Mechanical alloying process of Fe-Cr powders studied by magnetic measurements

Abstract

A mechanical alloying process for a mixture of elemental Fe and Cr powders with the Cr compositions 20-70 at. % was investigated through the measurements of x-ray diffraction, magnetization, and 57Fe Mijssbauer spectrum. We show that magnetic studies provide more detailed information about the alloying process occurring during ball milling than the conventional diffraction techniques in this particular system. A final product after ball milling was identified as a high-temperature phase of the a solid solution, regardless of compositions studied. Powders subjected to milling in Ar gas atmosphere for 200 h were further ball milled in Nz atmosphere. The presence of N2 gas has caused a partial amorphization. The amorphous phase thus produced is found to be paramagnetic at room temperature.

Mechanically induced phase transformations of the sigma phase of nanograined and of coarse-grained near-equiatomic FeCr alloys

“…As qualitatively similar results were obtained by Fnidiki et al [24,25] for a series of mechanically alloyed Fe-Cr alloys, Shen et al concluded to the existence of a very 'disordered' Fe-Cr + O + N grain boundary structure [26]. By contrast, a nanocrystalline ferromagnetic bcc-Fe 0.50 Cr 0.50 was obtained by Koyano et al [28] by high-energy ball-milling of elemental powder mixtures during 200 h in argon.…”

“…The Mössbauer spectrum of an elemental powder mixture Fe 0.60 Cr 0.40 , milled for 85 h in argon [26], shows, besides the main non-magnetic peak, a weaker and broad magnetic contribution with an average field of ∼12.5 T, much smaller than the field expected for that Cr content. A rather similar Mössbauer spectrum was obtained by Koyano et al [28] with a nanocrystalline Fe 0.50 Cr 0.50 alloy milled for 200 h in argon and further milled under nitrogen. It transformed almost fully into a non-magnetic amorphous phase (Fe 0.50 Cr 0.50 )N 0.058 .…”

“…It transformed almost fully into a non-magnetic amorphous phase (Fe 0.50 Cr 0.50 )N 0.058 . [28]. Unfortunately, Shen et al [26] did not determine the concentrations of O and N in their ballmilled samples.…”

“…The final phases are reported to be either a bcc phase or a bcc phase with a 'disordered' component whose fraction may vary considerably according to the authors. For instance, Koyano et al [28] showed that a sole ferromagnetic bcc phase is formed by ballmilling of equiatomic Fe-Cr elemental powder mixtures during 200 h in argon in a Fritsch P5 planetary ball-mill. By contrast, Shen et al [26] found an almost fully non-magnetic RT Mössbauer spectrum and a bcc X-ray diffraction pattern by ballmilling of Fe 0.60 Cr 0.40 elemental powder mixtures during 85 h in argon.…”

Debye temperature of nanocrystalline Fe–Cr alloys obtained by mechanical alloying

“…For Fe-Cr alloys, several studies conducted by ball milling showed their amorphization e.g. [13][14][15][16][17][18][19][20][21]. In particular, in equiatomic or near-equiatomic FeCr alloys milled in vacuum or argon atmosphere, this effect was observed both in alpha and sigma phases, e.g.…”