Grain growth kinetics of nanocrystalline nickel produced by surface mechanical attrition treatment

By means of surface mechanical attrition treatment(SMAT) technique,a nanocrystalline surface layer is produced in Ni plate.The grain growth kinetics of nanocrystalline Ni is studied by XRD and TEM.The grain growth kinetics parameters,time exponent n and activation energy Q,are determined respectively.The value of n is about 0.14 in the temperature range from 423 K to 723 K.When annealed from 423 K to 523 K,the activation energy Q value for nanocrystalline Ni is 32.1 kJ/mol,suggesting that grain growth is governed by the re-ordering of grain and subgrain boundaries.When annealed from 523 K to 723 K,the Q value is 121.3 kJ/mol,suggesting that grain growth is governed by the grain boundary diffusion.Abnormal grain growth is observed by TEM during annealing at high temperatures.