MOSSBAUER-EFFECT STUDIES OF FE-BASE ALLOYS DURING MECHANICAL ALLOYINGAND GRINDING

Mossbauer effect studies of mechanical alloying and mechanical grindin g of Fe-B, Fe-Sn and Fe-TM-Al (TM = Ni, Cu), complemented by X-ray dif fraction analysis are presented. Some of these systems (Fe-Sn) are esp ecially 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 e volution of mechanical alloying with time and the dependence of the st ationary state with composition were investigated. An intermediate sup erparamagnetic FeSn2 state and a stationary bcc solid solution with co mposition fluctuations were inferred from the Mossbauer spectra. Solub ility of tin into bcc iron was found to be extended up to a maximum of about 22 at.%. Pure powder mixtures of nominal composition Al75Ni10Fe 15, Al65Ni20Fe15 and Al63Cu25Fe12 have been mechanically alloyed. Stab le disordered crystalline phases were obtained after milling and, in s ome cases, the partial ordering of bcc structures induced by milling w as observed. Further annealings did not produce structural changes but removed the remaining disorder. The characteristic quadrupole interac tion parameters were obtained by Mossbauer spectroscopy. The evolution of Fe2B with grinding time was studied. The first milling stage was c haracterized by fragmentation and accumulation of strain. On further p rocessing, 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 additi onal experiments designed to reduce and increase oxygen contamination let us tentatively discard this element as the main responsible for th e observed decomposition.