Volume Expansion of Compacted Graphite Iron Induced by Pearlite Decomposition and the Effect of Oxidation at Elevated Temperature
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Engine cylinder blocks and heads, made of compacted graphite iron, are subjected to prolonged periods of cyclic heating and cooling. These conditions may give rise to the decomposition of the pearlite matrix accompanied by the formation of lower-density graphite and oxides, which will lead to an increase of material volume. The microstructural instability deteriorates the physical and mechanical properties of CGI and accordingly the thermal fatigue properties. In the present work it was shown that the extent and mechanism of volume change are drastically affected by the presence of an oxide atmosphere. It was found that after annealing under atmospheric conditions internal oxidation largely inhibited the progress of pearlite decomposition and therefore much smaller growth rates were obtained as compared to those observed under vacuum conditions in the dilatometer. After 16 h of annealing time at 700 °C in vacuum, the CGI samples exhibited 6 times faster growth kinetics as compared to annealing in open atmosphere.
KeywordsCompacted graphite iron (CGI) Volume expansion Oxidation Pearlite decomposition Dilatometer
This research was carried out under project number MC2.06270 in the framework of the Research Program of the Materials innovation institute M2i (www.m2i.nl). Authors would like to thank DAF Trucks N.V. Central Laboratories for their contributions and provision of material for this research.
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