Grain refined surface layers

Activation-limited growth tends to favor compact columnar or equiaxed deposits, while mass transport-limited growth favors formation of loose dendritic deposits. The deposit morphology is modified by using additives. Additives act as grain refiners and levelers because of their effects on electrode kinetics and the structure of the electrical double layer at the cathode surface. Additives that reduce primarily the nucleation overpotential can be considered to be grain-refining additives because of increased secondary nucleation events. 

Broadening the diffraction peaks of ttN — phase formed in modified layer indicates that substructure that was consisted of small individual blocks could be formed additionally inside the grains being refined by friction. Blocks size of bcc-Fe being formed at the very surface layer of the sample treated by FT process was about to 16 nm. Compared to the above block size of aN - phase formed by FN process is found about to 8 nm while it was not more then 10-15 nm at the distance to 0.1 mm from the surface. Indications were obtained that block size increases mostly up to submicro-scaled one when the distance from the surface increases. 

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