An ultrafine-grained surface layer was fabricated on a pure Fe plate by the shot peening process. The average grain size within the surface layer of 10μm thick was about 28nm. The diffusion kinetics of Al was measured by secondary ion mass spectrometry at 300 to 380C. The diffusion coefficient of Al in the nanocrystalline layer was about 4 orders of magnitude higher than that in coarse-grained Fe. The activation energy of Al diffusion in nanocrystalline layer was 1.38eV, which was much smaller than that reported for Al diffusion in the conventional Fe. The enhanced diffusivity of Al may originate from a considerable amount of non-equilibrium grain boundaries and a high density of dislocations in the surface layer processed by shot peening.

Diffusion Behavior of Aluminum in the Surface Layer of Iron Processed by Shot Peening. C.Zhong, L.Liu, Y.Wu, Y.Deng, B.Shen, B.Shu, W.Hu: Materials Letters, 2010, 64[12], 1407-9