A Mössbauer investigation of zirconium distribution and diffusion in ball milled nanocrystalline iron powders

Abstract

Ball milled nanocrystalline iron with minor zirconium additions was examined using 57Fe Mossbauer spectroscopy and X-ray diffraction. Powder samples were synthesized using 0, 5, and 10 wt.% zirconium additions and milled at room temperature for periods up to 24 h. Progressive decrease in grain size as determined by X-ray diffraction was observed as a function of milling time. Mossbauer spectroscopy indicates increased iron-zirconium coordination with increased milling time. After milling, the powder samples were then heat treated in an inert atmosphere of argon at up to 925 K for various times up to 25 min. Analysis of X-ray peak line width (FWHM) was used to characterize grain size and grain growth kinetics as a function of heat treatment, milling time, and alloy content and reveal an increasingly finer post-heated structure in the alloy samples containing more zirconium. Mossbauer measurements were made and suggest Zr is steadily distributed into the Fe lattice with milling and rapidly diffuses to the grain boundaries with heat treatment. The impurity-rich grain boundaries appear to considerably stabilize the refined structure.