Wheel-side Surface Research Articles

Direct synthesis of Fe-Si-B-C Cu nanocrystalline alloys with superior soft magnetic properties and ductile by melt-spinning

Structure, magnetic properties and ductile of melt-spun Fe83-xSi4B13-yCyCux (x = 0–1.7; y = 0–8) alloys were investigated. The addition of 1.7 at.% Cu in a Fe83Si4B13 amorphous alloy generates abundant α-Fe crystals by providing nucleation sites, and further C doping promotes the growth of the crystals by suitable turning amorphous-forming ability, hence they increase saturation magnetic flux density (Bs) and slightly worse magnetic softness of the as-spun alloys. The as-spun Fe81.3Si4B7C6Cu1.7 alloy possesses a combined structure of a fully amorphous layer in wheel side surface and predominating nanocrystalline structure with gradually enlarged α-Fe crystal, whose average size and volume fraction are determined as about 12 nm and 32%, respectively, therefore superior soft magnetic properties and ductile with a high Bs of 1.74 T, coercivity (Hc) of 32.7 A/m, effective permeability (μe, at 1 kHz) of 3200 and high relatively strain at fracture (εf) of 3.61% can be achieved directly in this alloy by only using melt-spinning. The annealing at 578 K releases internal stress, promotes the growth of the α-Fe crystals and remains the amorphous layer of the Fe81.3Si4B7C6Cu1.7 alloy, then improves the soft magnetic properties and maintains the superior ductile with increasing the Bs and μe to 1.80 T and 14,100, respectively, lowering the Hc to 9.4 A/m and slightly reducing the εf to 2.39%. The combination of superior soft magnetic properties and ductile and simplified synthesis process entitles the Fe-Si-B-CCu nanocrystalline alloys great potentials in high performance electromagnetic applications.

Surface oxidation and crystallization of FeNi-Based soft magnetic nanocrystalline and amorphous nanocomposite alloys

In this work, we present characterization of surface oxidation and crystallization behavior of Metal Amorphous Nanocomposite (MANC) (Fe 70 Ni 30 ) 80 Nb 4 Si 2 B 14 alloys via complementary x-ray diffraction, electron microscopy, and x-ray photoelectron spectroscopy techniques. An adherent amorphous oxide of roughly 15–20 nm in thickness is observed on the wheel side of the ribbon, enriched in Fe relative to Ni and with significant content of Si and Nb as would be expected based upon a comparison of the Gibbs free energy of formation of the stable oxide phases. The amorphous character of the oxide is likely to result from the significant Si-content coupled with the amorphous and nanocrystalline character of the underlying metallic layer. Higher density of FeNi-enriched nanocrystals is also observed within ∼100 nm of the wheel-side surface, presumably due to reduction in local glass former concentration. A rough, crystalline copper oxide layer is also present and forms through contact between the copper wheel and the solidifying melt during the rapid solidification process. On the air side of the ribbon, a crystalline oxide layer of ∼15–20 nm is formed as well as intergranular oxidation that penetrates along the grain boundaries between highly textured surface crystallites of ∼50–100 nm in size. The crystalline nature of the oxide on these surfaces is asserted to result from the lack of significant Si-content and the pre-existing surface crystallites that form during the rapid solidification process which promote a crystalline oxide surface layer. These results shed new insights into the details of surface oxidation and can help to inform processing and alloy composition adjustments which seek to tailor surface properties.

Effect of CO gas on surface profile and magnetic properties of Fe–Si–B amorphous ribbons

The Fe–Si–B amorphous ribbons with various CO ventilation amount were prepared by planar-flow melt spinning method. The effect of CO gas on surface quality, magnetic properties and core loss of amorphous ribbons were investigated. With the increasing CO ventilation, the wheel side surface roughness, average air pocket size and air pocket quality decrease, the ribbon grows thicker, but air side surface roughness remains almost no changes. The three samples have reached to a fully amorphous structure. Meanwhile the diffraction angle corresponding the maximum intensity of each broad diffraction peak decrease slightly with increasing CO ventilation. There is no significant differences in the onset temperate of second exothermic peak (Tx2) and the crystallization peak temperature (Tp1 and Tp2) among the amorphous ribbons prepared with various CO ventilation, but the onset temperate of first exothermic peak (Tx1) increases slightly with the increasing CO ventilation. The room temperature hysteresis loops of amorphous ribbons show that surface quality have significant effect on magnetic properties. The coercivity (Hc), core loss (P1.35/50), magnetic polarization (B80) and permeability (µ) among the ribbons are improved with better surface quality, though the saturation magnetic flux density almost keeps same. Core loss are separated by the scaling theory, and experiment dates show a good agreement with the predicted data. Thus the scaling theory is suitable for Fe–Si–B amorphous alloys. The surface quality has more significant effect on hysteresis losses than eddy current loss at low frequency.

Modeling of integral cutting tool grooves using envelope theory and numerical methods

A groove is a key component of the structure of end mills, drills, and other integrated cutting tools. Machining a groove is one of the most difficult, time-consuming, and costly manufacturing process; therefore, for the sake of reduction of the machining cost and meeting the environmental regulations, the modeling of a machined groove with known wheel geometry and position is necessary for cutting tool manufacture. In order to reveal the process more clear and precise, the envelope theory and numerical methods are used. First, the basic calculation procedure for groove section points is built using a meshing equation. Accordingly, four universal problems for the simulation of groove manufacturing process are analyzed by four typical examples. Namely, the wheel side surface may interfere the machined tool edge and lead to an incorrect simulation; the wheel revolution surface may overcut the machined tool edge and produce fake points that would disturb the results; the tip point might not be precise enough; and the groove section points might be distributed unevenly and result in an imprecise groove section. The conditions to solve these problems are established by mathematical formulas and calculated by numerical methods. In addition, an integral procedure is built to simulate the machined groove with correct, precise, and even distribution points. Finally, groove simulation software is developed using MATLAB GUI, and the results are verified.

Formation mechanisms of NaZn13-type phase in giant magnetocaloric La–Fe–Si compounds during rapid solidification and annealing

The promise of the La–Fe–Si alloys for energy efficient magnetic refrigeration devices stems from a strong magneto-structural transition in the La(Fe,Si)13 (1:13) phase near room temperature. The formation of the 1:13 phase during rapid solidification was compared in detailed microstructural studies of the wheel-side and free-side surfaces of melt-spun ribbons. On the free-side, clusters of similarly-oriented crystallites are observed; chemical segregation of La, Fe, and Si leads to a nanoscale texturing of α-Fe and LaFeSi. In contrast, equiaxed 1:13 grains ∼100–400 nm form the microstructure of the wheel-side surface, with a minor α-Fe phase precipitated in the matrix. Upon annealing, the 1:13 phase grows via dissolution of the α-Fe phase on the wheel side and a peritectoid reaction from the free side. For longer annealing times, the completion of the peritectoid reaction improves the magnetic entropy change under a magnetic field change of 1.5 T from 12 J/kg K (2 min) to 17 J/kg K (2 h), and increases the Curie temperature of the ribbons from 189 K to 201 K.

Surface oxidation of the Fe based amorphous ribbon annealed at temperatures below the glass transition temperature

The Fe based amorphous ribbons with the nominal compositions Fe84.2−xC11.0SixB3.9P0.9 (x=4.5 and 13.5 at.%) were oxidized at low temperatures of 300 and 400°C (i.e., well below the crystallization temperature) for 24h in the air atmosphere. Significantly different oxidation kinetics between surfaces of the wheel side and the air side were observed, respectively. A continuous amorphous Si oxide layer with a few nanometers in thickness was formed on the air side surface of as-spun ribbon and effectively protected the ribbon from oxidation during annealing. However, discontinuity of the amorphous Si oxide layer was observed near casting defects on the wheel side surface. Moreover, due to low cooling rate near the casting defect regions, nanocrystals can be formed resulting in enhanced oxidation kinetics of the wheel side surface. As the annealing temperature is increased to 400°C, the air side surface exhibited deteriorated oxidation resistance attributed to partial nanocrystallization of α-Fe. Nanocrystals of α-Fe formed on the surface acted as effective nucleation sites for the formation of iron oxides. Increasing annealing temperature leads to the increased thickness of both amorphous and crystalline oxide layers. However, effects of surface casting defects on the oxidation resistance can be significantly reduced by increasing the Si content.

Model of temperature field for the preparation process of melt-spun NdFeB powders

Melt-spun ribbons which are the important raw material for hot-deformed magnets can be prepared by single-roller melt-spinning. In order to prepare well-structured ribbons, the model of temperature field for single-roller melt-spinning process was constructed in this work. The heat conduction in this process was simplified as one dimensional heat conduction problem. It was shown by modeling that, the temperature field in the melt-spinning before solidification in this model could be described as this equation T(x,t)=Tmoexp[−k(x−x0)−k2αt]+T0. The temperature T(x,t) of the alloy melts decreased with increased position x and cooling time t exponentially from the wheel-free surface to the wheel-side surface. The constant k determined the decrease speed of alloy temperature T(x,t), which was proportional to the interfacial heat transfer coefficient h and the interfacial area of heat conduction A0, but inversely proportional to the thermal conductivity K. x0 was the thickness of the alloy melt. With increased x0, the temperature difference between wheel-free surface and the wheel-side surface became larger, which would lead to larger difference in grain size. In experiments, the influence of melt-spinning process parameters on the temperature field model was discussed, such as cooling roller materials, wheel speed, and so on. Melt-spun ribbons prepared by single-roller melt spinning at different wheel speed were investigated and magnetic properties of die-upset magnets from melt-spun ribbons on different cooling roller were analyzed. The variation of grain size in the depth direction consisted with temperature field model. This model provided directions for the preparation of melt-spun ribbons with uniformly distributed fine grains, which were very necessary for producing hot-deformed magnets with high magnetic performance.

Enhanced giant magnetoimpedance effect and field sensitivity in Co-coated soft ferromagnetic amorphous ribbons

A 50 nm-thick Co film has been grown either on the free surface (surface roughness, ∼6 nm) or on the wheel-side surface (surface roughness, ∼147 nm) of Co84.55Fe4.45Zr7B4 amorphous ribbons. A comparative study of the giant magnetoimpedance (GMI) effect and its field sensitivity (η) in the uncoated and Co-coated ribbons is presented. We show that the presence of the Co coating layer enhances both the GMI ratio and η in the Co-coated ribbons. Larger values for GMI ratio and η are achieved in the sample with Co coated on the free ribbon surface. The enhancement of the GMI effect in the Co-coated ribbons originates mainly from the reduction in stray fields due to surface irregularities and the enhanced magnetic flux paths closure. These findings provide good guidance for tailoring GMI in surface-modified soft ferromagnetic ribbons for use in highly sensitive magnetic sensors.

Differences of element distribution between free and wheel side surface of NdFeB/α-Fe ribbons

The ribbons of NdFeB/α-Fe composite alloy were prepared by melt spinning and post crystallizing technique. The element distributions and phase component of both surfaces of as-spun ribbons were measured by energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). Because of the centrifugation, a segregation of B, Fe, and Nd concentrations was observed at the cross section. After crystallizing annealing, the element concentration segregation still existed in the as-crystallized ribbons. Due to the segregation of B, Fe, and Nd, the B-rich phase was observed near the wheel side surface. The B-rich phase may deteriorate the magnetic property of NdFeB/α-Fe composite alloy.

Evolution of crystallographic alignment in Tb-Fe-B melt-spun ribbons

Ternary Tb-Fe-B ribbons were prepared via melt-spun technique under different wheel speeds of 5-25 m/s. Effect of wheel speed on the crystal structure and microstructure of the ribbons was investigated. All the ribbons quenched under different wheel speeds crystallized in single Tb 2Fe 14B phase with tetragon structure. Different crystallographic alignment evolutions were observed in the free side surface and wheel side surface of the ribbons. On the free-side surface, an in-plane c-axis crystal texture of Tb 2Fe 14B phase was found in the ribbons quenched at 5 m/s. However, with the increase in the wheel speed, the direction of the c-axis texture turns to perpendicular to the ribbon surface. On the wheel-side surface, a strong c-axis texture perpendicular to the ribbon surface was observed in the ribbons quenched at 5 m/s, and then weakened gradually with the increase in the wheel speed. Further investigation showed that the competition of the two types of temperature gradients during the quench process was responsible for the crystallographic alignment evolution in the ribbons.

Effect of Structural Defects, Surface Irregularities, and Quenched-In Defects on Corrosion of Zr-Based Metallic Glasses

X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) revealed a fully amorphous structure for as-cast bulk metallic glass (BMG) and melt-spun ribbons of Zr 52 Ti 6 Al 10 Cu 18 Ni 14 prepared by copper mold casting and the melt-spinning technique, respectively. For melt-spun ribbons, the wheel-side surface contained a higher concentration of quenched-in defects (air pockets), whereas surface irregularities were noticed in the air side. Fluctuation microscopy indicated more medium-range order for the as-cast structure of BMG than for the melt-spun ribbon, whereas in the BMG, the medium-range order was located more in the central region than in the periphery. Macro- and microcell electrochemical experiments of the BMG along the cross section and macrocell experiments of each side of the ribbons in dilute acidic chloride environments indicated that the corrosion resistance of the BMG decreased with the increase in the medium-range order; the medium-range order, however, was less deleterious than either the surface irregularities or the quenched-in defects from the viewpoint of corrosion. A surface film formed on the metallic glasses in a dilute acidic chloride environment mainly consisted of oxide of zirconium, in which zirconium was present in the Zr +3 , Zr +2 , and Zr +1 state in the BMG and in the air-side and wheel-side surfaces, respectively.

Effect of surface morphology on atmospheric corrosion behaviour of Fe-based metallic glass, Fe67Co18Si14B1

The nature of atmospheric corrosion behaviour of an as-cast metallic glass, Fe67Co18Si1B14 ribbon, was evaluated. The wheel side surface of the ribbon was more corroded than the air side surface, due to the higher density of air pockets present. The phases present in atmospheric rust were analysed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) to be goethite, lepidocrocite, magnetite, cobalt oxide and cobalt hydroxide phases. Goethite and lepidocrocite were in amorphous form. The nature of rusting was understood by scanning electron microscopy (SEM). Nucleation of rust started at preferred locations on the surface and grew along the surface in certain directions.

The role of melt pool behavior in free-jet melt spinning

The influence of melt pool behavior on the competition between the nucleation of crystalline solidification products and glass formation is examined for an Fe-Si-B alloy. High-speed imaging of the melt pool, analysis of ribbon microstructure, and measurement of ribbon geometry and surface character all indicate upper and lower limits for melt spinning (MS) rates for which fully amorphous ribbons can be achieved. Comparison of the relevant time scales reveals that surface-controlled melt pool oscillation may be the dominant factor governing the onset of unsteady thermal conditions accompanied by varying amounts of crystalline nucleation observed near the lower limit. At high rates, the influence of these oscillations is minimal due to very short melt pool residence times. However, microstructural evidence suggests that the entrapment of gas pockets at the wheel-metal interface may play a critical role in establishing the upper rate limit. An observed transition in wheel-side surface character with an increasing MS rate supports this contention.

Magnetic properties and Mössbauer effect study of Nd 60Fe 30Al 10 ribbons

The magnetic properties of Nd 60Fe 30Al 10 ribbons were studied in the as-cast state as well as after annealing. The anomaly observed in the temperature dependence of the ac-susceptibility depends on frequency and the superposed dc-field and disappears when the wheel-side surface of the ribbon up to a thickness of 9 μm is removed. On the contrary, the 57 Fe Mössbauer spectra show always two peaks in the hyperfine field distribution which are correlated to high and low magnetic moments, independent of the heat- and surface treatments. The intrinsic coercivity shows a strong time dependence for the whole temperatures range.

Microstructural evolution in rapidly solidified Al-Cu-Si ternary alloys

Several Al-Cu-Si alloys were melt spun to produce stable, fine scale microstructures suitable for superplastic deformation and consolidation. Scanning electron microscopy of the ribbon cross-sections reveal two distinct alternating microstructural morphologies, suggesting transitions in solidification behavior. One structure consists of intimately interlocked α-Al and θ (Al2Cu) phases with dispersed spheroids of (Si). The other structure consists of equiaxed or cellular-dendritic α-Al with interdendritic θ and (Si). The latter was found in the middle portion of the ribbon cross-section when cast at a low speed, and throughout the ribbon cross-section when cast at high speed. The dendritic structure appears to result from independent nucleation events in the undercooled liquid ahead of the solid-liquid interface. The solidification mechanism for the interlocked structure appears to involve multiple nucleation of the θ phase followed by its cooperative growth with the α-Al phase. This cooperative growth is unlike that which forms a lamellar structure, as it results in a branched, randomly oriented network. We postulate that the (Si) phase is the first phase to form from the undercooled liquid, and it is uniformly dispersed throughout the undercooled melt. The (Si) spheroids provide nucleation sites for the θ phase because of its observed association with the θ phase. The α-Al grain size varies from 1 μm near the wheel side surface of the ribbon to 8 μm with sub-grains near the free surface. The size of the θ and (Si) phases is on the order of a μm and less. The microstructural size scale appears to be small enough for this material to exhibit superplastic behavior when deformed.

Effects of composition on microstructures of rapidly solidified Ni–Al alloys

Microstructures of melt-spun Ni–Al alloys with compositions from 61–85 at% Ni were studied by means of transmission electron microscopy, X-ray diffraction analysis and optical microscopy. The microstructures of as-quenched ribbons exposed to cooling rates of the order of 106 K s-1 reflect the transition from primary β-NiAl to γ-Ni solidification with increasing nickel content. In 70 at% Ni alloy ribbons, martensitic NiAl grains were detected near the wheel-side surface contrasting with anomalous and lamellar eutectic microstructure in the top part. Directly ordered Ni3Al grains with single (or large) antiphase domains (APDs) and a minor eutectic fraction were observed in 75 at% Ni alloy ribbons. Samples containing 80 at% Ni exhibit mainly single-phase Ni3Al grains with 10–20 nm sized APDs indicating sequential ordering. Weak L12 ordering was even detected in 85 at% Ni ribbons which displayed ordered antiphase zones of 1 nm size. Disordered γ-(Ni) films on grain boundaries can be discounted for 80 at% Ni ribbons, but occurred near the top of 85 at% Ni samples. The results are explained in terms of the reassessed Ni–Al phase diagram employing recent corrections near to the Ni3Al composition and new results on phase formation in undercooled Ni–Al melts. © 1998 Kluwer Academic Publishers

Effects of Zr on microstructure and mechanical properties of Al-Cu base ribbons spun by planar flow casting

The effects of the Zr addition on the solidification behavior and mechanical properties of the AI-Cu alloy ribbon have been investigated. Zr addition reduced the average grain size of the ribbon at the wheel-side surface, and promoted the microstructural transition into cellular/dendritic structure. Another noteworthy effect of Zr was the homogenization of the microstructure. The addition of Zr up to 0.5 wt.% in the /U-4.3 wt.% Cu ribbon resulted in a considerable increase in hardness at both the wheel-side and the air-side surfaces. The yield strength increased with the addition of Zr due to the grain refincment and more homogeneous distribution of ZrAI, particles. despite no noticeable improvement of the ductility.

Corrosion behaviour of rapidly solidified Zr 76Ni 16Fe 8 alloy in chloride environments

Amorphous alloys possess better corrosion resistance than crystalline alloys because these are devoid of defects present in a crystalline lattice and are compositionally more homogeneous. The conclusions drawn by the authors are as follows: (1) Corrosion behavior of rapidly solidified Zr[sub 76]Ni[sub 16]Fe[sub 8] alloy ribbon varies across its thickness in chloride environments. (2) Wheel side surface of the ribbon (fully amorphous structure) possesses better corrosion resistance than the air side surface of the ribbon (partial crystallinity) in the chloride environments. (3) Among the three factors, namely, partial crystallinity, air pockets and compositional difference induced in rapidly solidified Zr[sub 76]Ni[sub 16]Fe[sub 8] alloy ribbon, partial crystallinity appears to be the most harmful as far its corrosion resistance in chloride environments is concerned.

Surface crystallization in melt-spun metallic glasses

A series of hypoeutectic FeSiB metallic glasses produced by single-roller melt spinning were found to have substantial wheel-side surface crystallization. These crystals were shown to be associated with areas on the ribbon surface which were in good contact with the wheel rather than in the depressions formed by gas entrainment during casting, as has been previously suggested for similar effects in other alloys. Transmission electron microscopy revealed that the crystals have a fine cellular substructure with the intercellular spaces freezing as glass and that the structure becomes progressively finer during growth.

Amorphous ribbon formatin and the effects of casting velocity

Experimental relations between melt puddle length and ribbon thickness in the steady state spin casting of Fe 81.5B 14.5Si 4 amorphous ribbons are analyzed with a continoues casting model to estimated the ribbon formation temperature T t and the metal-wheel interfacial conductance h. The result T t ≈ 1000 ° C indicates that a high viscosity liquid layer contributes to the final ribbon thickness about as much as the amorphous solid layer defined by the isotherm T g = 450 ° C. It is also shown that T t remains constant but that h increases from 12 to 50 cal cm −2 s −1 K −1 with increasing wheel speed. The improved h value at higher casting speeds results from better melt-wheel contact as revealed in the contact pattern on the wheel-side surface of the ribbons.