Directional Recrystallization Processing

Abstract

Abstract : Fundamental research has been undertaken to understand how key microstructural parameters (grain size, particle spacing) interact with the processing conditions (temperature, rate of hot zone movement, temperature gradient in front of the hot zone) to control the microstructural evolution during directional recrystallization processing. The work involved close coupling of experiments with computer simulations. The computer simulation, in part, was to guide the choice of experimental parameters. A front-tracking grain-growth model was used to investigate the effects of hot zone width on the development of a columnar-grained structure and on its continued propagation. Analytical models were developed to explain both the critical hot zone velocity for the continued propagation of a columnar-grained structure and the relationship between the critical hot zone velocity and the hot zone width. The role of grain boundary energy and mobility on the development of a columnar grain structure were also explored. Experiments showed that most columnar grains produced in cold-rolled, directionally-recrystallized nickel have a ?124! orientation. Small island grains left inside the columnar grains were shown either to have low-angle boundaries or to be twins.