In-situ studies of phase transformations in iron alloys

The topic of this thesis covers a broad range of phenomena through three significant phase transformations in iron alloys, being solidification, delta-ferrite to austenite and austenite decomposition. An appreciation of the links between these diverse transformations is necessary to understand the purpose of the present study. One such link is the concept of morphological stability of interphase boundaries during transformations. Another link between the three phase transformation is the lack of studies conducted utilising in-situ, real-time observations of phenomena. With the advent of high temperature laser scanning confocal microscopy, it is now possible to overcome previous experimental difficulties associated with resolving images at high temperature. Therefore, experimental analysis can be conducted into not just the morphology of transformation interfaces, but into a range of additional phenomena such as the development of recovery structures and growth kinetics. For the studies conducted utilising LSCM it was necessary, due to the novelty of the technique, to establish both a frame of reference for interpreting observations, and to characterise the influence of the free surface on the observations. In regard to the nexus between events on the free surface and in the bulk, endeavours were undertaken to establish phenomena that are affected by the free surface and those that are not. Serial sectioning analysis has led to the conclusion that solid-state phase transformations of delta-ferrite to austenite and austenite decomposition do show a correlation between events on the free surface and those in the bulk. Phenomena that do not exhibit a nexus between events on the free surface and in the bulk were identified. These were the pinning of grain boundaries by surface defects, anomalous massive phase transformations and precipitation of non-metallic particles. The aim of the experimental studies into the relationship between crystallographic orientation and the