The distribution of grain boundary and interface plane orientations in transformed microstructures

The properties of interfaces depend not only on the lattice misorientation, but also on the interface plane orientation. Extensive studies of grain boundaries led to the conclusion that in systems evolving by grain growth, the relative areas of different grain boundary planes are inversely correlated to their relative energies. In other words, the low energy grain boundary planes make up a larger part of the population than the higher energy grain boundary planes. The hypothesis of this work is that the interface plane orientation distribution in transformed microstructures depends more on the mechanism of formation than on the relative energy. After a discussion of methods for measuring interface plane orientations, results will be presented for lath martensite in a low carbon steel and for martensite in a Ti-6Al-4V alloy processed in two different ways to promote a displacive transformation in one case and a diffusional transformation in the other.