Proposal of characterization procedure of metal-graphite interface strength in compacted graphite iron

Lopez Covaleda, E.A.; Ghodrat, S.; Kestens, L.A.I.; Sacre, Charles Henry; Pardoen, Thomas

doi:10.3390/ma11071159

Proposal of characterization procedure of metal-graphite interface strength in compacted graphite iron

Title

Proposal of characterization procedure of metal-graphite interface strength in compacted graphite iron

Author

Lopez Covaleda, E.A. (Universiteit Gent)
Ghodrat, S. (TU Delft Emerging Materials)
Kestens, L.A.I. (Universiteit Gent)
Sacre, Charles Henry (Katholieke Universiteit Leuven)
Pardoen, Thomas (Katholieke Universiteit Leuven)

Date

2018-07-07

Abstract

Compacted graphite iron is the material of choice for engine cylinder heads of heavy-duty trucks. Compacted graphite iron provides the best possible compromise between optimum mechanical properties, compared to flake graphite iron, and optimum thermal conductivity, compared to spheroidal graphite iron. The vermicular-shaped graphite particles, however, act as stress concentrators, and, as a result of delamination from the metal matrix, they are responsible for crack initiation during the thermomechanical fatigue cycles occurring through engine startup and shutdown cycles. Scratch tests driven over the matrix and into the graphite particles were performed in order to characterize the strength of the metal-graphite interface. Samples extracted from a cylinder head in as-cast condition were compared to samples subjected to a heat-treatment at 700 °C for 60 h. The former samples were composed of a primarily pearlitic matrix and graphite particles (~11.5 vol %), whereas, after annealing, a certain pearlite fraction decomposed into Fe and C, producing a microstructure with graphite-ferrite interfaces, exhibiting a partially spiky morphology. The scratch test revealed that the ferrite-graphite interfaces with spiky nature exhibited a stronger resistance to delamination compared to the ferrite-graphite interfaces with smooth morphology. One reason for the high interface strength is the mechanical interlocking between graphite spikes and ferrite, increasing the contact area between the two phases.

Subject

Bonding strength
Compacted graphite iron
Scratch test

To reference this document use:

http://resolver.tudelft.nl/uuid:4aed1944-3971-48dc-b073-abc61205e49a

DOI

https://doi.org/10.3390/ma11071159

ISSN

1996-1944

Source

Materials, 11 (7)

Part of collection

Institutional Repository