Abstract
Nanometer scale and micron scale grain growth of polycrystalline AZ31 Magnesium alloy have been comparatively studied by phase field simulation, and the models are established under realistic spatial-temporal scales. The expression of local free energy density function is modified due to the different initial state of grain growth process at nano scale. The term of grain boundary range is to explain the physical backgrounds of the order parameter gradients at grain boundary and the diffusion grain boundary, and it is related to the correct gradient and coupling parameters. The simulated results are compared in nano scale and micron scale, they are also compared with experimental results in the literature, in order to find out the mechanisms for nano-structural evolution. It is shown that the grain boundary range will cover two adjacent grains in nano scale polycrystalline while the range should be a constant big value of about 1.2μm for grains in micron scale. It is found that the grain growth rate at nano scale is slower than that at the micron scale, and these simulated results can be proved by the experimental results in the literature. It is found that the grain size fluctuation is more intensely in nano-sized grains than that in micron-sized grains by the quantitative analysis of the mixed degree of grains size in nano-structure and micron-structure in the models.
Highlights
IntroductionThe mechanical properties of materials are determined by the microstructure
As we know, the mechanical properties of materials are determined by the microstructure
The grains in micron scale always show the round polygonal shape, which exposes some differences of grain growth mechanisms in nano scale compared with micron scale
Summary
The mechanical properties of materials are determined by the microstructure. The simulated results based on such range model of variation of Ș across a flat boundary are shown in Fig. (b) in nano-structure by our present multiscale phase field model. It is seen from Fig. (a) that, the values of Șj (j represents a certain orientation of the grains) vary in one grain from 1 to 0 into another grain gradually across the grain boundary range. The grain boundary range covers its adjacent two grains in nano scale in Fig. (b), which means that the attribution of the orientation of a grain may be influenced by itself and by its nearest neighbors It is the size and the physical character of the boundary range that makes the key difference in our present model for different scale applications
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