X-RAY-DIFFRACTION CHARACTERIZATION OF FLAKE AND COMPACTED GRAPHITE INCAST-IRON

An X-ray diffraction study was carried out on bulk samples of directio nally solidified gray cast iron, some of which contained oriented flak e and others oriented compacted (vermicular) graphite. It was observed that flake graphite exhibited crystallographic preferred growth direc tion relationships with respect to austenite, primarily [11.0]G, [10.0 ](G) parallel-to [100](gamma) parallel-to GD, and to a lesser extent, {10.1}G perpendicular-to GD. This suggests that there is also a prefer ential plane coupling at graphite-austenite interface. Besides, no lat tice distortions were found in flake graphite. Bulk sample results giv e reliable evidence of the existence of rotation twins, supporting the most commonly accepted mechanism for flake growth based on rotation b oundary steps. By contrast, oriented compacted graphite, which was gro wn by means of a specially designed technique of addition in situ, sho wed random crystallographic orientation and great lattice distortions. There was no evidence of a change in a preferential growth mode from [a over arrow pointing right] to (c over arrow pointing right) directi on.