1991 Volume 55 Issue 7 Pages 739-747
To clarify the mechanism of normal grain growth and the preferred order of migration among grain boundaries, computer simulation of two-dimensional normal grain growth was carried out for the grain structures generated by the constant nucleation rate and growth model.
Five kinds of processes which are different in the preferred order of grain boundary migration were investigated, and grain structures after each simulation time were compared in terms of the grain size distribution, distribution of number of sides per grain, average morphological characteristic values, average grain diameter, etc. The five kinds of processes are: (1) large grains grow against the neighboring smaller ones in order of largeness, (2) small grains shrink against the neighboring larger ones in order of smallness, (3) grains, if smaller than the neighboring ones, shrink, and if larger, then they grow, and both happen simultaneously in random order. (4) grains grow only against the neighboring smaller ones in random order, and (5) grains shrink only against the neighboring larger ones in random order. The results are summarized as follows:
(1) Within the present simulation times, the average morphological characteristic values were almost the same in all of these five processes.
(2) The average grain area increased slightly in the first few simulations, then remarkably, and as more simulations were made, they increased slowly again.
(3) The logarithm of the average grain diameter decreased slightly at first for the logarithm of simulation time, but then it increased at a constant rate. The reciprocal grain growth exponent was 0.42 for the arithmetic mean diameter and 0.53 for the geometric mean diameter.
(4) In every simulation, the distributions of grain diameters were approximately log-normal in shape, while the distributions of numbers of sides per grain were normal in shape.
(5) The distributions of relative grain diameters and number of sides per grain was time-invariant.
(6) In the processes (3) and (4), the frequency of number of sides per grain was maximum at 5 sides in the first several simulation times, but later it became maximum at 6 as the theory predicts.
