STRUCTURE AND GROWTH OF PLATELETS IN GRAPHITE SPHERULITES IN CAST-IRON

The structure and orientation of graphite platelets in graphite spheru lites (GS) in cast irons modified by either cerium or magnesium plus c erium were investigated by TEM and micro-diffraction. The platelets ha ve a rhombohedral structure with their [001] directions nearly paralle l to the radius of the GS, but each platelet is twisted about 2-degree s over a 1 mum length. Randomly orientated graphite is located in the interplatelet areas, in which most of the graphite has a hexagonal str ucture rather than rhombohedral structure. Based on the crystallograph ic characterization of the graphite and the cerium and magnesium eleme ntal distribution in the GS, the model for the growth of GS as origina lly proposed by Double and Hellawell is re-examined.