Tribološke lastnosti jekla nitriranega v plazmi in prekritega z DLC-prevleko

B. Podgornik, J. Vižintin, V. Leskovšek, H. Ronkainen, K. Holmberg

Materiali in tehnologije 34 (2000) 375–379.

Abstract

Raziskali smo tribološke lastnosti jekla 42CrMo4, nitriranega v plazmi in prekritega z zaščitno prevleko na osnovi trdega ogljika (DLC). Pred tribološkimi preizkusi smo z metalografijo, elektronsko in optično mikroskopijo, merjenjem mikrotrdote in zaostalih napetosti ter oprijemljivosti prevleke, ovrednotili kontaktno tehnično površino. Tribološke preizkuse smo opravili pri izmeničnem in enosmernem drsenju brez maziva. Za določitev vpliva nitriranja ter prisotnosti spojinske plasti na tribološke lastnosti kompozita prevleka-podlaga smo trdo zaščitno prevleko nanesli na kaljeno jeklo in na jeklo, nitrirano v plazmi. Nitriranje v plazmi pa je bilo izvedeno pri dveh različnih razmerah, v atmosferi z zelo nizko vsebnostjo dušika ter v klasični 25% dušikovi atmosferi. Rezultati raziskave so pokazali, da v primerjavi s kaljenjem, nitriranje jekla močno izboljša obrabno odpornost kompozita prevleka-podlaga, kar je bilo ugotovljeno tako za enosmerno, kakor tudi za izmenično drsenje. Sam nanos prevleke na osnovi trdega ogljika pa vodi do zelo ugodnih tornih lastnosti (μm = 0,1). Četudi so predhodne raziskave nakazale negativen vpliv spojinske plasti je bilo ugotovljeno, da spojinska plast, ki nastane pri natančno nadzorovanem procesu nitriranja v plazmi, lahko vodi do močno izboljšane obrabne odpornosti kompozita prevleka DLC-podlaga.

Samples made of AISI 4140 steel were surface treated by plasma nitriding and coated with a hydrogen-free hard-carbon coating. The specimens were investigated in terms of their microhardness, residual stress, coating adhesion and dry-sliding wear resistance. Wear tests in which duplex-treated specimens were mated to hardened ball-bearing steel were performed under unidirectional and reciprocating sliding. To examine the influence of the nitriding conditions on the performance of duplex-treated steel, the coating was deposited on hardened as well as on plasma-nitrides samples, nitrided under two different nitriding conditions. The results show a greatly improved sliding wear resistance of the plasma-nitrided hard-coated specimens compared with un-coated and pre-hardened specimens, for both unidirectional and reciprocating sliding. Furthermore, a hydrogen-free hard-carbon coating produced a reduction in the coefficient of friction of about one order of magnitude. Although previous investigations showed a negative effect of the compound layer, it was found that this layer may act as an intermediate hard layer, leading to superior tribological properties of the composite.

Keywords: nitriranje v plazmi, prevleka trdega ogljika, drsenje, obraba, plasma nitriding, DLC coating, dry sliding, wear

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