An increase of structural order parameter in Fe–Co–V soft magnetic alloy after thermal aging

Abstract

Alloys of Fe49Co49V2 (Hiperco Alloy 50) (Hiperco is a registered trademark of CRS Holdings, Inc.), both annealed and thermally aged, were studied using anomalous synchrotron x-ray and neutron powder diffraction. Rietveld and diffraction profile analysis indicated both an increase in the structural order parameter and a small lattice expansion (∼0.0004 Å) after aging at 450 °C for 200 h. In addition, a cubic minority phase (<0.3%) was identified in the ‘‘annealed’’ sample, which increased noticeably (0.3%→0.8%) as a result of aging. The presence of antiphase domain boundaries in the alloys was also revealed. These results directly correlate with the observed changes in the magnetization behavior and challenge the notion that a ‘‘fully’’ ordered Fe–Co alloy demonstrates optimum soft magnetic properties.

Near equiatomic FeCo alloys: Constitution, mechanical and magnetic properties

“…Surprisingly, in a recent investigation on the ageing (200 h at 450°C) of FeCo-2V, Zhu et al [29] report the formation of a primitive cubic second phase, of lattice parameter 2.8278 Å , and although refer to past literature on c 2 , do not comment on the discrepancy with the otherwise accepted structure.…”

Magnetic core loss of ultrahigh strength FeCo alloys

“…4 -7 In the FeCo-based alloys, the desire to retain the B2 phase often resorts to heat treatments of the specimens at high temperatures ͑e.g., 750°C) with slow cooling after processing. 8 The magnetic and mechanical properties reported in the literature are mostly those after high-temperature annealing. 4 -8 Recently, we have developed ultrahigh strength FeCo alloys with a unique combination of high yield strength ͑as much as a factor of 3 higher͒ and excellent ductility by controlling the grain size.…”

Ordering and phase separation in alloys of the Fe–Co system

“…So, the detection of a small volume fraction of the B2 phase in the bulk signifies that the existing situation that the B2 phase can have a determining effect on the magnetic properties of the Fe-Co alloys is contrary to fact. It should be also pointed out that TEM gives no way of detecting any antiphase domains, which have been previously detected by Buckley [9] and Zhu et al [5].…”

“…It is agreed that a fully ordered Fe-Co alloy, attainable through a normal annealing procedure, possesses the optimum soft magnetic properties [4]. That is the reason why a lot of authors have devoted primary attention for the study of B2 ordering in the Fe-Co system [4][5][6][7][8]. Some authors, for example, authors of Ref.…”