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The aim of this paper was to investigate the potential of using hard physical vapour deposition (PVD) coatings on forming tools. A tribological evaluation of TiN, TiB2, TaC and diamond like coating (DLC) coatings deposited on cold-worked tool steel was carried out in a load-scanning test rig and compared to the behaviour of different uncoated forming tool steels. The special test configuration, where austenitic stainless steel was used as the counter-material, makes it possible to gradually increase the normal load during forward sliding strokes, and to correspondingly decrease the load during reversed ones. In this investigation, the load range was 100 to 1300 N (contact pressure from 1 to 5 GPa). The experimental results indicate that theintroduction of an appropriate hard coating will lead to an improved wear resistance and a longer lifetime for the forming tool. Furthermore, by using hard low-friction coatings excellent anti-sticking properties can be obtained. Namen predstavljenega prispevka je bil raziskati moznosti uporabe trdih prevlek fizikalno nanesenih v vakuumu (FNV - PVD) na orodjih za hladno preoblikovanje. V raziskavo so bile vključene prevleke TiN, TiB2, TaC in diamantu podobna prevleka na podlagi trdega ogljika (DPP), katerih tribološke lastnosti smo primerjali z različnimi orodnimi jekli za delo v hladnem jeklarne Uddeholm Tooling iz Švedske. Tribološke lastnosti materialov, vključenih v raziskavo, smo določili na preizkuševalisču, katerega izoblikovanost omogoča izmenično in zvezno povečevanje ter zmanjsevanje obremenitve med drsenjem. Obremenitev je bila v območju med 100 in 1300 N (kontaktni tlak med 1 GPa in 5 GPa), kot protimaterial pa smo uporabili avstenitno jeklo. Rezultati raziskave kazejo, da uporaba ustrezne prevleke privede do povečane obrabne obstojnosti orodja ter do precejšnjega zmanjšanja pojava lepljenja obdelovanega materiala na površino orodja.

In our study samples made of 42CrMo4 steel pre-treated by plasma nitriding and coated by two different PVD coatings (TiN and TiAlN) were investigated with respect to the microhardness, surface roughness, stretch adhesion and the dry sliding wear resistance. Wear tests in which duplex treated pins were mated to hardened ball bearing steel discs were performed on pin-on-disc machine. To examine the influence of nitrided zone on the performance of coating-substrate composite coatings were deposited on hardened as well as on plasma nitrided samples nitrided under two different nitriding conditions; inconventional 25%?$N_2$? and in ?$N_2$? poor gas mixture. Results show that compared to hardening plasma nitriding improves sliding wear resistance of hard coated 42CrMo4 steel. Although previous investigations showed a negative effect of the compound layer, it was found that a precisely controlled plasma nitriding process can lead to dense, uniform and well-adherent compound layer with a positive effect on the wear properties of pre-nitrided and hard-coated AISI 4140 steel. V okviru našega dela smo raziskali tribološke lastnosti jekla 42CrMo4, nitriranega v plazmi in prekritega z dvema različnima zaščitnima prevlekama (TiN in TiAlN). Pred tribološkimi preizkusi smo z metalografijo, elektronsko in optično mikroskopijo, z merjenjem mikrotrdote in topografije površine ter oprijemljivosti prevlek ovrednotili kontaktno tehnično površino. Tribološke preizkuse smo opravili na napravi valjček-disk pri suhem drsenju. Za ugotovitev vpliva nitriranja, njegove globine in spojinske plasti na tribološke lastnosti kompozita prevleka-podlaga smo trdi zaščitni prevleki nanesli na kaljeno jeklo, kakor tudi na jeklo, nitrirano v plazmi. Samo nitriranje v plazmi pa je bilo izvedeno pri dveh različnih okoliščinah, v atmosferi z zelo nizko vsebnostjo dušika ter v klasični atmosferi s 25% ?$N_2$?. Rezultati kažejo, da v primerjavi s kaljenjem plazemsko nitriranje jekla 42CrMo4 izboljša protiobrabno odpornost nanesenih trdih zaščitnih prevlek. Čeprav so predhodne raziskave pokazale negativen vpliv spojinske plasti, pa natančno vodeno plazemsko nitriranje omogoča nastanek homogene spojinske plasti s pozitivnim učinkom na protiobrabne lastnosti plazemsko nitriranega jekla 42CrMo4, prekritega s trdo zaščitno prevleko.