On the orientations of abnormally grown grains in nanocrystalline Ni and Ni-Fe.

The scanning electron microscopy-based electron backscatter diffraction technique has been used to determine grain orientations of abnormally grown grains upon annealing in nanocrystalline Ni and Ni-20 at.% Fe electrodeposits. The results show that in nanocrystalline Ni and Ni-Fe, the first grown grains that can be detected are 411 oriented with respect to the normal direction (411//ND). Upon annealing, further grain growth occurs and the dominant orientation of the abnormally growing grains changes from 411//ND to 111//ND. Twinning is found to be the mechanism responsible for the orientation change and is for the first time described in connection with abnormal grain growth in nanocrystalline materials. This means that well-known models for the formation of annealing twins (initially introduced in connection with recrystallization) also seem to apply in nanocrystalline materials.