Displacive Phase Transformations in Nanometric Dimension

The present work delves into the role of parent phase size on occurrence of displacive phase transformation with emphasis on transformation in nanometric dimension. Beta phase with compositions suitable for displacive martensitic and omega phase transformations has been generated in different length scales in a Zr-1 wt.% Nb alloy through heat treatment. The beta phase distribution was in the form of (i) patches at grain boundaries and tri-junctions and (ii) needle-shaped intragranular precipitates. The transformation inside the beta phase following quenching has been probed by transmission electron microscopy. Very fine beta precipitates remained untransformed despite their compositions falling in the domain of martensitic, omega phase transformations. The parent phase size dependency was more prevalent in the case of martensitic transformation.