Microtexture evolution during annealing and superplastic deformation of Al-5 pct Ca-5 pct Zn
- PDF / 453,715 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 69 Downloads / 247 Views
I.
INTRODUCTION
THERMOMECHANICAL processing (TMP) is necessary in order to develop the microstructural characteristics that are required to enable superplastic response in aluminum alloys. These characteristics also evolve during subsequent annealing and straining of the material. Recovery during the initial stages of such annealing involves annihilation and rearrangement of dislocations and an associated sharpening of the deformation texture produced by the TMP; usually, no new texture components appear. At least two alternative subsequent transformation processes have been recognized. Most commonly, recrystallization takes place via the formation and migration of high-angle grain boundaries beginning in regions of high lattice curvature and driven by the reduction in stored energy achieved by elimination of the deformation microstructure. In general, this results in the replacement of deformation texture components with recrystallization texture components, although a complete theory of recrystallization texture formation remains to be developed.[1] However, it has also been observed that, in some particlecontaining alloys, in which grain boundary migration is inhibited, the differences between recovery and recrystallization are not as distinct. Instead, prolonged annealing results in the development of a fully recrystallized microstructure in the absence of long-range migration of highangle boundaries, and components of the deformation texture are seen to persist throughout the annealing process. M.T. PE´REZ-PRADO, Graduate Student, O.A. RUANO, Professor of ´ LEZ-DONCEL, Research Scientist, are with the Research, and G. GONZA Department of Physical Metallurgy, Centro Nacional de Investigaciones Metalu´rgicas (CENIM), CSIC, 28040 Madrid, Spain. T.R. McNELLEY, Professor, is with the Department of Mechanical Engineering, Naval Postgraduate School, Monterey, CA 93943-5000. Manuscript submitted April 21, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS A
This phenomenon has been referred to as ‘‘extended recovery,’’ ‘‘recrystallization in situ,’’ or, most commonly, as ‘‘continuous recrystallization.’’ It was first studied by Hornbogen and co-workers[2,3] and subsequently has been observed in several materials including some superplastic aluminum alloys.[4–9] A detailed description of the mechanisms involved, however, still remains to be developed. Since the classic work of Pearson,[10] grain boundary sliding (GBS) has been considered as the main deformation mechanism responsible for superplasticity.[11–13] However, GBS requires an accommodation mechanism in order to occur and the details of the accommodation process have remained unclear. Several studies have suggested that slip may contribute to accommodation as well as to the total strain during superplastic straining.[5,14] All of the microscopic changes that take place in the microstructure of materials during deformation have a cumulative effect on the texture of a processed and deformed material; thus, texture analysis constitutes a powerful tool to investigate
Data Loading...
