A general mechanism of grain growth-Ⅱ: Experimental

The formed microstructure inside polycrystalline materials strongly influences their practical performances, which process is mostly dominated by grain growth behaviors. However, the general evolution of grain growth behaviors, especial for the occurrence of abnormal grain growth and stagnant growth, remains ambiguous despite decades of efforts. Here, we investigate systematically the general evolution of grain growth behaviors by combining a new grain growth theory with grain growth experiments in SrTiO3 polycrystalline materials. The results demonstrate that the observed evolution of grain growth behaviors is in accord with the theoretical predictions, which reveals that the abnormal and stagnant behaviors of grain growth may intrinsically occur in polycrystalline systems due to the existence of non-zero step free energy for grain growth. Furthermore, the general growth theory reveals that normal grain growth results from the roughening transition of grain boundaries which corresponding to step free energy equal to zero. Besides the lower GB energy as commonly believed, the narrower grain size distribution is revealed to play an important role on the thermal stability of grains, which may lead to the counter-intuitive phenomenon of smaller nano-sized grains with higher thermal stability as recently reported in the literature. The general, quantitative growth theory may offer an accurate guidance for the microstructural design with optimal physical properties in polycrystalline materials.