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.
Highlights
Compacted graphite iron (CGI) is the material of choice for manufacturing cylinder heads of heavy trucks
Current finite element (FE) simulations of the mechanical behavior of cast iron usually neglect the bonding between the graphite particles and the metal matrix [1,2,3,4,5,6], because there is a lack of knowledge about the magnitude of the interface toughness due to the technical difficulty of measuring this property
(the scatter almost all interfaces are between lamellar pearlite and smooth graphite (LP/NSG), whereas in data of Figure 6 is probably associated with sample preparation and material strength), whereas in the the heat-treated samples, of interfaces be discerned: (i) between ferrite and spiky heat-treated samples, threethree typestypes of interfaces can becan discerned: (i) between ferrite and spiky graphite graphite (F/SG), (ii) between ferrite and non-spiky graphite (F/NSG), and (iii) between lamellar (F/SG), (ii) between ferrite and non-spiky graphite (F/NSG), and (iii) between lamellar pearlite and pearlite andgraphite non-spiky graphiteAdditionally, (LP/NSG)
Summary
Compacted graphite iron (CGI) is the material of choice for manufacturing cylinder heads of heavy trucks Since these cylinder heads are subject to cyclic thermal and mechanical loads in daily startup and shutdown cycles, the CGI component is subjected to thermomechanical fatigue (TMF). There is a growing interest from truck manufacturers in modeling TMF behavior with microstructurally based material descriptors. Current finite element (FE) simulations of the mechanical behavior of cast iron usually neglect the bonding between the graphite particles and the metal matrix [1,2,3,4,5,6], because there is a lack of knowledge about the magnitude of the interface toughness due to the technical difficulty of measuring this property. If one would succeed in measuring the bond strength in a quantitative and reliable manner, the accuracy of such models could be drastically improved.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
