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Cast iron and the self-lubricating behaviour of graphite under abrasive wear conditions
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.ORCID iD: 0000-0003-2698-5445
Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting. Scania CV AB, Materials Technology, SE-151 87 Södertälje, Sweden.
2014 (English)Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Cast iron is assessed as a self-lubricating material under sliding conditions. This is due to the graphite particles distributed in the matrix, which come out from their pocket, and form a tribofilm between the mating surfaces, and by which improve the tribological characteristics. In this study, the directionality and the interaction between the graphite and matrix material was investigated by microindentation and microscratch techniques. The results showed that the graphite is fractured and pushed out from the middle of graphite lamellas as a result of indentation. It was also observed that the graphite orientation below the surface intensely influenced the pushing out behaviour. For the graphite oriented toward the indenter position, the effect was more pronounced. Moreover, it was found that a scratch test can be used to investigate and explain the graphite pushing out tendency. The result was used to explain the directionality and closing tendency of the graphite lamellas during sliding.

Place, publisher, year, edition, pages
2014.
Keywords [en]
lamellar graphite iron, graphite self-lubricating behaviour, tribological performance, microindentation test, microscratch test
National Category
Other Mechanical Engineering
Identifiers
URN: urn:nbn:se:hj:diva-25199OAI: oai:DiVA.org:hj-25199DiVA, id: diva2:767209
Conference
10th International Symposium on the Science and Processing of Cast Iron – SPCI10
Funder
EU, European Research Council, 265861 (Helios)Available from: 2014-12-01 Created: 2014-12-01 Last updated: 2025-02-14Bibliographically approved
In thesis
1. The influence of microstructure on mechanical and tribological properties of lamellar and compacted irons in engine applications
Open this publication in new window or tab >>The influence of microstructure on mechanical and tribological properties of lamellar and compacted irons in engine applications
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lamellar graphite iron (LGI) is commonly used in diesel engine applications such as piston rings–cylinder liner where an excellent combination of physical and tribological properties is essential to avoid scuffing and bore polishing issues. The excellent tribological behaviour of LGI alloys is related to the graphite lamellas, which act as solid lubricant agents by feeding onto the tribosurfaces under sliding conditions. However, increasingly tighter emissions and fuel economy legislations and the higher demands on enhanced power and durability have encouraged both engine designers and manufacturers to introduce pearlitic compacted graphite irons (CGI) as an alternative material replacing LGI, although the poor machinability of pearlitic CGI alloys compared to the LGI remains a challenge.

The focus of this study is placed on investigating how the microstructure of LGI and CGI alloys affects their mechanical and tribological properties. This was initially undertaken by investigating representative, worn lamellar cast iron piston rings taken from a two-stroke large-bore heavy-duty diesel engine. As known that it is tribologically essential to keep the graphite open under sliding conditions, in particular under starved lubrication regimes or unlubricated conditions to avoid scuffing issues; however, this study revealed the closure of a majority of graphite lamellas; profoundly for those lamellas that were parallel to sliding direction; due to the severe matrix deformation caused by abrasion. Both microindentation and microscratch testing, which were used to crudely simulate the abrasion under starved lubricated condition in combustion chamber, suggested a novel mechanism of activating the graphite lamellas to serve as lubricating agents in which the matrix deformation adjacent to the graphite initially resulted in fracturing and then extrusion of the graphite lamellas.

Additionally, in order to investigate the relation between matrix constituents, mechanical properties and machinability of cast iron materials, solution-strengthened CGI alloys were produced with different levels of silicon and section thicknesses. The results showed significant improvements in mechanical properties and machinability while deteriorating the ductility. Moreover, multiple regression analysis, based on chemical composition and microstructural characteristics was used to model the local mechanical properties of high Si ferritic CGI alloys, followed by implementing the derived models into a casting process simulation which enables the local mechanical properties of castings with complex geometries. Very good agreement was observed between the measured and predicted microstructure and mechanical properties.

Place, publisher, year, edition, pages
Jönköping: Jönköping University, School of Engineering, 2016. p. 80
Series
JTH Dissertation Series ; 17
Keywords
Cast iron, Si solution-strengthened CGI, microstructure, mechanical properties, modelling and simulation, tribology, abrasive wear, scratch testing
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-32052 (URN)978-91-87289-18-7 (ISBN)
Public defence
2016-11-25, E1405, Jönköping University, School of Engineering, Jönköping, 10:00 (English)
Opponent
Supervisors
Available from: 2016-10-26 Created: 2016-10-26 Last updated: 2016-10-26Bibliographically approved

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Ghasemi, RohollahElmquist, Lennart

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