The β→αTransformation in Poly crystalline SiC: III, The Thickening of α Plates

The final stages of the β→α polymorphic phase transformation in conventionally sintered and hot‐pressed SiC were studied by optical and transmission electron microscopy. The interface between the α and β regions of partially transformed grains invariably contains thin α lamellae adjacent and parallel to coherent β twins (or β stacking faults). These planar defects serve as nucleation sites for the transformation, with growth of α occurring by the motion of partial dislocations nucleated at the intersection of coherent and incoherent twin boundaries. Various structural phenomena in SiC, including faulting, mi‐crosyntaxy, and long‐period polytypism, are discussed in terms of this transformation mechanism.