Effect of Grain Boundaries and Grain Orientation on Structure and Properties
- PDF / 1,010,697 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 112 Downloads / 230 Views
ODUCTION
THE microstructure evolution during plastic deformation of polycrystals may differ from that of single crystals due to grain interaction. A first attempt to relate the behavior of single crystals and polycrystals was made by Sachs,[1] who suggested that individual grains in polycrystals deform like free single crystals. However, as strain continuity must be maintained across the grain boundaries, it was suggested by Taylor[2] that all the grains in a polycrystal undergo the same homogeneous strain as the bulk material. Such a homogeneous strain will, in general, require slip on at least five slip systems.[3] The presence of grain boundaries was not taken into account in the Taylor model. Boundaries may, however, be effective barriers to slip so that local stresses potentially build up in the grain boundary region. These may be relaxed by secondary slip. As a result, the microstructure evolving in the grain boundary region may differ from that of the grain interior. The structural evolution in these regions will be presented in the following as an overview based on structural subdivision by deformation-induced dislocation boundaries. In the next section, correlations will be presented on the grain scale between the characteristics of the deformation microstructure and the crystallographic orientation of the grain in which it forms. This leads to a comparison of polycrystal and single-crystal behavior followed by a general analysis of active slip systems. In a final section, N. HANSEN, X. HUANG, and G. WINTHER, Senior Scientists, are with the Danish-Chinese Center for Nanometals, Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark, DK-4000 Roskilde, Denmark. Contact e-mail: [email protected] Manuscript submitted December 23, 2009. Article published online July 13, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
the mechanical behavior of single crystals and polycrystals will be discussed.
II. DEFORMATION MICROSTRUCTURE—GENERAL The characterization and analysis of deformation microstructures will in the present paper be limited to fcc metals with medium to high stacking fault energy ranging from 45 mJ/m2 (Cu) to 166 mJ/m2 (Al).[4] Only cold deformation will be discussed and at strain rates where diffusional processes are considered to be negligible. As to deformation, monotonic deformation processes like tension and rolling will be included. By these processes, the equivalent strain (evM) has been varied from low to medium levels (about 0.05 to 0.5, where single glide is precluded). As a general guideline for the structure analysis, it is assumed that the dislocations are stored in low-energy configurations almost free of longrange stresses.[5–7] A. Grain Boundary Region The effect of grain boundaries during plastic deformation was introduced by Kockendo¨rfer[8] who suggested that the interior of a grain in a polycrystal may deform like an isolated single crystal and the misfit where the grains meet might be accommodated elastically or plastically. Strain accom
Data Loading...
