Computer simulation of grain growth kinetics with solute drag
- PDF / 436,705 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 80 Downloads / 228 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Computer simulation of grain growth kinetics with solute drag D. Fan P.O. Box 5800, MS 1411, Sandia National Laboratories, Albuquerque, New Mexico 87185
S. P. Chen Theoretical Division, MS B262, Los Alamos National Laboratory, Los Alamos, New Mexico 87545
Long-Qing Chen Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16862 (Received 28 March 1997; accepted 1 June 1998)
The effects of solute drag on grain growth kinetics were studied in two-dimensional (2D) computer simulations by using a diffuse-interface field model. It is shown that, in the low velocity/low driving force regime, the velocity of a grain boundary motion departs from a linear relation with driving force (curvature) with solute drag. The nonlinear relation of migration velocity and driving force comes from the dependence of grain boundary energy and width on the curvature. The growth exponent m of power growth law for a polycrystalline system is affected by the segregation of solutes to grain boundaries. With the solute drag, the growth exponent m can take any value between 2 and 3, depending on the ratio of lattice diffusion to grain boundary mobility. The grain size and topological distributions are unaffected by solute drag, which are the same as those in a pure system.
I. INTRODUCTION
Grain growth is a process of grain boundary migration to decrease total grain boundary area and total free energy of a system, driven by mean curvatures of grain boundaries. The kinetics of grain growth depends strongly on the presence or absence of solute or impurity segregation at grain boundaries. In a pure material, the only process which occurs during grain growth is local atomic rearrangement. If solute segregation is present, the migration of grain boundaries may be controlled by long range diffusion. It is well understood that grain growth follows power growth law Rtm 2 R0m kt with the growth exponent m 2 in a pure material,1–3 where R0 is the initial average grain size, Rt is the average grain size at time t, and k is the kinetic coefficient. Experimentally, however, the growth exponent m is found to be larger than 2 even if a very low impurity level (a few ppm or less) is present in pure metals.1,4,5 Theoretically, Cahn6 studied the effects of solute drag on migration kinetics of grain boundaries by considering the interaction of impurity atmosphere with grain boundaries. Cahn predicted that, according to the migration velocity and driving force, the migration of grain boundaries with impurity segregation can be classified into different regimes: (a) a low velocity/low driving force regime, where long-range diffusion of impurity is important; (b) a high velocity/high driving regime, where long-range diffusion is not necessary and desorption of solute may occur according the diffusivity of impurity; and (c) a transition region between these two regimes. It was also shown J. Mater. Res., Vol. 14, No. 3, Mar 1999
http://journals.cambridge.o
Data Loading...
