Structural and magnetic properties of grain boundaries in Fe60Cr40 alloy synthesized by mechanical alloying

Abstract

Mechanical alloying of iron and chromium powder mixtures was performed from 0 to 190 h milling times. X-ray diffraction, Mössbauer spectrometry and differential scanning calorimetry were used to determine the structural and magnetic properties of the intergranular zone, which was associated with a very disordered grain boundary structure, paramagnetic at 300 K. This structure is assumed to be due to the presence of oxygen and nitrogen atoms, forming a mixture of amorphous FeCr + O + N alloy. Between 21 and 85 h, the hyperfine parameters of the magnetic contribution, and therefore the properties of the Fe 60 Cr 40 nanograin cores, are constant, but the paramagnetic fraction associated with the intergranular zone increases. At 85 h, the paramagnetic contribution represents 100% of the Mössbauer spectrum.Moreover, after very long milling times, we have evidenced a de-mixing reaction which results in preferential oxidation and nitrogenation within the very disordered structure.

Mössbauer study on the disordered Fe60Cr40 alloys prepared by mechanical alloying

“…of that is about À0.1 mm/s. It is due to the very disordered Fe-Cr+O+N grain boundary structure as previously reported by Fnidiki et al [11][12][13]. At 85 h, the paramagnetic contribution represents almost 100% of the Mo¨ssbauer spectrum mainly associated with structural changes.…”

“…The Fe-Cr systems exhibit the peculiarities of small heats of mixing and a wide miscibility gap in the phase diagram where both Fe and Cr are insoluble at room temperature. MA of Fe-Cr system has been widely investigated [5][6][7][8][9][10][11][12][13][14] and much attention has been paid to the study of the structural characteristics and of the physical properties of final products. It has been established that the product phase presents an extensive metastable behavior resulting in the formation of disordered BCC solid solutions or paramagnetic amorphous phases at 300 K depending on the Cr composition and on the preparation procedure.…”

“…Murugesan et al [7] also reported that Fe x Cr 1Àx become paramagnetic for xp0:53 after long time milling. However, Fnidiki et al [11][12][13] have shown that MA Fe 60 Cr 40 is paramagnetic at 300 K due to the effect of residual oxygen and nitrogen. They focus on the effect of significant amounts of O 2 and N 2 on the properties of the as-milled alloys and insist on the importance of controlling the amounts of residual gases [14].…”

Structural evolution in nanocrystalline Fe-10 Wt pct Cr alloy powder produced by mechanical alloying—An atomic-force microscopy study

“…The obtaining of the solid solution of Fe-Cr in powders of mean composition of wt pct Cr milled for 65 and 100 hours, respectively, has been found also through the MS method. [13,14] Due to the extreme thinning down of the individual lamellae of the original Fe and Cr particles or their solid solutions, mechanically milled individual granules are expected to have a nanoscale substructure within their lamellae through which an enhanced diffusion can occur, even at lower temperatures. The temperature of granules during their mechanical milling is also expected to rise, due to the severe plastic strain occurring in the material under the dry-milling environment in argon atmosphere.…”

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

“…Results depicting the Debye temperature obtained with the Mӧssbauer spectroscopy (MS) on a series of nanometer-sized Fe 100-x Cr x alloys (0  x  84), hereafter called n-Fe 100-x Cr x , obtained by mechanical alloying (MA) are reported in this paper. Although n-FeCr alloys prepared by MA were often studied by MS e. g. [13][14][15][16][17][18][19][20][21][22], there is not, to our best knowledge, such study on the Debye temperature known in the available literature.…”