DIFFUSIONAL-DISPLACIVE PHASE TRANSFORMATIONS AND RELATED ISSUES

摘要

Comparisons among martensitic, ledgewise diffusional and diffusional-displacive (D-D) transformation mechanisms show that the D-D one is confusing and self-contradictory. Whereas the displacive mechanism is equivalent to that of martensite, the reconstructive mechanism seems primarily useful in identifying crystal symmetries that cannot undergo a displacive transformation. The absence of closely spaced twins or of a glissile interfacial structure can at least partially explain the inability of the phenomenological theory of martensite crystallography to account for plates formed by a ledgewise diffusional mechanism. Whereas the martensitic (and D-D) mechanisms can explain only invariant plane strain (IPS) surface reliefs, secure identification has now been made of IPS, tent and inverse tent reliefs associated with monocrystalline plates or laths associated with ledgewise diffusional transformations. All such reliefs can be explained by ledge-based mechanisms.