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A study on graphite extrusion phenomenon under the sliding wear response of cast iron using microindentation and microscratch techniques
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.
2014 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 320, no 1-2, 120-126 p.Article in journal (Refereed) Published
Abstract [en]

This study focuses on the graphite flakes extrusion mechanism during microindenting and microscratching of cast iron. Observations on the graphite response under abrasive conditions revealed that the matrix deformation which is occurred during a sliding wear condition could have a significant influence on its lubricating performance. Simple microindentation and microscratch tests were conducted to explore the lamellar graphite contribution to tribofilm formation under abrasive wear conditions. The results obtained showed that induced plastic deformation which developed adjacent to the graphite compressed the lamellas and in turn resulting in extrusion of the graphite from its natural position. Further investigations on both indentation and scratch tests indicated that, surprisingly, the graphite began to be fractured and extruded from the centre of graphite lamellas, irrespective of the lamella size. Additionally, a mechanism was proposed to explain the self-lubricating and the extrusion behaviour of the lamellar graphite as a result of indentation.

Place, publisher, year, edition, pages
Lausanne: Elsevier, 2014. Vol. 320, no 1-2, 120-126 p.
Keyword [en]
Lamellar graphite iron; Graphite extrusion; Sliding wear; Abrasive wear; Microindentation testing; Microscratch testing
National Category
Tribology
Identifiers
URN: urn:nbn:se:hj:diva-24779DOI: 10.1016/j.wear.2014.09.002ISI: 000345156400015Scopus ID: 2-s2.0-84907556394OAI: oai:DiVA.org:hj-24779DiVA: diva2:748681
Projects
Helios
Funder
EU, FP7, Seventh Framework Programme, 265861
Available from: 2014-09-21 Created: 2014-09-21 Last updated: 2017-12-05Bibliographically 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. 80 p.
Series
JTH Dissertation Series, 17
Keyword
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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