Mössbauer Study on Atomic Reordering of Cold-Worked Iron-Aluminum Alloys

Abstract

The process of atomic reordering of cold-worked Fe-Al alloys in the composition range from about 25 to 35 at%Al has been investigated by means of Mossbauer spectroscopy. Mossbauer spectra for the specimens filed and subsequently annealed were taken at each stage of annealing and analyzed to obtain the distribution of internal magnetic field in the alloys. Furthermore, for the alloy with 24.9 at%Al information on the neighbor configurations of constituent atoms was successfully able to be obtained directly from the Mossbauer spectra by assuming the Gaussian distribution function of internal magnetic field acting on iron atoms with various numbers of iron neighbors, and a detailed process of reordering during annealing was clarified.The ordered alloy with the DO3 type, which is either weakly magnetic or nonmagnetic depending on the composition, became strongly magnetic by cold working. The alloy as-filed was much complicated in structure, and the atomic configuration seemed to be distinctly different from that of the thermally disordered state. The alloy reordered very slowly in the course of annealing by way of the perfect disorder and the B2 type of order. The ordered alloy with the B2 symmetry, which is nonmagnetic, was partially disordered by cold working and changed into a weakly magnetic state. The alloy reordered promptly to its initial state by a relatively low temperature annealing.

Ordering effects in the Fe-Al system

“…The magnetic behaviour depends strongly upon the phase state and upon the atomic arrangement i.e. ordered, partially ordered or disordered structures [2,32,33,36,38,39,42,49,19]. at % Al (after Allen [27] The specific heat has been reported by Beck et a1.…”

“…Physique 44 (1983) ; however there is now a qualitative agreement between different studies on the nature of the phases and on the order-disorder transitions in the Fe rich regions of the diagram [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. In fact this diagram is very complex and shows some very unusual features in metallurgical systems [15][16][17].…”

Short-range order in "disordered" aluminum solid solutions in α-iron

“…The phase diagram of the Fe-Al system has been refined many times over the years, but now there is a qualitative agreement between various studies of the nature of phases and order-disorder transitions in the Fe-rich regions of the diagram [7][8][9][10][11][12][13][14][15][16]. In the low-temperature part of the phase diagram [17,18] up to approximately 20 at.% Al, there is a region of α-phase (structure A2) or a substitutional disordered solid solution.…”

Ближний порядок в "неупорядоченных" твердых растворах алюминия в α-железе

“…Фазовая диаграмма системы Fe-Al многократно уточнялась на протяжении многих лет, однако в настоящее время имеется качественное согласие между раз-личными исследованиями природы фаз и переходов порядок-беспорядок в богатых Fe областях диаграммы [7][8][9][10][11][12][13][14][15][16]. В низкотемпературной части фазовой диаграммы [17,18] примерно до 20 at.% Al имеет место область α-фазы (структура A2) или неупорядоченного твердого раствора замещения.…”