Low Wheel Speed Research Articles

Crystallographic alignment and magnetic anisotropy in melt-spun Nd-Fe-B/α-Fe composite ribbons with different neodymium contents

Crystallographic alignment and magnetic anisotropy were studied for Nd xFe 94- x B 6 ( x=8, 9, 10, 11) ribbons prepared via melt-spinning. Effect of Nd content and wheel speed on the crystal structure and magnetic properties of the ribbons was investigated. Both the free and wheel side of the ribbons could obtain strong c-axis crystal texture of Nd 2Fe 14B phase perpendicular to the ribbons surface at low wheel speed, but the texture weakened gradually with the increase of the wheel speed. Increase of Nd content led to better formation of crystal texture in the ribbons, indicating that the α-Fe phase might undermine the formation of crystal texture. Magnetic measurement results showed that the magnetic anisotropy of the ribbons exhibited corresponding behavior with the invariance of the c-axis crystal texture of Nd 2Fe 14B phase in the ribbons, and the coercivity of the ribbons rose with the increase of both Nd content and wheel speed during melt-spun process.

Amorphization, Crystallization, and Magnetic Properties of Melt-Spun SmCo7−x(Cr3C2)x Alloys

Effects of Cr3C2 content and wheel surface speed on the amorphous formation ability and magnetic properties have been investigated for melt-spun SmCo7−x(Cr3C2)x (x=0.10-0.25) alloys. Ribbon melt-spun at lower wheel speed (30 m/s) has composite structure composed of mostly SmCo7, a small amount of Sm2Co17, and residual amorphous phases. The grain size of SmCo7 phase decreases with the increase of Cr3C2 content x. When melt spinning at 40 m/s, SmCo7−x(Cr3C2)x alloys can be obtained in the amorphous state for 0.15≤x≤0.25 with intrinsic coercive Hci of the order of 40–70 Oe. DSC analysis reveals that SmCo7 phase first precipitates from the amorphous matrix at 650∘C, followed by the crystallization of Sm2Co17 phase at 770∘C. Optimal coercivity Hci of 7.98 kOe and remanent magnetization Mr of 55.05 emu/g have been realized in SmCo6.8(Cr3C2)0.20 magnet subjected to melt spinning at 40 m/s and annealing at 650∘C for 5 min. The domain structure of the annealed ribbon is composed of interaction domains typically 100–400 nm in size, which indicates the presence of a strong exchange coupling between the grains.

Effect of processing parameter on hydrogen storage characteristics of as quenched Ti 45Zr 38Ni 17 quasicrystalline alloys

The present study deals with the microstructural changes with respect to the processing parameter (quenching rate) and their correlation with hydrogen storage characteristics of Ti 45Zr 38Ni 17 quasicrystalline alloys. The ribbons of the alloy have been synthesized at different quenching rates obtained through different wheel speeds (35, 40, 45 and 50 m/s) and investigated for their hydrogen storage characteristics. The lower cooling rate obtained through low wheel speed (35 m/s) produces, i-phase grains whose size ranges from 300-350 nm, whereas higher cooling rates obtained through high wheel speed (45 and 50 m/s) promote the formation of grains with size ranges from 100-150 nm in Ti 45Zr 38Ni 17 ribbons. It has been found that the ribbons synthesized at 35 m/s absorbed ∼2.0 wt%, whereas ribbons synthesized at 50 m/s absorbed ∼2.84 wt. % of hydrogen. Thus the hydrogen storage capacity of ribbon increases for the ribbons produced at higher quenching rate. One of the salient features of the present study is that the improvement of hydrogen storage capacity obtained through higher quenching rates (∼45 to 50 m/s wheel speed) leading to the formation of lower grain size.

Fabrication and Characterization of Melt-Extracted Co-Based Amorphous Wires

Amorphous Co68.15Fe4.35Si12.25B15.25 wires with smooth surface and circular cross section were fabricated by melt extraction technology using a copper wheel with a knife-edge cross section angle of 60 deg. The effect of some process parameters such as wheel circumference velocity, molten alloy feed rate, and temperature on the geometry and weight, i.e., melt extracted layer thickness, of wire was examined carefully. An optimum process parameter to produce high-quality circular wires was presented. A high resolution CCD video camera recorder was used to monitor the changing of the surface shape of molten alloy contacting the wheel tip under different conditions. It was found that the mechanism of the wire formation during the optimum process condition was controlled by the momentum mechanism, while in the low wheel speed region, heat transfer turned out to be a dominant factor. Some characteristics of the circular wires such as amorphous nature and tensile strength were also studied.

Microstructure of Rapidly Solidified CuFe10 Alloys

Rapid solidification of CuFe10 alloys was carried out by melt spinning at three wheel speeds 4, 12 and 36 m/s. The microstructure and solidification behavior of the ribbons was investigated by scanning electron microscopy (SEM). The results showed that the ribbons generally have a microstructure consisting of a fine dispersion of a Fe-rich phase in a Cu-rich matrix, and that the morphology and size of the Fe-rich phase vary with the wheel speed. For lower wheel speeds, the Fe-rich phase shows dual morphologies, dendrites and spheroids. The Fe-rich spheroids show a wide distribution of size, and have a larger mean size on the free surface than on the wheel surface. Some Fe-rich dendrites are distributed around the Fe-rich spheroids, this means liquid phase separation occurred during rapid solidification. The Fe-rich phase shows one morphology-spheroids and the size of Fe-rich spheroids decreasing as the wheel speed increasing. The results were discussed with respect to the formation of the Fe-rich spheroids during rapid solidification. The microhardness of the ribbons increasing with the increasing of the wheel speed for the grain refining and the increasing of supersaturated solid solution.

Microstructure and soft magnetic properties of Finemet-type ribbons obtained by twin-roller melt-spinning

Abstract Soft magnetic ribbons of Finemet-type (Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 ) alloys are synthesized by the twin-roller melt-spinning technique directly from the melt, at tangential wheel speeds of 15, 18, 19 and 20 m/s. The microstructure and the magnetic properties are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA), thermo-gravimetric analysis (TGA) and hysteresis loops measurements. Samples cooled at 20 m/s are amorphous, while those quenched at lower wheel speeds are partially crystalline. All samples studied present saturation magnetization values (150–160 A m 2 /kg) higher than the commercial Finemet alloys (∼135 A m 2 /kg), obtained by controlled crystallization of amorphous single-roller melt-spun alloys. Optimal soft magnetic properties – σ S =(154±8) A m 2 /kg and H C =(6.9±0.9) A/m – are found in samples quenched at 19 m/s, consisting of size-distributed bcc Fe–Si nanograins (∼18 nm in average) embedded in an amorphous residual matrix. A minority nanocrystalline magnetic phase (≤10 nm) is also detected.

Martensite and Nanocrystalline Phase Formation in Rapidly Solidified Ni<sub>2</sub>MnGa Alloy by Melt-Spinning

Microstructure of rapidly solidified Ni2MnGa ferromagnetic shape memory alloy has been investigated experimentally by melt-spinning technique. At a constant ribbon width of 3 mm, two speeds of melt spinning 17m/sec and 30m/sec at the extrema of conditions for a good quality of ribbon resulted in two thicknesses of the ribbon, viz., 62 μm and 44 μm, respectively. TEM and AFM analysis reveals the formation of very fine clusters of Ni2MnGa at lower wheel speeds. However at higher wheel speeds nanocrystalline Ni2MnGa particles of size about 10-20 nm and martensitic phases were confirmed.

Amorphous and nano crystalline phase formation in Ni2MnGa ferromagnetic shape memory alloy synthesized by melt spinning

Melt spinning technique was used to synthesize Ni2MnGa ferromagnetic shape memory alloy ribbons. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) analysis of the ribbon synthesized at lower wheel speed (20 m/s) reveal the formation of very fine clusters of austenitic phase of Ni2MnGa. However at higher wheel speed (30 m/s) the formation of martensite and nanoparticles of Ni2MnGa with a size range of 10–20 nm in the amorphous matrix is observed. Also an amorphous phase was observed at higher wheel speed in some areas of the ribbon. Annealing (1000 °C, 1 h) of the ribbon synthesized at higher wheel speed resulted in martensite and γ (gamma) phases. Amorphous phase, Ni2MnGa nanoparticles, and the martensite phase are analyzed in detail.

Effectiveness of Desiccant Coated Regenerative Wheels from Transient Response Characteristics and Flow Channel Properties—Part II: Predicting and Comparing the Latent Effectiveness of Dehumidifier and Energy Wheels Using Transient Data and Properties

In this paper, a new transient response theory is developed to predict the moisture or water transfer time constant and the fully developed flow moisture effectiveness of dehumidifier wheels and latent energy effectiveness of energy wheels. A new method to experimentally determine the latent energy or water transfer time constant is presented. This analytical model, which uses the new empirical time constant and its theoretical model, is then corrected for entrance length, carryover, sorption temperature changes, and manufacturing variations. The model permits the designer of these wheels and the HVAC applications engineer the opportunity to explore how each flow channel property and wheel operating condition changes the effectiveness. The theoretical latent and sensible effectiveness of energy wheels with molecular sieve and silica gel coatings are determined for two energy wheels, and these results are compared with the effectiveness calculated using experimental data at steady state ARI testing conditions. The comparisons are in agreement within the uncertainty bounds. The analytical model is also used to predict the latent effectiveness for two similar energy wheels where it is assumed that the desiccant coatings are interchanged. This comparison shows that the new hypothetical silica gel coating on the energy wheel would be more effective than the new molecular sieve coating on an energy wheel for the transfer of water vapor. The moisture transfer effectiveness is predicted for two dehumidifier wheels with the same design and desiccants as the tested energy wheels (i.e., the molecular sieve wheel and silica gel wheel). These wheels, which are used for supply air drying, are operated with the same ARI supply air condition and 5 rpm. Considering the comparisons for energy wheels, the molecular sieve and silica gel coatings are predicted to result in similar performance factors but with much lower effectiveness. This reduction in moisture effectiveness for the dehumidifier wheels is caused mostly by the reduction in wheel speed. Further research is required to investigate the performance of dehumidifier wheels at lower wheel speeds.

Synthesis, microstructure, and hard magnetic properties of melt-spun Nd3Fe27.5Ti1.5 and its nitride

Nd 3 Fe 27.5 Ti 1.5 alloy and its nitride were synthesized using melt-spinning, annealing, and nitriding route, and the effects of processing conditions on phase formation, microstructure, and magnetic properties were investigated. The following has been found: (1) Melt-spun Nd3Fe27.5Ti1.5 samples consist primarily of the 3:29 phase at low wheel speeds (5–10m∕s). The 1:7 phase was developed at higher wheel speed (20–25m∕s). Meanwhile, grain size is significantly reduced with increasing the wheel speed (from 33.5nm at 5m∕s down to 13.1nm at 25m∕s). As the wheel speed was increased to 40m∕s and above, the 1:7 phase disappears and an amorphous phase became dominant. (2) Annealing of the overquenched melt-spun samples transformed the amorphous phase into the 1:7 phase (when annealed at 600–700°C) or the 3:29 phase (when annealed at 800–900°C), and significant grain growth was observed when annealing temperature was at 800°C or above. (3) Nitriding at lower temperature (300–350°C) for longer time (24–45h) was preferred for introducing nitrogen atoms into the 1:7 or the 3:29 interstitial sites without destroying their crystalline structure. (4) The best magnetic properties obtained were Br=718mT, Hci=111kA∕m, and (BH)max=23kJ∕m3. This particular sample had the 1:7 phase with a grain size of ∼12nm and a nitrogen absorption of ∼4wt%.

Phase formation, microstructure and magnetic properties investigation in Cu and Fe substituted SmCo5 melt-spun ribbons

Abstract Magnetic properties and microstructure were investigated in Sm 17.24 Co 66.20 Cu 8.28 Fe 8.28 ribbons melt-spun at different wheel speeds of 5, 15, 30, 40 and 50 m/s. X-ray diffraction studies revealed that the ribbons melt-spun at lower wheel speed ( 7 , Sm 2 Co 7 and SmCo 5 , while higher wheel speed ribbons exhibited single phase SmCo 5 . The coercivity was found to increase with increase of the wheel speed. A high coercivity of ∼33 kOe was obtained in ribbon prepared at 50 m/s.

Creep feed grinding of a gamma titanium aluminide intermetallic alloy using SiC abrasives

Abstract Experimental results are detailed when creep feed grinding (CFG) a gamma titanium aluminide intermetallic alloy (γ-TiAl) Ti–45Al–8Nb–0.2C with SiC abrasives. When using low porosity wheels at a low wheel speed of 15 m/s and a material removal rate of 62.5 mm/s, G-ratios of ∼15 were produced with workpiece surfaces free of burn. At higher wheel speeds ≥25 m/s, cracks up to 1 mm deep were evident with extreme workpiece surface burn. By increasing the wheel porosity, specific power, cutting forces, workpiece surface burn and cracking were all reduced however, G-ratio was also reduced to ∼4 with heavy profile wear. Operation at 15 m/s with increasing feed rate and depth of cut reduced G-ratio still further to

Structure comparison between Th2Zn17-type and TbCu7-type Sm–Fe intermetallic compounds and their nitrides by means of 57Fe-Mössbauer spectroscopy

Samarium-iron intermetallic compounds were prepared by a melt spinning method with low and high wheel speeds, which resulted in a Th2Zn17-type and a TbCu7-type structure, respectively. Structure comparison between these types was investigated for Sm-Fe intermetallic compounds and their nitrides by 57Fe- Mossbauer spectroscopy.

Effect of Cu substitution on structure and magnetic properties of anisotropic SmCo ribbons

Anisotropic SmCo 7− x Cu x ( x=0–4.5) ribbons have been prepared by melt spinning at a low wheel speed of 5 m/s. Scanning electron microscopy results show that Cu-free and Cu-containing ribbons consist of equiaxed and columnar dendrite grains, respectively. The arrangement of columnar dendrite grains of the ribbons was found to be more ordered with increasing Cu content x. Together with the results of magnetic measurement, it is derived that Cu substitution is helpful to enhance the degree of preferred orientation of the c-axis of the columnar dendrite grains parallel to the longitudinal direction of the ribbons. In this way the rectangularity of demagnetization curves and the remanence ratio (defined as the ratio of remanent magnetization to saturation magnetization) of the samples are significantly improved. A remanence ratio of 0.90, which is close to that of sintered SmCo magnets, has been achieved in the ribbons with x=2.5. Because the domain-wall-energy gradient between the 1:5 and 2:17 phases, which determines the value of the coercive force arising from the domain wall pinning, may increase with x, the coercivity of the samples with x≤3.5 increases strongly with x. Without heat treatment, a coercive force ( i H c) of up to 9.2 kOe is obtained in the ribbons with x=3.5.

Influence of Fe, Zr, and Cu on the microstructure and crystallographic texture of melt-spun 2:17 Sm–Co ribbons

A comprehensive study on melt-spun 2:17 Sm–Co ribbons prepared at low wheel speed was undertaken in order to understand the effects of composition on the microstructure and formation of crystallographic texture. A high degree of texture was observed in melt-spun SmCo8.5 and Sm(Co0.9Fe0.1)8.5 ribbons prepared at 5 m/s with easy magnetization axis being parallel to the longitudinal direction of the ribbons. However, Zr was found to reduce the crystallographic texture and the Sm(Co0.74Fe0.1Zr0.04Cu0.12)z ribbon is isotropic. Scanning electron microscopy (SEM) observation showed that the formation of texture is attributed to a regular dendritic structure, with their long axis parallel to the longitudinal direction of the ribbons. The size and alignment of dendritic grains are significantly modified by Zr and Cu substitution for Co and the Sm(Co0.74Fe0.1Zr0.04Cu0.12)z ribbons are composed of many small areas with different alignments of the dendrites. X-ray diffraction patterns of crushed isotropic (d⩽20 μm) ribbons of Sm(Co0.74Fe0.1Zr0.04Cu0.12)8.5 show very high degree of texture and thus these ribbons have potential applications in preparing anisotropic bonded magnets. After an appropriate annealing, a coercivity of over 2.5 T has been obtained in Sm(Co0.74Fe0.1Cu0.12Zr0.04)z ribbons with z=7.5 and 8.0, and the coercivity mechanism is typical of the domain-wall pinning. This is consistent with transmission electron microscopy observation, which reveals a cellular and lamellar structure in the as-annealed ribbons.

Magnetic Anisotropy of Sm(Co0.68Fe0.22Cu0.08Zr0.02)7.7 Ribbons Produced by Melt Spinning

A high degree of texture was observed in melt-spun Sm(Co0.68Fe0.22Cu0.08Zr0.02)7.7 ribbons prepared by single-roller melt spinning at low wheel speed; their easy magnetization axis was parallel to the ribbon plane. Magnetization studies showed an obvious magnetic anisotropy and a 90% higher remanance in ribbons for the field parallel to the longitudinal direction (8.5 kGs) than that for the field parallel to the wide direction (4.4 kGs); this was attributed to a dendritic structure of needle-size grains (2–3 × 10–40 μm) with their long axis parallel to the ribbon plane. This texture allowed the development of a new process for producing anisotropic permanent magnets. The domain structure was studied by magnetic-force microscope. A highly ordered and strip-shaped magnetic domain structure was observed on the surface of the ribbons. This was due to the preference for tetragonal c-axis orientation parallel to the surface of melt-spun ribbons. We calculated the domain wall energy γ and critical single-domain particle size Dc of Sm(Co0.68Fe0.22Cu0.08Zr0.02)7.7 ribbons.

Exchange coupled Nd2Fe14B/α-Fe nanocomposite magnets with fine α-Fe grains obtained by low wheel speed spinning

Exchange coupled Nd2Fe14B/α-Fe nanocomposite magnets have been synthesized by melt-spinning. The effect of wheel speed on the magnetic properties and microstructure has been studied. The results show that a uniform Nd2Fe14B/α-Fe nanocomposite structure with fine α-Fe grains can be developed at an optimum wheel speed of about 12 m/s. After a low temperature annealing, the magnetic properties can reach maximum values: iHc=432.2 kA/m, Jr=1.08 T, (BH)max=115 kJ/m3. With further increasing the wheel speed, the volume fraction of an amorphous phase increases. The microstructure of the ribbons becomes nonuniform after a subsequent high temperature crystallization, and several α-Fe grains abnormally grow to about 100 nm, deteriorating the magnetic properties of the ribbons.

Microstructures and modification performance of melt-spun Al-10 Sr alloy

The microstructures of Al-10 Sr alloy quenched at various wheel speeds have been investigated using X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The experimental results show that the microstructures of melt-spun Al-10 Sr alloy are quite different from those of ingot-like alloy consisting of coarse plate-like Al4Sr embedded in the eutectic matrix. For lower wheel speeds of 500 and 1000 rpm, the microstructure is composed of nanoscale particle-like Al4Sr embedded in α-Al solid solution. With wheel speeds exceeding 1500 rpm, the formation of primary Al4Sr phase is completely suppressed and the eutectic microstructure consisting of alternate dark and bright zones is obtained. Eutectic Al4Sr in dark zones is stripe-like and irregular blocky, while regular stripe-like in bright zones, about 10–20 nm in width. Furthermore, modification tests indicate that the modification performance of melt-spun Al-10 Sr alloy is much better than that of ingot-like alloy, reducing the amount of Sr addition and greatly shortening the incubation time. The reasons for the formation of microstructures and the improvement of modification performance of melt-spun Al-10 Sr master alloy have also been discussed.

Crystallographic texture and magnetic anisotropy of α-Fe/Nd2Fe14B nanocomposites prepared by controlled melt spinning

In this study, α-Fe/Nd2Fe14B nanocomposite magnets with strong crystallographic texture were prepared by controlled melt spinning. For a relatively low wheel speed of 10 m/s, the c-axis texture of the Nd2Fe14B crystals is predominantly perpendicular to the plane of the ribbon, but it switches to parallel to the ribbon plane direction at a higher wheel speed of 20 m/s. The magnets show strong magnetic anisotropy between in and out of the ribbon planes. High remanence of 0.74Ms and a large energy product of 24.3 MGOe were observed parallel to the ribbon plane direction in the magnets prepared at a wheel speed of 20 m/s.

Effect of the substitution of Gd for Sm on magnetic anisotropy ofmelt-spun Sm1-xGdxCo5 ribbons

Magnetically anisotropic Sm1-xGdxCo5 (0⩽x⩽0.5) ribbons have been prepared by single-roller melt spinning at a lowwheel speed of 5 m s-1. X-ray diffraction results show that thesubstitution of Gd for Sm enhances the relative intensity of thediffraction peak of index (200) and favours the formation of a strong(002) texture parallel to the longitudinal direction of the ribbons. Thisresults in the increase of the remanence ratio with the increase of x.By scanning electron microscopy measurements, it is found that theGd-containing ribbons have a more regular grain arrangement and a morehomogeneous distribution of grain size compared to the Gd-free ribbons.The rectangularity of demagnetization curves is obviously improved withthe increase of x. A maximum remanence ratio (0.93) and bestrectangularity of the demagnetization curves have been obtained forribbons with x = 0.5. However, the replacement of Sm by Gd also leads tothe linear decrease of the remanence of SmCo5 ribbons. The optimummagnetic properties, Mr = 0.84 T, iHc = 10.4 kOe,(BH)max = 16.7 MGOe, have been achieved in the as-annealed ribbonswith x = 0.2.