Wear and friction behaviour of duplex-treated AISI 4140 steel

In this study samples of AISI 4140 steel were pretreated by plasma nitridin g: and coated with two different physical vapour deposited coatings (TIN an d TiAlN). A hardened AISI 4140 sample and a coated sample were also include d in the investigation. To examine the influence of the nitrided zone on th e performance of the coating-substrate composite, two different nitriding c onditions - a conventional 25% N-2 and an N-2-poor gas mixture - were used. The specimens were investigated with respect to their microhardness, surfa ce roughness, scratch adhesion and dry sliding wear resistance. Wear tests in which the duplex-treated pins were mated to hardened ball bearing steel discs were performed in a pin-on-disc machine under dry sliding conditions. Metallography, scanning electron microscopy and profilometry were used to a nalyse the worn surfaces in order to determine the dominant friction and we ar characteristics of the samples investigated. The results show improved w ear properties of the plasma-nitrided hard-coated specimens compared with u ncoated and pre-hardened ones. Although previous investigations showed a ne gative effect of the compound layer, it was found that a precisely controll ed plasma nitriding process can lead to a dense, uniform and highly adheren t compound layer with a positive effect on the wear properties of pre-nitri ded and hard-coated AISI 4140 steel. (C) 1999 Elsevier Science S.A. All rig hts reserved.