Addition of various elements to equiatomic FeCo alloys and changes in ratio of iron and cobalt have been examined in order to study mechanisms for the improvement of ductility in the alloy. It has been revealed that Fe30Co70, one of the alloys having a different Fe/Co ratio, and alloys having additive elements such as carbon, vanadium, chromium, nickel, niobium, molybdenum, tantalum and tungsten ranging from 0.5 to 2 at %, are effective in improving ductility; whereas aluminium, beryllium, boron, copper, gold, manganese, silver, silicon, titanium and zirconium are ineffective. A common feature is found in the effective alloying elements: the elements combine with cobalt to form an Co3X type compound that can be produced only by diffusion; for instance, Co3C, Co3V, Co3Cr, Co3Ni, Co3Nb, Co3Mo, Co3Ta and Co3W. It is suggested, as a way of explaining this common feature, that as a result of the formation of the Co3X compound, the zones, difficult to cause the order lattice may be produced around the compound particles, and thus resulting in ductility.

Effect of additive elements on cold workability in FeCo alloys

Effect of structural changes based on heat treatments upon the ductility of an FeCo-2V alloy has been studied. The ductility does not always result from the martensitic transformation, but it always results from the ferritic structure which is composed of large and heterogeneous grains, whenever the specimens are quenched from a temperature of the ferritic region. In the case of the specimens heat treated at and quenched from a temperature where two phases can coexist, the ductility is strongly affected by the uniformity of the mixed structure obtained by such a treatment. The ductility of the mixed structure is improved by combinations of various heat treatments. After ordering, however, all specimens treated have never shown any ductility. The distribution of the precipitates occurring during ordering have shown a remarked difference between as-cast and as-cold-rolled specimen; the former is dilute, while the latter is dense. The composition of the individual particles extracted from the samples which are satisfactorily aged are shown to be about 64Co-21V-15Fe on average. Following to the information, a possible mechanism of improving the ductility of the alloys is argued on a model of local concentration-disordered zones.

Structures and mechanical properties of an FeCo-2V alloy

Dry reed contacts typically fall into two categories, the nonself-latching and the self-latching types. Historically, the nonself-latching was the first developed and Fe-Ni alloys have found wide acceptance as the reed material. More recently, the self-latching contact has received widespread attention from the communications industry, motivated by potential reductions in physical size and energy consumption. This has stimulated studies into new magnetic alloy development and into material processing modifications, on both newly developed as well as previously known alloys, to meet the stringent properties requirements. The emphasis of this review is on the self-latching contact focusing on its requirements, the magnetic materials which have the potential to meet these requirements, and the sometimes intricate processing steps which have been developed to realize the potential. Alloys in the Co-Fe-Nb, Co-Fe-V, Co-Fe-Ni-Al, and several other families which are principally precipitation-type permanent-magnet materials are considered.

Magnetic materials for dry reed contacts

The effects of the combination of cold rolling and heat treatment upon mechanical and magnetic properties have been examined for the FeCo-based alloys with additive elements such as carbon, vanadium, chromium, molybdenum, tungsten, tantalum, niobium, and nickel. It is revealed that whenever alloys including such elements are subjected to cold rolling the yield strength can be raised to between 100 and 200 kg mm−2, and that cold rolling is effective in both strengthening and in improving soft magnetic properties, even when cold rolling is followed by annealing or ageing. This suggests that these alloys can be used for lessening the weight of parts which are used as soft magnetic materials, although their properties will depend on the combinations of cold rolling and heat treatments, and/or on the added elements and the control of their amount.

A possibility for developing high strength soft magnetic materials in FeCo-X alloys

Influence of thermal treatments on the mechanical properties of an FeCoV alloy (remendur)

The variations in coercivity, remanence, and microstructure for 2\frac{1}{2} hour aging anneals between 300°C and 1000°C on an Fe/Co/3% V alloy have been determined. Additionally, the effects of varying aging times for temperatures between 885°C and 925°C have been analyzed. Hysteresis parameters and optical microstructures were characterized on wire samples which had been either cold worked by stamping or remained undeformed prior to the aging anneals. Results show that the alloy exhibits maximum magnetic hardness in its initial cold worked or undeformed conditions. Aging anneals produce a general decrease in magnetic properties with increasing temperatures to 700°C. However, the deformed material exhibits a secondary maximum for aging temperatures between 590°C and 610°C. For anneals above 800°C magnetic parameters again increase as a two-phased, duplex BCC (α 1 + α 2 ) structure is developed. By varying the aging time for anneals that produce this duplex structure, a level of coercivity comparable to that achieved for a 600°C anneal was attainable. However, a comparable level of remanence and, thus, a similar squareness ratio, could not be produced with the duplex structures developed by aging near 900°C.

J. Bennett

Papers

Influence of annealing temperature and time on hysteresis parameters and microstructure of an Fe/Co/V alloy