided AISI H11 steel samples were investigated. The plasma deposition and l ow pressure plasma nitriding were performed in a Z700-LH magnetron spu tter ion plating unit, while a separate unit was used for plasma nitri ding of specimens at a pressure of several millibars. The (Ti, Al)N co ating was deposited onto all the samples using the same equipment as f or the plasma deposition and low pressure plasma nitriding. For the ch aracterization of the composite structures, the following methods were used: scratch test, X-ray diffraction analysis, scanning electron mic roscopy, scanning tunnelling microscopy and microhardness testing. It was found that plasma nitriding prior to coating deposition strongly a ffects the growth and properties of hard coatings, such as the microha rdness, adhesion, preferred orientation, structure and morphology. Pla sma nitriding at low pressures has a greater effect than does conventi onal plasma nitriding: the adhesion is even more enhanced, the microha rdness is increased, the preferred orientation is more pronounced and the structure is still columnar but more compact.