Structure and magnetocaloric effect in melt-spun La(Fe,Si)_(13) and MnFePGe compounds

The magnetocaloric properties of melt-spun La(Fe,Si)13 and MnFePGe compounds were investigated. Very large value of magnetic entropy change ｜ΔS｜=31 and 35.4 J·(kg·K)-1 under 5 T were obtained at 201 K in LaFe11.8Si1.2 melt-spun ribbons and at around 317 K in Mn1.1Fe0.9P0.76Ge0.24 melt-spun ribbons, respectively. The large magnetocaloric effect results from a more homogenous element distribution related to the very high cooling rate during melt-spinning. The excellent MCE properties, the low materials cost and the accelerated aging regime make the melt-spun-type La(Fe,Si)13 and MnFePGe materials an excellent candidate for magnetic refrigerant applications.

Crystallization behaviour and high coercivity of (Nd,Pr)_(13)Fe_(80)Nb_1B_6 melt-spun ribbons

Amorphous （Nd,Pr）13Fe80Nb1B6 ribbons were crystallized at 670-730°C for 5-25 min to study the effects of isothermal crystallization on their behavior and magnetic properties. XRD results indicate that the isothermal incubation time is 12, 5, and less than 5 min at 670, 700, and 730°C, respectively. High coercivities, with the maximum value of iHc = 1616 kA/m at 700°C for 19 min, measured by a physical property measurement system, are obtained in the crystallized ribbons. This is mainly attributed to the addition of Pr and Nb, because Pr2Fe14B has a higher anisotropic field than Nd2Fe14B, and Nb enriched in the grain boundary regions can not only reduce the exchange-coupling effects among hard grains, but also impede grain growth during the crystallization process. In addition, it should also be related to the characteristics of the furnace that the authors designed.

Microstructure and magnetocaloric properties in melt-spun and high-pressure hydrogenated La_(0.5)Pr_(0.5)Fe_(11.4)Si_(1.6) ribbons

The effects of wheel speeds and high-pressure hydrogen treatment on phase evolution,microstructure,and magnetocaloric properties in La_(0.5)Pr_(0.5)Fe_(11.4)Si_(1.6)melt-spun ribbons are studied in this work.The results reveal that the increase of wheel speed is beneficial to the formation of cubic NaZn_(13)-type phase and the grain refinement.The optimized wheel speed for microstructural and magnetocaloric properties is 30 m/s.The largest entropy change of 18.1 J/kg·K at 190 K under a magnetic field change of 0 T-5 T is obtained in La_(0.5)Pr_(0.5)Fe_(11.4)Si_(1.6)ribbons melt-spun at 30 m/s.After a high-pressure hydrogen treatment of 50 MPa,the Curie temperature of the ribbons prepared at 30 m/s is adjusted to about 314 K and the large-ΔS_(M)of 17.9 J/kg·K under a magnetic field change of 0 T-5 T is achieved at room temperature with almost none hysteresis loss.The small thermal and magnetic hysteresis and the large-ΔS_(M)make the La_(0.5)Pr_(0.5)Fe_(11.4)Si_(1.6)hydride ribbons appropriate for magnetic refrigerant applications around room temperature.

Microwave Behavior of α-Fe/Fe_3B/Y_2O_3 Nanocomposites in GHz Range Prepared by Melt-Spun Technique

Nanocomposites α-Fe/Fe 3B/Y 2O 3 were prepared by a melt-spun technique, and the electromagnetic wave absorption properties were measured in the 0 05～20 05 GHz range. Compared with α-Fe/Y 2O 3 composites, the resonance frequency (f r) of α-Fe/Fe 3B/Y 2O 3 shifted to a higher frequency range due to the large anisotropy field (H A) of tetragonal Fe 3B (～0 4 mA·m -1). The relative permittivity (ε r=ε r′-jε r″) was constantly low over the 0 5～10 GHz region, which indicates that the composite powders have a high resistivity (ρ=～100 Ωm). The effective electromagnetic wave absorption (RL<-20 dB) was obtained in a frequency range of 2.7～6.5 GHz on resin composites of 80% (mass fraction) α-Fe/Fe 3B/Y 2O 3 powders, with thickness of 6～3 mm respectively. A minimum reflection loss of -33 dB was observed at 4.5 GHz with an absorber thickness of 4 mm.

Effects of Stretching Ratio and Temperature on Phase Transition of Melt-spun Poly(Vinylidene Fluoride) Fibers

The effects of stretching ratio and stretching temperature on pbase transition of melt-spun poly （ vinylidene fluoride ） fibers were investigated and analyzed by using scanning electron microscopy, wide angle X- ray diffraction, differential scanning calorimetry and Fourier transfer infrared spectroscopy. The β phase exists in the as-spun fiber. The β phase content increases as the stretching ratio increases. When the stretching temperature is lower than 100 ℃ , enhancing temperature is good for the transition of phase a to ft. By contrast, when the stretching temperature is higher than 100 ℃ , enhancing temperature is unfavourable for the transition of phase a to β. Increasing the draw temperature increases the α-phase content.

The effect of heat treatment on microstructure of the melt-spun Mg-7Y-4Gd-5Zn-0.4Zr alloy

The microstructure evolution of the melt-spun Mg–7Y–4Gd–5Zn–0.4Zr alloy during annealing treatment has been investigated by using X-ray diffraction(XRD),optical microscope(OM),differential scanning calorimetry(DSC)and transmission electron microscope(TEM).The results indicated that two kinds of primary grains were contained in the melt-spun alloy.One was the supersaturated magnesium matrix,and the other was the 18R-LPSO phase.The 18R-LPSO phase transformed into the 14H-LPSO phase during annealing treatment at 300 ℃ for 0.5 h.The new precipitate of the 14H-LPSO phase was found at 300 ℃ for 5 h.Lots of linear precipitates formed as well as some precipitate with quadrangular morphology in matrix at 500 ℃ for 0.5 h.The melt-spun alloy displayed the highest hardness of 103 NHV after annealing treatment at 300 ℃ for 5 h.

Formation of Omega-like Nanocrystalline in the Melt-Spun Nd_(85)Al_(15) Alloy by Phase Transformation

Microstructure and subsequent phase transformations on heating of the melt-spun Nd85Al15 alloy have been studied by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. The melt-spun Nd85Al15 alloy shows two-stage transformation processes as follows: amorphous+72 nm supersaturated bcc-Nd(AI) solid solution-7 nm omega-like phase-AINd3+hexagonal Nd. The activation energies for the first and second transformation were found to be 100 kj/mol and 188 kj/mol, respectively. The formation mechanism of nanoscale omega-like phase is discussed.

The Structure and Magnetic Properties of Co₇₇Zr₁₈W₅Melt-Spun Ribbons

Based on X-ray diffraction, microscopic and magnetic analysis, the structure and magnetic properties of Co77Zr18W5 melt-spun ribbons were studied in this paper. A new element to stabilize the metastable Co5Zr phase was found and the coercivity observed in Co-Zr alloys can be obviously enhanced by proper tungsten substitution. The Curie temperature of Co77Zr18W5 ribbons is 475℃ which suggests that W doped Co-Zr alloys may become an attractive candidate perma- nent magnets for practical applications in high temperature. Annealing of the Co77Zr18W5 ribbons results in a decrease of the coercivity which confirmed that the hard magnetic phase is Co5Zr phase in 77Zr18W5 melt-spun ribbons.

Effects of Cobalt Content and Preparation on Electrochemical Capacity of AB_5-Type Hydrogen Storage Alloys at Different Temperature

The effects of Co as a substituent for Ni on microstructure and electrochemical capacity of hydrogen storage alloys MI（NiCoMnAl）5.4 at -30- ＋80 ℃, in which the content of Co was 0, 1.31%, 2.63%, 3.94%, 5.25%, and 6.56% （mass fraction）, respectively, were reported. All of the alloys were prepared by vacuum induction melting followed by melt-spinning. It is found that the electrochemical capacity of alloys at different temperature depends upon the compositions and preparation methods. The electrochemical capacity of alloys increases at higher temperature （40 - 80 ℃ ） and decreases at lower temperature （ - 30 - 0 ℃ ） with an increasing cobalt content. With an increasing temperature, melt-spinning is more favorable for improved capacity of the alloys than casting. Analyses of the charging/discharging potential curves illustrate that higher cobalt content and melt-spinning techniques are more effective to increase the capacity at higher temperature because of the higher hydrogen evolution potential. On the contrary, the capacity of alloys at lower temperature can be increased by decreasing cobalt content and casting, which is ascribed to higher hydrogen evolution potential and delayed hydrogen evolution reaction, as well as reduced potential drop in the charging/discharging process. XRD patterns confirm that all of the specimens present a single hexagonal CaCu5-type structure and an increased lattice parameters with increasing Co content. The FWHM of the main peak of melt-spun ribbons reduces because of more homogeneous composition and less lattice strain defects.

Microstructure and Magnetic Properties of (Nd, Pr)_(10.5)(Fe,Zr)_ ( 83.5-x)Co_xB_6 Alloys

Effects of addition of Co on the microstructure and magnetic properties of the series of (Nd, Pr)_ 10.5(Fe, Zr)_ 83.5-xCo_xB_6 alloys, which were prepared by over-quenching and post annealing method, were investigated. The free surface microstructures of crystallized ribbons were observed by means of Atom force microscopy (AFM). The significant improvement of remanence B_r and maximum energy product (BH)_m by Co addition is attributed to the increase of each phase magnetization and the exchange-coupling regions between the soft and hard magnetic phases. However, Co addition decreases the intrinsic coercivity (H_ ci), resulting from the grain coarsening and the (Nd,Pr)_2Co_ 14B phase, which has less anisotropy field (HA) at room temperature. The value of 2%(atom fraction) of Co addition is optimal. The bonded magnets of (Nd,Pr)_ 10.5(Fe,Zr)_ 81.5Co_2B_6 has the best combination of properties, which are B_r=0.662 T, H_ ci=616 kA·m -1 and (BH)_ max=74.0 kJ·m -3.

Magnetization Anisotropy in Amorphous Nd_8Fe_(86)B_6 Ribbons

Crystalline, partial and complete amorphous Nd_8Fe_(86)B_6 ribbons were prepared by melt spinning with different wheel speeds from 7 to 43 m·s^(-1). All the ribbons exhibited anisotropy in magnetization, which unusually increased when the ribbons changed from crystalline to amorphous states and slightly decreased when the quenching speeds were higher than 38 m·s^(-1). The experiments reveal that the anisotropy of amorphous ribbons is inherited after crystallization. It is understood that the anisotropy in magnetization of amorphous Nd_8Fe_(86)B_6 ribbons is responsible for the preferred orientation of spontaneous magnetization vectors of Nd-Fe-B clusters.

Effect of annealing process on magnetic properties of Sm(Co_(0.6)Fe_(0.27)Cu_(0.1)Zr_(0.03))_(7.5) ribbons

Sm（Co0.6Fe0.27Cu0.1Zr0.03）7.5 ribbons were prepared by melt-spun method.The results showed that the remnant magnetization Mr and intrinsic coercivity Hci had a rapid increase when the heating rate increased from 5 to 10 °C/min.But the increase of Mr and Hci were observed to be very little when the heating rate was further increased to 20 °C/min.10 °C/min was the critical heating rate for obtaining high magnetic properties.The maximum values of Mr and Hci reached 0.70 T and 780.1 kA/m when the annealing temperature and annealing time were optimized to be 800 °C and 1 h, respectively.Proper second-step heat treatment could suppress the decrease of Hci when the cooling rate increased from 0.7 to 5 °C/min, which could reduce the cooling time effectively.

Magnetization reversal in Fe_(48) Pt_(34) B_(18) magnetic foils

Exchange-spring magnet L1-FePt/（Fe2B＋a-Fe） is fabricated by flash annealing a melt-spun Fe48Pt34B18 foil. A coercivity of 8500 Oe （1Oe = 79.5775 A/m）, squareness （Mr/Ms） of 0.70, saturation magnetization of 10.2 kGs （1 Gs = 10-4 T） and an effective anisotropy Keg = 2.0 × 10^7 ergs/cm3 are obtained. A two-step magnetization reversal feature is characterized in this paper. An exchange bias phenomenon is also observed in a low saturation field.

Magnetic properties and structures of Y-substituted Nd-Y-Fe-B melt-spun ribbons

The nanocrystalline magnetic ribbons of(Nd_(1-x)Y_(x))_(14.5)Fe_(ba1)B(6)Co_(0.2)Al_(1)Cu_(0.15)(x=0,0.1,0.2,0.3,0.4) were prepared by melt-spinning technique.The magnetic properties and microstructures were systematically investigated for the ribbons.It is found that Y substituting Nd in the R_(2)Fe_(14)B main phase grains gives rise to the decrease in the crystal lattice constant.When Y content increases from x=0 to x=0.4,the remanence and intrinsic coercivity(H_(cj)) decrease from 0.80 to 0.71 T and1400 to 809 kA·m^(-)1,respectively,with the corresponding descent rate of 11.5% and 42.5%.It is impressed that the average grain size increases with Y content increasing.And the strong intergrain exchange coupling interactions exist in all the ribbons and could be enhanced with an appropriate Y substitution,such as x=0.4.Moreover,magnetization reversal mechanism is confirmed to be pinning type for the ribbons.The results provide valuable reference to the fabrication of Y-substituted Nd-Y-Fe-B sintered magnets.

Phase and microstructure of TbCu_(7-)type SmFe melt-spun powders

The SmxZr0.3Fe9.1-xCoo.6 （x=0.8, 0.9, 1.D） powders were prepared by melt-spun method with different quenching velocities. The phase and microstructure were studied by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission elec- tron microscopy （TEM）. The Th2Zn17-type structure of the as-cast state changed to TbCuv-type after quenching to a rotating molyb- denum roll under certain velocity, and the formation of TbCuT-type phase was strictly depending on the Sm content and roll speed. The SEM morphology showed that the Fe-rich Zone was typically fish-bone structure and TEM diffraction pattern indicated the nano-scale crystal size with TbCuT-structure when x=0.9, and FCC type 7-Fe on the basis of ct-Fe formed in the non-equilibrium so- lidification could be detected by selected area electron diffraction （SAED） indexing in the x=0.8 samples.

Magnetocaloric effect in ErNi2 melt-spun ribbons

ErNi2 ribbons were produced by rapid solidification using the melt spinning technique.Their structural,magnetic and magnetocaloric properties in the as-solidified state were studied by X-ray diffraction,scanning electron microscopy,magnetization and specific heat measurements.Samples are single phase with the MgCu2-type crystal structure,a Curie temperature TC of 6.8 K and a saturation magnetization at2 K and 5 T of 124.0 A·m2/kg.For a magnetic field change μ0△H of 5 T(2 T) ribbons show a maximum magnetic entropy change |△SMpeak| of 24.1(16.9) J/(kg·K),and an adiabatic temperature change △Tadmax of8.1(4.4) K;this is similar to the previously reported literature for bulk alloys that were processed through conventional melting techniques followed by prolonged thermal annealing.In addition,the samples also show slightly wider △SM(T) curves with respect to bulk alloys leading to a larger refrigerant capacity.

Magnetic properties of melt-spun ribbons(Sm1-xZrx)(Fe0.92Ti0.08)10 with ThMn12 structure and their hydrides

The structure and magnetic hysteresis properties of the cast Sm1-xZrx(Fe0.92Ti0.08)10(x = 0-0.3)alloys and melt-spun ribbons prepared from them were studied.In the cast alloy with x>0.2, a considerable amount of the eutectic phase is found in the SEM micrographs.Analysis of the temperature dependences of the magnetic susceptibility and XRD patterns allows amorphous state in the as-spun ribbons with x>0.2 to be determined.The specific magnetization measured in a field of 17 kOe and remanence decrease with increasing annealing temperature from 800 to 900 ℃ and weakly depend on Zr concentration.The maximal value of coercivity Hc = 4.7 kOe is obtained on the ribbons with x = 0.2 after annealing at 850℃ for 10 min.After additional hydrogenation of the ribbons,both the coercivity and remanence increase by 54% and 7%,respectively.

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 equa-tionT（x,t）=Tmoexp[-k（x-x0）-k2αt]＋T0. The temperatureT（x,t） of the alloy melts decreased with increased positionx and cooling timet exponentially from the wheel-free surface to the wheel-side surface. The constantk determined the decrease speed of alloy tempera-tureT（x,t）, which was proportional to the interfacial heat transfer coefficienth and the interfacial area of heat conductionA0, but in-versely proportional to the thermal conductivityK.x0 was the thickness of the alloy melt. With increasedx0, the temperature differ-ence between wheel-free surface and the wheel-side surface became larger, which would lead to larger difference in grain size. In ex-periments, 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 investi-gated 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.

Helium ions irradiation-induced surface damage in Fe-based melt-spun ribbons

The Fe78Si8B14 and Fe78P8B14 ribbons with different wheel speeds were prepared by melt-spinning, and their responses to He＋ ion irradiation were investigated. Previous studies had shown that the ion beam resistance capability of amorphous ribbons was better than their corresponding crystalline counterparts. However, no significant changes on the surface at low fluence are observed. At a relatively higher fluence, both the ribbons prepared at low and high wheel speeds behave the similar irradiation responses： peeling, flaking and multi-layer damages occur. The fully amorphous ribbons prepared at a high wheel speed can accommodate partial incident ions owing to the inherent disordered structure. As the irradiation fluence increases, they fail to accommodate the excess incident ions, which easily aggregate to result in the surface damage. While the partial amorphous ribbons prepared at a low wheel speed possess lots of unstable crystalline grain boundaries owing to the precipitation of Si-or P-rich phase, which may act as the source for the irradiation-induced defects annihilation. Results show that the size and the fraction of precipitate phases in amorphous matrix may play a dominated role in resisting the ion irradiation.