Protiobrabne lastnosti jekla 42CrMo4 nitriranega v plazmi in prekritega s trdo zaščitno prevleko: Wear properties of plasma nitrided and hard coated 42CrMo4 steel

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.