Wear and friction behaviour of duplex-treated AISI 4140 steel

B. Podgornik, J. Vižintin, O. Wänstrand, M. Larsson, S. Hogmark

Surface & Coatings Technology 120/121 (1999) 502–508.

Abstract

Nowadays mechanical systems operate in increasingly severe conditions, such as intensive loads, high speeds and harsh environments. Therefore designers are continually stretching the limits of the existing materials. To extend the use of available materials beyond their conventional limits' manufacturers are turning to different surface treatments and to hard protective coatings. The main limitation to more extended use of hard ceramic coatings is the load bearing capacity of the coating-substrate system. Due to very thin nature of the hard ceramic coatings, the substrate must bear the majority of the applied load. If the substrate has insufficient strength to bear the contact loading and thus support the coating, plastic deformation will occur, leading to premature failure of the coating. The challenge to improve the properties of hard ceramic coatings by thermochemical pre-treatment of the substrate has gained much attention in recent years leading to a new method called duplex treatment. Duplex treatment is an interesting method not only for increasing load bearing capacity but also for improving fatigue strength, temperature resistance and wear behaviour of mechanical components, particularly under high loads. In our study samples made of AISI 4140 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, residual stress, scratch 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 and pulse plasma nitrided samples nitrided under two different nitriding conditions; in conventional 25% N₂ and in N₂ poor gas mixture.

Keywords: adhesion, dry sliding, plasma nitriding, TiAlN, TiN

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