Ball-milled nanocrystalline iron with minor zirconium additions was examined using 57Fe Mössbauer spectroscopy and X-ray diffraction. Powder samples were synthesized using 0, 5 and 10wt% zirconium additions, and milled at room temperature for periods of up to 24h. A progressive decrease in grain size as determined by X-ray diffraction was observed as a function of milling time. Mössbauer spectroscopy indicated an increased iron-zirconium coordination with increased milling time. After milling, the powder samples were heat-treated in an inert argon atmosphere at up to 925K for times of up to 25min. An analysis of X-ray peak line-width was used to characterize grain size and grain growth kinetics as a function of heat treatment, milling time and alloy content. This revealed an increasingly fine post-heated structure in alloy samples containing more zirconium. Mössbauer measurements were performed, and suggested that Zr was steadily distributed into the Fe lattice during milling and rapidly diffused to the grain boundaries with heat treatment. The impurity-rich grain boundaries appeared to stabilize the refined structure considerably.

A Mössbauer Investigation of Zirconium Distribution and Diffusion in Ball Milled Nanocrystalline Iron Powders. M.D.Martin, Y.Fahmy, A.M.Khasanov, J.G.Stevens: Hyperfine Interactions, 2008, 183[1-3], 199-204