Melt-spun Amorphous Ribbons Research Articles

Properties of amorphous magnetic materials by magnetic force microscopy

The aim of this work has been to show and analyze the domain structure of different amorphous magnetic materials by means of magnetic force microscopy (MFM). The following samples are successfully imaged: amorphous and devitrified melt-spun ribbons, amorphous electrodeposited microtubes which have a giant magneto-impedance effect, and sputtered films with a modulated stress-induced magnetic anisotropy. A correlation between the MFM images and the magnetic characteristics obtained from hysteresis loop measurements has been found.

Magnetic behavior of Nd/sub 50/Fe/sub 40/Al/sub 10/ bulk amorphous alloys

The temperature and thickness dependence of the hysteresis loop, magnetization, coercive field, and AC-susceptibility of melt-spun amorphous ribbons and amorphous cast rods of the composition Nd/sub 50/Fe/sub 40/Al/sub 10/ were measured between 5 and 300 K. The large values of the coercivity are ascribed to the existence of very small magnetic clusters dispersed in the amorphous matrix. The Mossbauer spectra can be fitted to two Fe sites with magnetic moments ranging from 1.47 to 2.00 /spl mu//sub B/.

Production of bulk materials of an Nd/sub 4/Fe/sub 77.5/B/sub 18.5/ alloy and their magnetic properties

Amorphous melt-spun ribbons of an Nd/sub 4/Fe/sub 77.5/B/sub 18.5/ alloy were consolidated into bulk materials by shock compaction. The resultant bulk materials showed a low coercivity as expected for amorphous Nd-Fe-B materials. Heat treatment of the bulk materials above the crystallization temperature resulted in the formation of metastable Fe/sub 3/B phase together with Nd/sub 2/Fe/sub 14/B phase. The resultant bulk magnets showed a coercivity as high as 2.7 kOe as was the case for the annealed melt-spun ribbons.

The influence of coherent ticu plate-like precipitates on the thermoelastic martensitic transformation in melt-spun Ti 50Ni 25Cu 25 shape memory alloys

Amorphous melt-spun ribbons with the composition Ti 50Ni 25Cu 25 were heat-treated for various times above, near or below the crystallization temperature in order to achieve three different states concerning the quantity of precipitates. In detail: homogenized material without precipitates as well as with a moderate and a high density of precipitates, respectively. The thermoelastic transformation behavior and the arising microstructures were characterized by means of differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Precipitates appeared in form of thin coherent TiCu plates on {100}-planes of the parent B2-phase during isothermal heat-treatments. Especially, long-term annealing led to formation of rectangular cell structures as a result of densely precipitated plates. As to this microstructure, the peak form of the transformation curves was broadened and the transformation temperatures were lowered. A thermodynamic description is proposed elucidating the observed transformation behavior. The potential reasons, that is, internal stresses, grain size effect, decomposition, ordering/disordering, are discussed.

Induced anisotropy and magneto-impedance measurements in Fe 73.5Nb 3Cu 1Si 13.5B 9 nanocrystalline alloys

The effect of induced magnetic anisotropy on GMI has been studied in Fe 73.5Nb 3Cu 1Si 13.5B 9 melt-spun amorphous and nanocrystalline ribbons. The amorphous-to-nanocrystalline transformation has been induced by means of furnace annealing and DC joule heating. The correlation between average magnetic anisotropy calculated from quasi-static hysteresis loops and GMI will be discussed in detail.

Self-Diffusion in Nanocrystalline Fe and Fe-Rich Alloys

The present work aims at a comparison of the self-diffusion behaviour of nanocrystalline (n-)Fe produced by cluster condensation and compaction with that of Fe-rich n-alloys made by crystallization of melt-spun amorphous ribbons. In cluster-synthesized Fe (relative density higher than 91 %), a decrease of the (59)Fe tracer diffusivity upon annealing indicates interface relaxation. The diffusion coefficients in the relaxed grain boundaries are similar to those extrapolated from high-temperature data of conventional grain boundaries. Substantially lower interface diffusivities in crystallized n-Fe(90)Zr(10) and n-Fe(90)Zr(7)B(3) presumably arise from residual intergranular amorphous layers. Due to the reduced amorphous fraction, in n-Fe(90)Zr(10) additional fast diffusion paths exist like in conventional grain boundaries.

Formation of nano-sized Ti 68Fe 26Si 6 icosahedral quasicrystalline phase by rapid quenching and mechanical alloying

Investigation using rapid quenching (RQ) and mechanical alloying (MA) were conducted to produce Ti 68Fe 26Si 6 icosahedral quasicrystals. Subsequent heat treatment was performed on both rapidly quenched ribbons and mechanically alloyed powders in a vacuum furnace under various heat treatment conditions of temperature ranging from 440 to 900°C with a constant heating rate of 10°C/min and holding time up to 30 h. The amorphous phase of Ti 68Fe 26Si 6 ribbon was successively achieved by RQ for the first time from the present investigation. During the heat treatment, the icosahedral quasicrystalline phase was transformed from the melt-spun amorphous ribbon at the glass transition temperature of 430°C and remained up to approximately 520°C. The quasicrystalline phase, however, was somewhat difficult to be obtained from heat treatment of the Ti 68Fe 26Si 6 powder milled for 5 h under the present experimental conditions.

High-frequency giant magnetoimpedance in joule-heated Co-based amorphous ribbons and wires

The giant magnetoimpedance (GMI) effect in Co 68.25Fe 4.5Si 12.25B 15 melt-spun amorphous wires and ribbons was studied in the microwave region ( 45 MHz≤f≤6 GHz ). Selected samples were submitted to dc joule-heating in vacuum, exploiting the heat released to the sample by a dc electrical current flow, to induce circular and transverse magnetic anisotropy. The high-frequency impedance was measured using a technique based on the S-parameter measurements of a specific transmission line by means of an automatic vectorial network analyser. Annealed materials, either in wire or ribbon form, display a linear increase of Δ Z/ Z ratio with the applied magnetic field up to reaching a maximum (i.e. Δ Z/ Z≈60% at H≈400 A/m) at low field values.

Highly corrosion-resistant Ni-based bulk amorphous alloys

Bulk amorphous Ni-Nb-Ta-P alloys were successfully prepared by copper mold casting method. The addition of tantalum is effective in decreasing the corrosion rate. The corrosion rates of the alloys containing certain amounts of tantalum are more than four orders of magnitude lower than that of nickel metal and are almost equivalent to that of tantalum even in aggressive 12 M HCl open to air at 30°C. They are spontaneously passive and are characterized by immune to pitting by anodic polarization. The corrosion behavior of the bulk amorphous alloys is almost the same as corresponding melt-spun amorphous alloy ribbons.

Investigations on the Magnetic Properties of High-Coercivity (Nd1−xFex)90Al10 Bulk Amorphous Alloys

ABSTRACTBulk rods with diameters up to 3 mm prepared by suction casting and respectively mould casting and melt-spun amorphous ribbons with thicknesses in the range 25 – 150 μm with compositions Nd90−xFexAl10 (x = 35; 40; 45; 50) were investigated by XRD, DSC and magnetic measurements in the temperature range 5 – 600 K. The microstructure and magnetic properties are strongly dependent on the cooling rate, preparation process and Fe content. The large values of the coercive field, which amount to 320 kA/m in the as-cast state as well as the increase with decrease of the temperature and cooling rate result from the formation of very small metastable or nonequilibrium magnetic clusters.

Ｄｉｄｙｍｉｕｍ‐Ｆｅ‐Ｃｏ‐Ｎｂ‐Ｂ系交換スプリング磁石の磁気特性

Amorphous melt-spun ribbons of Didymium-Fe-Co-Nb-B alloys were prepared by the single-roller rapid-quenching method. The effects of the composition, wheel velocity, and heat treatment on the magnetic properties were investigated. Amorphous Didymium9-Fe76Co8Nb1B6 ribbons prepared at a wheel velocity of 20 m/s were crystallized by heat treatment, and the optimum heat treatment condition was found to be 625°C for 5 min, in which case the value of (BH)max was 147.3 kJ/m3. The temperature coefficients of Br and HcJ for ribbons of crystallized Didymium9-Fe76Co8Nb1B6 alloy were α(Br)= -0.087%/°C (reversible) and α(HcJ)= -0.416%/°C (irreversible), respectively. The value of (BH)max for a compression molded Didymium9-Fe76Co8-Nb1B6 isotropic bonded magnet prepared by using the ribbons annealed at 625°C for 5 min was 79.7 kJ/m3.

Pr-Fe-Co-Nb-B系交換スプリング磁石の磁気特性

The amorphous melt-spun ribbons of Pr-Fe-Co-Nb-B system alloys were prepared by single roller rapid-quenching method. The effect of composition, wheel velocity and heat-treatment on the magnetic properties were investigated. The amorphous Pr9Fe76Co8Nb1B6 ribbon prepared at a wheel velocity of 15.0 m/s were crystallized by heat-treatment, and the optimum heat-treatment condition was found to be at 700°C for 0 min, then the value of (BH)max was 146.2kJ/m3. The temperature coefficients of Jr and HcJ for the ribbons crystallized from the amorphous Pr9Fe76Co8Nb1B6 alloy were α(Jr)=-0.05%/°C (reversible) and α(HcJ)=-0.45%/°C (irreversible), respectively. The value of (BH)max for the compression molding Pr9Fe76Co8Nb1B6 isotropic bonded magnet prepared by using the ribbons annealed at 700°C for 0 min is 84.5kJ/m3 and the density is 6.1Mg/m3.

The temperature dependence of coercivity in nanocrystalline Nd–Fe–B–(TiC) magnets

TiC additions to Nd2Fe14B have been shown to enhance the control of microstructure and greatly modify the solidification behavior of the alloy. The temperature dependence of the coercivity, Hci, of the Nd2Fe14B+xTiC(0<x<6 at. %) is important for both technical applications and a comprehensive understanding of the coercivity mechanism. In addition, by studying the onset of coercivity as a function of the annealing temperature of amorphous ribbons the activation energy for crystallization may be determined. Amorphous melt-spun ribbons with x=0, 2, 3, and 6 were annealed isothermally in an Ar atmosphere at temperatures near, above and below the crystallization temperature. The activation energies Ea were determined by fitting the dependence of the coercivity as a function of annealing time and temperature to the Arrenius’ equation and found to be 18–25 kcal. The coercivity distribution functions of micro volumes of magnets were created using demagnetization and reversible magnetization curves that allowed the correlation of the coercive force with nanostructure. Maximum Hci of up to 15 kOe (3 at. % TiC) is achieved for an average grain size of 20–40 nm. The temperature dependencies of coercivity of stoichiometric Nd2Fe14B ribbons without and with additions TiC have similar character in temperature range (250–400 K) for all samples. The coercivities for nanocrystalline Nd2Fe14B magnets with TiC are more than for stoichiometric material.

Bulk Amorphous Fe–Ga–P–B–C Alloys with a Large Supercooled Liquid Region

Amorphous Fe 75 Ga 5 P 12 C 4 B 4 alloy rods were prepared in the diameter range up to 1.0 mm by copper mold casting. The glass transition temperature (T g ), supercooled liquid region (ΔT x (= T x - T g )) and reduced glass transition temperature (T g /T m ) of the amorphous alloy rods are 731 K, 37K and 0.61, respectively, in agreement with the results for the corresponding melt-spun amorphous alloy ribbon. The Curie temperature (T c ), saturated magnetization (I s ), coercive force (H c ) and saturated magnetostriction (λ s ) of the melt-spun amorphous ribbon are 622 K, 1.28T, 1.6 A/m and 19.6 × 10 -6 , respectively, in which the T c and I s are nearly the same as those for the amorphous alloy rod with a diameter of 0.5 mm. The simultaneous achievement of high T g /T m , large ΔT x and good soft magnetic properties for the simple Fe-based alloy system is promising for the future development of bulk amorphous Fe-based soft magnetic alloys.

Local Magnetic Structure and Magnetic Properties of Nd50Fe40Si10-xAlx Bulk Glassy Hard Magnets

AbstractThe large values over 300 kA/m at room temperature were found for the coercive field of Nd50Fe40Si10−xAlx (x = 0; 10) amorphous melt-spun ribbons and cast rods. The dependence of the coercive field on the thickness and the preparation method, namely the cooling rate, is ascribed to the existence in the amorphous matrix of very small ferromagnetic clusters, which approach of a single magnetic domain. Coercivity increases substantially up to 600 kA/m by decreasing the temperature down to 200 K, although the measurements are carried out in low fields (up to 800 kA/m). The Mässbauer spectra can be fitted to two Fe sites with magnetic moments ranging from 1.25 to 2.20νB depending on the additional element.

A New Method for Producing Amorphous Alloy Wires

A rotating disk casting has been developed as a new method of producing an amorphous alloy wire. The rotating disk, which is made of copper, has a semicircular groove on its upside surface. The amorphous alloy wires with large diameters from 0.5 to 1.5 mm in the Zr-Al-Ni-Cu alloy system with high glass-forming ability have been prepared by the new method. The cross-section of the wires is nearly circular. because the melt is quenched to an amorphous state at the contact with an inner surface in the groove of the rotating disk. The cast amorphous alloy wires exhibit the same thermal stability and mechanical properties as those for the melt-spun amorphous alloy ribbon with the same composition. The formation of the amorphous alloy wires with large diameters is attributed to the high glass-forming ability of the alloy. In any event, the success of forming amorphous alloy wires by the present casting method is important for the future extension of application fields ol amorphous alloys.

329 複合機能化センサ・アクチュエータ薄板・繊維要素材料作成のための液体急冷加工プロセス装置開発とその材料特性(OS 多機能・複合機能化への材料協調設計)

The rapid-solidification machine to produce the composite fillers having multi-functional material elements of sensor/actuator was developed. This machine which is called as "melt-spinning and melt extraction using a high frequency and an arc furnace" can make the fine fibers (diameter=20〜100 μm) as well as foils(thickness=30〜60μm) with unique microstructures by rapid-solidification. Shape memory alloy(SMA) ribbons of TiNi and forromagentic FeNi SMA fibers could be produced. Moreover, Al_<85>Ni_<10>Ce_5, Ti_<40>Zr_<10>Cu_<50> and Zr_<65>Al_<10>Cu_<15>Ni_<10> amorphous wires were produced by more rapid-solidification speed. The wires have a circular cross section and a smooth peripheral surface, but small flaws are observed on the surface. The structure of the amorphous alloy wires is nearly the same as that of the melt-spun amorphous ribbons by SEM observation and X-ray diffraction analysis. The shape memory effect and mechanical properties were improved by rapid-solidification.

Ｎｄ‐Ｆｅ‐Ｃｏ‐Ｃｕ‐Ｎｂ‐Ｂ系交換スプリング磁石の磁気特性に及ぼすＰｒ置換の影響

Amorphous melt-spun ribbons of Nd-Pr-Fe-Co-Cu-Nb-B system alloys were prepared by the single-roller rapid-quenching method The effects of composition, wheel velocity, and heat treatment on their magnetic properties were investigated. Amorphous Nd2.7Pr6.3Fe75.5Co8Cu0.5Nb1B6 ribbons prepared at a wheel velocity of 12.5 m/s were crystallized by heat treatment, and the optimum heat-treatment condition was found to be 675 °C for 0 min,then the value of (BH)max was 156.16 kJ/m3. The temperature coefficients of Jr and HcJ for the ribbons crystallized from the amorphous Nd2.7Pr6.3Fe75.5Co8Cu0.5Nb1B6 alloy are α (Jr) = −0.036 % /°C (reversible) and α (HcJ) = −0.46 %/°C (irreversible), respectively.

Structural and magnetic properties of the nanocrystalline alloy Fe86Zr7Cu1B6

A detailed study on the nanocrystallization and its correlation with the attractive soft magnetic properties of the alloy Fe86Zr7Cu1B6 (at %) is presented. Melt-spun amorphous ribbons were submitted to Joule heating for a short time interval (ta=50 s) with different direct current values. The electrical resistance measured during heating showed strong variations associated with the nucleation and growth of α-Fe nanocrystals. From x-ray diffraction line profile analysis we obtained the average grain size, crystalline volume fraction, grain size distribution function, and lattice distortions for different annealing currents. The results display an excellent agreement with the magnetic characterization (ac initial permeability and dc hysteresis loops), showing that the optimum soft magnetic behavior is associated with the formation of about 50% in volume of the α-Fe nanophase. The extended x-ray absorption fine structure (EXAFS) technique was applied to study the evolution of the short-range ordering around Fe atoms. EXAFS spectra also showed the evolution from a disordered Fe environment to the bcc crystalline arrangement. The onset of crystallization determined from both techniques is slightly different, indicating that the nanocrystallization begins at the surface of the studied samples.

Exchange coupled R2(Fe,Co,Nb)14B/(Fe,Co) (R=Nd,Pr) and Sm2(Fe,Co,Cr)17C2/(Fe,Co) nanocomposite magnets

Abstract Fe-rich exchange coupled nanocomposite R 8 (Fe,Co,Nb) 86 B 6 (R=Nd, Pr) (consisting of hard 2:14:1 and soft α-Fe(Co) phases) and Sm 2 (Fe,Co) 15 Cr 2 C 2 magnets (consisting of hard 2:17 and soft α-Fe(Co) grains) have been studied. In both systems the nanocomposite hard/soft microstructure is obtained by crystallizing the as-made amorphous melt-spun ribbons. The coercivity is found to depend mainly on the grain size of the soft phase which is very sensitive to the sample composition and annealing conditions. In the R–(Fe,Co,Nb)–B system, it is found that substitution of Nb for Fe significantly decreases the grain size of the α-Fe(Co) and increases the coercivity of the magnets. Substitution of Co for Fe increases the grain size and results in a dramatic decrease of coercivity. Increasing the B content of Co-substituted samples leads to a partial recovery of the coercivity. Magnetic properties M r / M s =0.7 and H c =6.5 kOe have been obtained for Pr 8 ((Fe 0.5 Co 0.5 ) 0.94 Nb 0.06 ) 82 B 10 . In the Sm 2 (Fe,Co) 15 Cr 2 C 2 system, it is found that a higher annealing temperature combined with a shorter annealing time leads to a higher coercivity. The optimum annealing condition is at 900°C for 1 min where the highest coercivity of 12.1 kOe is obtained. The grain size of α-Fe in annealed ribbons becomes much smaller with Co substitution, leading to a stronger exchange coupling between the 2:17 and α-Fe phase. A significant enhancement in the Curie temperature of the 2:17 phase is observed in these magnets as compared to their parent alloys due to the exchange coupling effect between the 2:17 phase and the Fe(Co) phase.