Grain-GRowth Kinetics in Nanocrystalline Iron Prepared By Ball Milling

摘要

We have prepared nanocrystalline Fe by ball milling and investigated the kinetics of grai ngrowth at annealing temepratures between 325 deg C and 535 deg C. Three different grain-growth models were used to describe the size-evolution curves: a generalized Hillert growth law with variable exponent (used to describe normal grain growth in the absence of impurities), the Burke equation assuming a constant retarding force on moving grain boundaries, and a third model in which the retarding force scales with the mean grain size owing to impurity enrichment in the grain boundaries. based on the generalized Hillert analysis, a previous invesitgation of grain growth in ball-milled nanocrystalline Fe yielded a temperature-dependent growth exponent that approached the expected value of 0.5 only at high temperatures. In contrast, we find that the grain-growth kinetics in our ball-milled Fe samples are better described by either of the two models accounting for the influence of impurities on the growth rate. Since both models reduce to the ideal Hillert model for negligible ipurity concentrations, their underlying growth exponent is 0.5. This suggests that the temperature dependence of the exponent reported for ball-milled Fe is an artefact of the model used to interpret the grain-growth data.