MOSSBAUER-EFFECT STUDIES OF FE-BASE ALLOYS DURING MECHANICAL ALLOYING AND GRINDING

Mossbauer effect studies of mechanical alloying and mechanical grinding of Fe-B, Fe-Sn and Fe-TM-Al (TM = Ni, Cu), complemented by X-ray diffraction analysis are presented. Some of these systems (Fe-Sn) are especially suited for these type of research because the environments of both elements can be probed. In all cases powders were processed with a Retsch MM 2 horizontal vibratory mill under argon atmosphere. In Fe1-xSnx (0.15 less than or equal to x less than or equal to 0.40), the evolution of mechanical alloying with time and the dependence of the stationary state with composition were investigated. An intermediate superparamagnetic FeSn2 state and a stationary bcc solid solution with composition fluctuations were inferred from the Mossbauer spectra. Solubility of tin into bcc iron was found to be extended up to a maximum of about 22 at.%. Pure powder mixtures of nominal composition Al75Ni10Fe15, Al65Ni20Fe15 and Al63Cu25Fe12 have been mechanically alloyed. Stable disordered crystalline phases were obtained after milling and, in some cases, the partial ordering of bcc structures induced by milling was observed. Further annealings did not produce structural changes but removed the remaining disorder. The characteristic quadrupole interaction parameters were obtained by Mossbauer spectroscopy. The evolution of Fe2B with grinding time was studied. The first milling stage was characterized by fragmentation and accumulation of strain. On further processing, segregation of alpha-Fe occurred while grain size reduction continued and strain was partially removed. For longer grinding times separation of alpha-Fe proceeded at an almost steady rate. Two additional experiments designed to reduce and increase oxygen contamination let us tentatively discard this element as the main responsible for the observed decomposition.