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The relationship between flake graphite orientation, smearing effect, and closing tendency 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.
2014 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 317, no 1–2, 153-162 p.Article in journal (Refereed) Published
Abstract [en]

Abstract Plastic deformation of the matrix during the wear process results in closing the graphite flakes. In this study, the relationship between the deformation of the matrix and the closing tendency of flake graphite was investigated, both qualitatively and quantitatively. Two representative piston rings, which belonged to the same two-stroke marine engine but were operated for different periods of time, were studied. Initial microstructural observations indicated a uniform distribution of graphite flakes on unworn surfaces, whereas worn surfaces demonstrated a tendency towards a preferred orientation. Approximately 40% of the open flakes of the unworn surfaces were closed during sliding, which may result in the deterioration of the self-lubricating capability of cast iron. Moreover, flakes within the orientation range of 0 to 30° relative to the sliding direction showed a maximum closing tendency when subjected to sliding. The closing tendency gradually decreased as the angle increased, approaching a minimum between 30 and 70°. A slight increase in the closing tendency was observed for flakes with orientations between 70 and 90°. A similar trend was observed on both rings. Furthermore, SEM and EDS analysis indicated substantial deformation of the matrix in the area around the flakes. An insignificant corrosion attack was observed on both worn piston ring surfaces.

Place, publisher, year, edition, pages
2014. Vol. 317, no 1–2, 153-162 p.
Keyword [en]
Grey cast iron, Piston ring-cylinder liner, Flake graphite orientation, Sliding wear, Abrasive wear, Graphite closing tendency
National Category
Metallurgy and Metallic Materials Manufacturing, Surface and Joining Technology
Identifiers
URN: urn:nbn:se:hj:diva-24210DOI: 10.1016/j.wear.2014.05.015ISI: 000341340700015Scopus ID: 2-s2.0-84902973160OAI: oai:DiVA.org:hj-24210DiVA: diva2:732863
Projects
European project entitled Helios
Funder
EU, FP7, Seventh Framework Programme, 265861
Available from: 2014-07-07 Created: 2014-07-03 Last updated: 2016-11-29Bibliographically 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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