High-temperature phase transformations of iron anhydrous ammonia system realized by ball milling at room temperature

alpha-Fe powder has been ball milled at room temperature in an anhydrous ammonia atmosphere for various times. The composition and structure of milled powders was investigated using x-ray diffraction spectroscopy, Mossbauer spectroscopy, combustion elemental analysis, and thermal analysis. A high temperature reaction sequence was observed during milling in the nitrogen composition range from 3.75 to 5.56 wt %. The nitriding reaction sequence has been established as a function of milling time. An increase of nitrogen in the powder with an increase of milling time produces a progression to iron nitride phases richer in nitrogen. A distinct similarity is found between nitriding reaction processes during high-energy ball milling and nitrogen ion implantation into iron. Additionally, an inverse (dissociation) reaction sequence is observed during thermal treatments of ball-milled iron powders. (C) 1996 American Institute of Physics.