Richard T. Fingers

Application of high temperature magnetic materials

The trend in both military and commercial markets for greater affordability has prompted the electromechanical designer toward higher speed and higher operating temperature devices. New magnetic materials are essential for the success of many of these power generation, distribution, and utilization systems. This manuscript briefly describes some of the applications for advanced high temperature magnets.

Synthesis and magnetic behavior of SmCo5(1−x)Fex nanocomposite magnets

SmCo5(1−x)Fex (x=0.2, 0.4, 0.6, and 0.7) nanocomposites were synthesized by ball milling a mixture of SmCo5 and nanosize iron powders. Composites were made using different kinds of soft ferromagnetic phase nanoparticles, either α-Fe crystallized from amorphous iron generated by sonochemical decomposition of Fe(CO)5, or acicular metallic iron particles with an average length of 200 nm and average diameter of 18 nm. After milling the powder mixtures were compacted by hot isostatic pressing at 3000 psi for ∼5 min at a temperature of 530–570 °C. The compacted solids were magnetically characterized between 5 and 300 K. Hysteresis loop measurements and recoil measurements for the (SmCo5)0.8/acicular-Fe0.2 composite show stronger magnetic coupling when compared with the properties of (SmCo5)0.8/amorphous-Fe0.2, am-Fe coated SmCo5, and pure SmCo5 powders alone.

Effect of aging on magnetic properties of Hiperco® 27, Hiperco® 50, and Hiperco 50 HS® alloys

We started a long-term aging study that will identify the aging related changes in magnetic, mechanical, and electrical properties of three Fe–Co soft magnetic alloys. We performed the aging at a temperature of 773 K and in two different environmental chambers, argon gas and air, in order to determine the oxidation resistance of these alloy laminates as well. Each aging batch includes creep and yield stress test specimens, rings for ac magnetic measurements and specimens for electrical resistivity and microstructural analysis. Here we report the change in total power losses after 2000 h annealing up to frequencies of 2 kHz for the Hiperco® 27, Hiperco® 50, and Hiperco® 50 HS alloys. We also report the temperature dependence of total power losses between 298 and 773 K for these alloys.

Microstructural and magnetic observations of compacted FECOV nanoparticles

One attempt to improve core loss of electromagnetic machines is to utilize nanocrystalline alloys, which are predicted to have extremely soft magnetic properties. High magnetic saturation values and high Curie temperatures make iron-cobalt alloys attractive for such applications. In this work iron-cobalt-vanadium nanopowders were synthesized and compacted. The coated particles were characterized and examined in both the powder and compacted states. Higher than expected coercivities are reported and may be due to the inhomogeneous microstructure resulting from interactions with the vanadium.

Structure and magnetic properties of Sm(Co1−xZrx)y alloys (x=0.03–0.05,y=12–15) and melt-spun Sm(Co,Fe,Zr,Cu,Ga,B)12 material

Alloys with nominal compositions of Sm(Co1−xZrx)y (x=0.03–0.05, y=12–15) were synthesized by arc melting and characterized in the temperature range of 10–1473 K and with a magnetic field up to 5 T. Near-single-phase materials with Th2Ni17 structure were formed in the as-cast alloys with x=0.05. Similar to Ti, Zr also stabilizes the Th2Ni17 structure. Hard magnetic properties with Tc∼1142–1179 K, Ms∼110–123 emu/g, and Ha∼63–86 kOe at 300 K have been observed. An alloy with a nominal composition of Sm(Co0.75Fe0.1Zr0.05Cu0.08Ga0.01B0.01)12 was also prepared by melt spinning. The melt spun materials were nanostructured in nature and magnetically hard in the as-spun states. Hci∼10 kOe, Bs∼9.5 kG, and Hci∼27 kOe, Bs∼9.8 kG were obtained at 300 and 10 K, respectively. The effects of the heat treatment conditions on magnetic properties of both alloys and ribbon will be also discussed.

Structure and magnetic properties of Sm(Co/sub bal/Fe/sub x/Ti/sub 0.05/)/sub 9.66/ alloys (x=0-0.57) and Sm(Co/sub 0.66/Fe/sub 0.19/Ti/sub 0.05/Cu/sub 0.1/)/sub 9.66/ magnets

Potential permanent magnetic materials with compositions of Sm(Co/sub bal/Fe/sub x/Ti/sub 0.05/)/sub 9.66/ (x=0-0.57) have been synthesized and characterized in the temperature range of 10-1473 K and at fields up to 5 T. The experimental results show that near single phase materials with Th/sub 2/Ni/sub 17/ structure were formed in Sm(Co/sub bal/Fe/sub x/Ti/sub 0.05/)/sub 9.66/ alloys after splat quenching from 1473 K. The Ti atoms play an important role in stabilizing the Th/sub 2/Ni/sub 17/ structure for the 3d (transition metal) rich nonstoichiometric 2-17 compounds. Encouraging hard magnetic properties with T/sub c//spl sim/890-1066 K, M/sub s//spl sim/10.8-13.7 kG, H/sub a//spl sim/30-125 kOe at 300 K were observed in Sm(Co/sub bal/Fe/sub x/Ti/sub 0.05/)/sub 9.66/ alloys. Both Sm(Co/sub 0.66/Fe/sub 0.19/Ti/sub 0.05/Cu/sub 0.1/)/sub 9.66/ sintered and melt-spun powder magnets with 4/spl pi/M/sub s//spl ges/10 kG were fabricated. A strong domain wall pinning behavior with H/sub c//spl sim/1.6 kOe at RT and H/sub c//spl sim/4.3 kOe at 10 K was observed. The effect of different heat treatment conditions on the phase formation of Sm(Co/sub bal/Fe/sub x/Ti/sub 0.05/)/sub 9.66/ alloys was also discussed.

Structure and magnetic properties of Sm(Co/sub bal/Fe/sub x/Zr/sub 0.05/Cu/sub 0.08/Ga/sub y/B/sub z/)/sub 12/ alloys

3d-rich alloys and their melt-spun materials with nominal compositions of Sm(Co/sub bal/Fe/sub x/Zr/sub 0.05/Cu/sub 0.08/Ga/sub y/B/sub z/)/sub 12/ (x=0.1-0.41, y=0-0.01, z=0.01-0.02) were synthesized and characterized in the temperature range of 10-1473 K and at fields up to 5 T. The main phase of the as-cast alloys was formed in a Th/sub 2/Ni/sub 17/ type structure, exhibiting a strong uniaxial anisotropy. As a result, encouraging hard magnetic properties with T/sub c/=995-1086 K, H/sub a/=40-115 kOe, M/sub s/=10-12.8 kG at 300 K, and H/sub a/=60-180 kOe, M/sub s/=10.4-13.6 kG at 10 K were observed in the as-cast alloys. The melt-spun materials are nano-structured in nature and magnetically hard, even in the as-spun state. The following hard magnetic properties were observed: H/sub ci/=7-10 kOe, 4/spl pi/M/sub s/=9.4-11.7 kG, at 300 K, and H/sub ci/=17-27 kOe, 4/spl pi/M/sub s/=9.6-12.1 kG, at 10 K. The highest (BH)/sub max//spl sim/9.8 MGOe at 300 K was obtained from the Sm(Co/sub bal/Fe/sub 0.31/Zr/sub 0.05/Cu/sub 0.08/B/sub 0.02/)/sub 12/ ribbon material. A Henkel plot analysis indicates the existence of a strong exchange-coupling interaction between the magnetically hard and soft phases in these ribbon materials. The effects of adding Ga, B, and Fe on the magnetic properties will be discussed.

Effect of tensile stress and texture on magnetic properties of FeCo laminates

AC and dc magnetic properties and related losses of FeCo alloy sheet samples have been determined under applied tensile stress. Heat-treated strips of alloys Hiperco 50 Hiperco 50-HS and Hiperco 27 with three different orientations (0/spl deg/-45/spl deg/-90/spl deg/) with respect to the rolling direction were tested under tensile stresses up to 200 MPa. In our earlier work, we reported the effect of the compressive stress on the same alloy compositions . Unlike compressive stress, tensile stress decreased the coercivity and increased remanence of the alloys. For the 90/spl deg/-oriented Hiperco 50 alloy with a coercivity of 1.12 Oe under no applied stress, the minimum coercivity of 0.29 Oe occurred at about 100 MPa. The effect of tensile stress on the remanence was most pronounced in the Hiperco 50 HS samples. A gradual decrease in the coercive field of the three Hiperco 50 HS samples was observed up to 200 MPa. On the other hand, a minimum at 25 MPa is observed for the coercivity of Hiperco 27 samples. At the same tensile stress, the remanence ratio had a maximum. The 0/spl deg/-oriented sample exhibited the lowest core loss value of the Hiperco 27 samples.

Magnetic properties of Sm(Co/sub bal/Fe/sub 0.31/Zr/sub 0.05/Cu/sub 0.04/B/sub x/)/sub z/ alloys and their melt-spun materials (x=0.02--0.04,z=7.5--12)

Cast alloys and melt-spun ribbons with nominal compositions of Sm(Co/sub bal/Fe/sub 0.31/Zr/sub 0.05/Cu/sub 0.04/B/sub x/)/sub z/ (x=0.02-0.04,z=7.5-12) have been synthesized and characterized in a temperature range of 10-1273 K and at fields up to 5T. The main phase in the as-cast alloys exhibited a Th/sub 2/Ni/sub 17/ type structure, with a strong uniaxial anisotropy. Minor phases with a TbCu/sub 7/ and/or CaCu/sub 5/ structure emerged as z (3d/R) decreased. As a result, the anisotropy field (H/sub A/) increased from 67 to 120 kOe, while 4/spl pi/M/sub s/ fell from 12.8 to 10.5 kG at 300 K when z was decreased from 12 to 7.5. For melt-spun ribbons, they are nano-structured in nature and magnetically hard, even in the as-spun state. By lowering the value of z(3d/R) and raising the B content, a finer microstructure and a higher H/sub ci/ were obtained. Hard magnetic properties of H/sub ci/=4.9-12 kOe, 4/spl pi/M/sub s/=9.0-12.0 kG at 300 K have been obtained from ribbon samples. Among them, Sm(Co/sub bal/Fe/sub 0.31/Zr/sub 0.05/Cu/sub 0.04/B/sub 0.02/)/sub 10/ ribbon showed the highest (BH)/sub max/ of 10.8 MGOe at 300 K. A Henkel plot analysis suggested the existence of exchange-coupling interaction between the magnetically hard and soft phases in the ribbon materials.

Soft magnetic powder-core composites of Fe90Zr7B3 and Fe49Co21Al5Ga2P9.65C5.75B4.6Si3 alloys

Amorphous and nanocrystalline alloys in ribbon form exhibit excellent soft magnetic properties, but their forms are limited to tape wound cores. Complex shapes require the implementation of a powder metallurgical approach resulting in reduced permeabilities. The present study investigates Fe-based Fe90Zr7B3 (C1) and Fe49Co21Al5Ga2P9.65C5.75B4.6Si3 (C2) melt-spun ribbons as precursors for compacted powder cores. Single-roller melt spinning of C1 produced partially crystallized structures while C2 resulted in amorphous ribbons. Annealing studies were carried out based on the crystallization temperatures of various phases extracted from M(T) measurements. In ribbon form and under optimum annealing conditions, C1 revealed a 1.88T saturation flux density (Bs) and 44A∕m coercivity (Hc), while C2 exhibited a Bs of 0.78T and Hc of 2.4A∕m.