The performance and mechanisms of DLC-coated surfaces in contact with steel in boundary-lubrication conditions : a review

I. Velkavrh, M. Kalin, J. Vižintin

Strojniški vestnik 54 (2008) 189–206.

Abstract

Pomembnost trdih prevlek v različnih strojnih uporabah skokovito narasča že več kot 20 let. Razvoj novih materialov kot npr. sodobne keramike, diamantu podobnega ogljika ter nano-kompozitnih prevlek je vzpodbudil intenzivne znanstvene raziskave na področju tribologije in inženiringa površin, ter hkrati usmeril pozornosti v področje mikro/nano tehnologij. Prevleke iz diamantu podobnega ogljika - DLC - so trenutno ena izmed najbolj perspektivnih vrst trdih prevlek. Njihove glavne prednosti so majhno trenje, dobre proti-obrabne lastnosti, adhezijska zaščita, in druge. Vendar pa je zaradi nizke povrsinske energije DLC prevlek njihova reaktivnost s konvencionalnimi olji in aditivi slabša. Za kakovosten preskok, ki bi izboljšal delovanje in omogočil učinkovito optimizacijo ter izboljšano "konstrukcijo" mejno mazanih DLC stikov za različne mehanske sisteme, je potrebno razumeti zakaj, kako, pod katerimi pogoji in s katerimi vrstami DLC prevlek ter mazivi je njihovo mejno mazanje sploh mogoče. V desetletju raziskav tega področja je bilo objavljenih ze precej rezultatov, vendar so le-ti zaradi različnih tipov prevlek, maziv in aditivov v posameznih studijah pogosto neprimerljivi in včasih tudi nasprotujoči. Veliko povečanje zanimanja za uporabo DLC prevlek v mazanih sistemih v različnih vejah industrije pa zahteva poglobljeno razumevanje mehanizmov mazanja in celostnega delovanja teh prevlek. Ravno zato je, za skokovit napredek na tem področju, potreben pregled trenutnega stanja in sinteza precej razpršenih rezultatov dosedanjih raziskav mazanih DLC-stikov. V predstavljenem prispevku je podana analiza triboloških lastnosti stikov DLC/jeklo in predpostavljenih mehanizmov mazanja iz do sedaj objavljenih študij. Povzeli smo temeljne ugotovitve in trenutno razumevanje mejnega mazanja kontaktov DLC/jeklo, s čimer dopolnjujemo našo podobno analizo opravljeno za stike DLC/DLC. The importance of hard coatings in mechanical applications has been increasing rapidly for more than 20 years. The development of novel coatings, such as improved ceramic, diamond-like-carbon and advanced nano-composites, has promoted scientific research in the field of tribology and surface engineering, and at the same time it has focussed attention on micro- and nano-technologies. Diamond-like-carbon (DLC) coatings are becoming one of the most promising types of hard coatings. Their main advantages are low friction,good anti-wear properties, and adhesive protection. However, due to their low surface energy their reactivity with conventional oils and additivesis limited and remains unsatisfactory. For a qualitative step-change that would improve the performance and allow effective optimising and tailoring of boundary-lubricated DLC contacts for various mechanical systems it is necessary to understand the mechanisms of why, how, under which conditions, and with which types of DLC coatings and lubricants the actual boundary lubrication is possible. As a result of ten years of research in this field, a lot of data have been reported: however, due to the different types of coatings, lubricants and additives used in these studies, the results are often difficult to compare and are sometimes contradictory. As a result of the recent heavy demand from many industries to apply DLC coatings to lubricated systems, a much better understanding of these phenomena and their overall performance is required. Therefore, if we wish to see a more effective continuation of the research and a better understanding of the scattered results, an overview of the current state of the art of lubricated DLC contacts is needed. In this paper we analyse the performance and suggested boundary-lubrication mechanisms of DLC/steel contacts from already-published studies and we summarise our present understanding of the boundary lubrication in DLC/steel contacts, which complements our recent analyses of DLC/DLC contacts.

Keywords: DLC prevleke, aditivi, nanotribology, mejno mazanje, olja, boundary lubrication, nanotribologija, diamond-like carbon coatings, additives, base oil

URL: http://www.sv-jme.eu/arhiv/sv-jme-letnik-2008/strojniski-vestnik-54-2008-3/

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