Pekka Ruuskanen

Influence of heat treatment on the magnetic and piezomagnetic properties of amorphous and nanocrystalline Fe64Ni10Nb3Cu1Si13B9 alloy strips

FINEMET type alloy with substitution of 10 at.% of iron by nickel is studied from the point of view of the influence of the nanocrystallization process on the magnetic and magnetoelastic properties. Strip-shape samples of Fe 64 Ni 10 Nb 3 Cu 1 Si 13 B 9 amorphous alloy were annealed in vacuum for 1 h in the temperature range of 350-550 °C. Hysteresis loops were measured in order to determine the amount of anisotropy energy and corresponding anisotropy field, and coercive field of each annealed sample. This coercitivity reaches a minimum (about 5 A/m) after annealing at 460°C. Magnetic field dependencies of magnetoelastic properties were also investigated. We have found a maximum value of the ΔE effect and magnetomechanical coupling coefficient of 61% and 0.85, respectively, that are accompanied by a minimum value of the quality factor of about 2 for the sample annealed at 460°C. Such good parameters are related with internal stress relief and structural relaxation of the samples. The subsequent drop of the magnetoelastic coupling coefficient for higher annealing temperatures is related directly with a drop on the magnetostriction value, from (22-26) x 10 -6 to 13 x 10 -6 , due to the formation of a nanocrystalline structure in the samples. On the other hand, ultrasound velocities, measured at magnetic saturation of each sample, increase continuously between 4.9 and 5.6 km/s as the annealing temperature of the sample increases.

Formation of amorphous Fe1−xBx alloys during solid state alloying with hexane

Fe1−x–Bx alloys were synthesized in an argon atmosphere using a high energy ball-mill. The alloyings were also performed in argon with hexane as a process control agent (PCA). With powders milled in argon mixture of amorphous FeB and crystalline FeB and Fe2B phases with nanometer size existed. The amorphous phase content increased with the increase of the boron content. When hexane was used as a process control agent the carbon content of the ball-milled powder was found to increase as a function of the ball-milling time. A maximum carbon content of 37 at.% was measured after 500 h of milling. The increase in the carbon content being caused by the dissolution of the hexane. The dissolved carbon was found to increase the formation of the amorphous phase in the structures. Within a composition range of 0.1≤x≤0.2 a single phase amorphous structure exists. Within a composition range of 0.2<x≤0.5 the structure consists of a mixture of an amorphous phase and crystalline FeB and Fe2B phases. The average Curie temperature of the alloys milled in argon was 780°C, and that of alloys milled with hexane only a little less than 750°C. The onset of the exothermic reaction temperatures during annealing of the powders was about the same, 450°C, for both alloy types. Mossbauer measurements revealed that the carbon does not form carbides but remains in a solid solution within the amorphous matrix.

Elasticity moduli and structure of the Fe73.5Cu1Ta3Si15.5B7 alloy

Abstract Magnetic field dependences of the piezomagnetic dynamics Z d and moduli of elasticity in the Fe73.5Cu1Ta3Si15.5B7 alloy strips in as-quenched state and after annealing for 1 h in vacuum in the temperature range from 400°C to 600°C were studied. The elasticity moduli were changed from 75 to 210 GPa depending on magnetic bias field and annealing temperature. A crystalline structure having nanometer sized crystals was observed after annealing at 500°C.

Piezomagnetic and magnetostrictive properties and structure of Fe-Cu-Nb-Ta-Si-B alloys annealed in vacuum

Abstract Magnetic field dependences of magnetomechanical coupling coefficient and moduli of elasticity in Fe73.5Cu1Nb1Ta2Si15.5B7 alloy in as-quenched state and annealed in vacuum for 1 h at temperatures from 300 to 650 °C were investigated. The maximum changes of the E (ΔE effect), from 102 to 170 GPa, were observed after annealing at 440 °C and from 100 to 165 GPa after annealing at 460 °C. The magnetomechanical coupling coefficient after these heat treatments in the temperature range 440–480 °C was equal to 0.45–0.47. For the-nanocrystalline sample annealed at 560 °C, ΔE was equal to zero, i.e., magnetomechanical coupling vanished. The magnetostriction responsible for these phenomena decreased from about 24 × 10 −6 after annealing for 1 h at temperatures of 400–450 °C, to 17 × 10−6, 6 × 10−6, about 2 × 10−6 and nearly zero after annealings at 475, 500, 525 and 550 °C, respectively. The decrease of the magnetostriction is connected with the formation of the nanocrystalline structure.

Magnetostriction and crystallization of a Fe-Cu-Nb-Si-B alloy annealed in a vacuum from 300 to 650 °C

Abstract The magnetostriction of Fe73.5CU1Nb3Si15.5B7 metallic glass, annealed in a vacuum for l h at temperatures from 300 to 650 °C, was measured using a strain gauge method. The maximum values of the magnetostriction coefficient for technical saturation (at Hmax = ~2.9 kA/m) slowly decreased from approximately 25 ± 2 × 10−6 after annealing at 300 °C, to approximately 21 ± 2 × 10−6 after annealing at 560 °C, and rapidly to about 2 ± 2 X 10−6 after annealing at 600 °C. After annealing at 650 °C, the magnetostriction increased to about 6 ± 2 × 10−6. The decrease in the magnetostriction is connected with an increase in crystallization.

Amorphous and metastable Fe1−xSix alloys and compounds prepared by solid-state synthesis

Abstract Metastable amorphous and crystalline Fe1−xSix alloys and compounds were synthesized in an argon atmosphere with and without hexane, using a solid-state alloying method in a composition range of 0.1

Magnetostrictive and piezomagnetic properties of the Fe73.5Cu1Nb3Si15.5B7 metallic glass annealed in helium

Abstract The effect of different heat treatments on the piezomagnetic properties and magnetostriction of Fe73.5Cu1Nb3Si13.5B9 metallic glass were investigated as a function of the bias magnetic field. The maximum values of the magnetomechanical coupling coefficient were equal to 0.15 for the as-quenched state, and 0.4 and 0.6 after annealing at 510 °C for 1/4 and 1 h, respectively. The magnetostrictive hysteresis loops were measured using the strain gauge method. The values of magnetostriction (A) at a magnetic field equal to about 3 kA/m in all cases were equal to about 22 × 10−6.

Magnetostriction hysteresis loops of annealed Fe73.5Cu1Nb3Si15.5B7 metallic glass strips

Abstract Magnetostriction hysteresis loops of Fe 73.5 Cu 1 Nb 3 Si 15.5 B 7 metallic glass strips annealed in vacuum for 1 h at temperatures ranging from 300 to 650°C were determined using a strain-gauge method. The magnetostriction at H m = 2.8–3.0 kA/m decreased from 25 × 10 −6 after annealing at 300°C to 21 × 10 −6 after annealing at 560°C, to about 2 × 10 −6 after annealing at 600°C, and increased to approximately 6 × 10 −6 after annealing at 650°C. The remanent magnetostriction after annealing from 300 to 560°C increased from 1.35 × 10 −6 to 5.01 × 10 −6 .