Graphite in metallic materials growths, structures, and defects of spheroidal graphite in ductile iron

Carbon is an important alloying element in the metallic system. Carbon may form graphite particles as a constituent phase in the metallic materials, such as cast irons, nickel alloys, and cobalt alloys. Graphite particles of various morphologies were found in these alloys. Some common morphologies include flake, spherical, and vermicular. Graphite particles of different morphologies offer the alloys unique mechanical and thermal properties. Graphite particles in the metallic systems are generally polycrystalline, which have complex internal substructures separated by crystallographic defects. The graphite particle morphology is a result of crystallographic defects in a particle, depending on the growth mechanism of the particle. A spheroidal graphite particle was bounded with the iron matrix by the basal planes along the surface of the spheroid, with their c-axis approximately parallel to the radial directions. Circumferential growth of basal planes along prismatic directions extends a graphite nodule. Crystallographic defects are essential components to accommodate the curvature in a spheroidal graphite. In this chapter, the crystallographic defects that contribute to graphite morphology accommodation will be introduced, and possible crystallographic defects associated with hexagonal-rhombohedral graphite structure transition will be discussed. These crystallographic defects include but are not limited to c-axis rotation fault, twining/tilt boundary, and stacking fault.