Influence of Fe Content on Microstructure and Magnetic Properties of Melt-Spun SmCo-Based Alloy Ribbons

The microstructure and magnetic properties of melt-spun Sm(Co_0.88-xFe_xCu_0.10Zr_0.02)_7.5 (x = 0.1 and 0.2) alloy ribbons have been studied. The results showed that the as-spun ribbons were in a single phase, SmCo₇, with the Cu₇Tb structure. When aged in the temperature range from 720 to 900 °C, the SmCo₇ phase transformed into Sm₂Co₁₇, SmCo₅, and CoFe(Zr) phases with a minor Sm₂Co₃ phase. For the x = 0.1 alloy, a large coercivity, H_c = 8.7 kOe, was observed although the soft magnetic CoFe(Zr) phase was present in the alloy. The volume fraction of the CoFe(Zr) phase increased when the ageing temperature increased from 720 to 760 °C. At higher ageing temperature, the CoFe(Zr) phase was partially re-dissolved. With an increase in the Fe content in the alloy, the CoFe(Zr) phase increased significantly, causing the coercivity to decrease.     

Magnetic properties of melt-spun ribbons(Sm_(1-x)Zr_x)(Fe_(0.92)Ti_(0.08))_(10) with ThMn_(12) structure and their hydrides

The structure and magnetic hysteresis properties of the cast Sm_(1-x)Zr_x(Fe_(0.92)Ti_(0.08))_(10)(x = 0-0.3)alloys and melt-spun ribbons prepared from them were studied.In the cast alloy with x0.2, 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 x0.2 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.     

Fabrication of SmCo_5 alloy via cobalt-induced calciothermic reduction and magnetic properties of its ribbon

SmCo_5 alloy was prepared via direct calciothermic reduction using anhydrous samarium fluoride(SmF_3)as raw material and cobalt as inducer.Results of the thermodynamic calculation show that the direct reduction of cobalt-induced SmF_3 for preparing SmCo_5 alloy is feasible.An alloy with 33.89 wt%samarium and a yield of 96.45% were achieved under the optimal conditions of 10% and 20% excess of SmF_3 and calcium over the stoichiometry,respectively,and 1450℃ for 4 min.The X-ray diffraction results show that the reduction products are SmCo_5 alloy and CaF_2.The scanning electron microscopy micrograph of the SmCo_5 alloy ingot exhibits a distinct dendritic morphology composed of samarium and cobalt.The X-ray photoelectron spectroscopy shows that the atomic ratio of samarium to cobalt is approximately 1:5 and both elements demonstrate zero valency(Sm~0,Co~0).The magnetic properties measurement of the SmCo_5 alloy melt-spun ribbon shows the remanent magnetization B_r=0.59 T,intrinsic coercivity H_(Ci)=345.82 kA/m and maximum magnetic energy density(BH)_(max)=42.20 kJ/m~3.These results may be helpful for the development of novel valence-variable rare-earth alloys.     

Microstructure evolution and coercivity mechanism of hydrogenation-disproportionation-desorption-recombination (HDDR) treated Nd-Fe-B strip cast alloys

In this paper, we systematically investigated the microstructure evolution and coercivity mechanism of hydrogenation-disproportionation-desorption-recombination (HDDR) treated Nd-Fe-B strip cast alloys by transmission electron microscopy (TEM) and three-dimensional atom probe (3DAP) analyses. The rod-like NdH_2+x phases with diameters of 10–20 nm are embedded into α-Fe matrix, which hereditarily leads to textured grains in HDDR alloy. The migration of NdH_2+x from Nd-rich region to α-Fe matrix during hydrogen absorption process contributes to the uniform redistribution of Nd-rich phases after HDDR treatment. The HDDR alloy with single domain grain sizes of 200–300 nm exhibits relatively low coercivity of 1.01 T that arises from pinning magnetic domain motion. The weak c-axis orientation of HDDR alloy results in a lower reverse magnetic field (coercivity) to reduce remanence to 0. Moreover, the direct contact of Nd₂Fe₁₄B grains and the high concentration of ferromagnetic elements (Fe content ≈ 66.06 at%, Co content ≈ 0.91 at%) in Nd-rich grain boundary layer lead to strong magnetostatic coupling effect among Nd₂Fe₁₄B grains. The nano-sized α-Fe inside Nd₂Fe₁₄B matrix makes the magnetization reversal easily and decreases the coercivity of HDDR alloy.     

Magnetic properties and magnetization behavior of SmCo-based magnets with TbCu7-type structure

The nanocrystalline magnets with nominal compositions of Sm1-xLuxCo6.8Zr0.2(x=0,0.2,0.4,0.6)were prepared directly by the intensive milling.The effects of Lu content on the phase structure,the magnetic properties,and magnetization behaviors were also investigated.The XRD patterns of the as-milled samples showed a single SmCo7 phase with TbCu7 structure.Lu addition was proved to result in relevant improvements in the microstructure and magnetic properties,especially in the maximum energy product(BH)max.It was shown that a higher maximum energy product and coercivity of about 17.47 kJ/m3 and 473.45 kA/m were obtained in the sample with x=0.2.From the analysis of the magnetization reversal behavior,it was found that a stronger intergrain exchange coupling interaction was observed in the samples with Lu-doping.From the studies of the coercivity mechanism,it was shown that nucleation model was the dominant magnetization reversal process at the elevated temperature.     

Coercivity kinetics upon step annealing of sintered Sm(Co_(0.88-x)Fe_xCu_(0.09)Zr_(0.03))_7 magnets

Behavior of the coercivity of the high-temperature Sm(Co_(0.88-x)Fe_xCu_(0.09)Zr_(0.03))_7 magnets depending on the temperature and time of annealing with the temperature decreasing stepwise from 700 to 400℃ was investigated.It is shown that the growth rate of coercivity abruptly increases at the initial stage of annealing in the vicinity of the Curie temperature of the SmCo_5 phase.The origin of the effect is the counter diffusion of Cu and Co atoms through dislocation tubes,which form because of enhanced stresses and a partial breakage of coherent coupling at the interface of the Sm_2 Co_(17) and SmCo_5 phases.Diffusive enrichment of the SmCo_5 phase in Cu close to the interface with Sm_2 Co_(17) leads to relaxation of stresses and increases in the gradient of the magnetic domain-wall energy and coercivity.     

Effect of La–Y co-substitution on magnetic properties and microstructure of NdFeB alloy ribbons

Committed to obtaining cost-effective NdFeB based permanent magnets, Nd_27–xLa₃Y_xFe_balAl_0.1Cu_0.1B₁ (x = 0–3) alloys were fabricated to detect the magnetic properties and microstructure. When x = 1.8, coercivity of 1004 kA/m and the magnetic remanence of 0.75 T are obtained, which are close to those of the original Nd₃₀Fe_balAl_0.1Cu_0.1B₁ alloy ribbons. The temperature coefficient of coercivity (β) and the temperature coefficient of remanence (α) of the LaY-substituted alloys are better than those of the original alloys. The research results manifest that La is mainly distributed in the grain boundary phases and plays the role of refining the main grains, optimizing the grain boundary phases and improving the wettability between the main phases and the grain boundary phases, while Y tends to enrich in the main phases and enhances the short-range exchange coupling.     

Effects of adding different types of carbon on the structure and magnetic properties of SmCo6.9Hf0.1 alloy

In this paper,SmCo6.9 Hf0.1 as-cast alloys and ribbons with the addition of either graphite（C） or carbon nanotubes（CNTs） were prepared by arc melting and melt-spinning,respectively.The effects of adding carbon on the structure and magnetic properties SmCo6.9 Hf0.1 were investigated by means of X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,magnetic force microscopy（MFM） and vibrating sample magnetometer（VSM）.It was found that the microstructure and magnetic structure of SmCo6.9 Hf0.1 ribbons were changed obviously due to the introduction of C or CNTs,although their crystal structure was characterized as the same Sm（Co,Hf）7 single phase,no matter carbon was added or not.As a result,the magnetic properties of carbon-contained ribbons were enhanced in a certain degree.This was considered to be related to the refined equiaxed grains,small domain size and the pinning effect of C or CNTs-rich regions.The magnetic properties of SmCo6.9 Hf0.1（CNTs）0.05 ribbons reached Hc =12.5 kOe,Mr =57.0 emu/g and Mr/M2 T =0.788.     

Effect of Al on the Structure and Magnetic Properties of Nanocrystalline FeSiBPCu Melt-Spun Ribbons

In this work, we have studied the effects of the addition of Al on the structure, thermal behavior and magnetic properties of rapidly solidified Fe_83.3(Si_0.25B_0.562P_0.188)_16?xCu_0.7Al_x (x = 0, 0.5, 1 and 1.5) melt spun ribbons prepared by single roller melt-spinning process. All of the samples were studied using various techniques such as X-ray diffraction (XRD), differential scanning calorimetry, vibrating sample magnetometer and B-H loop tracer. The average crystallite sizes obtained for the Al-added samples were in the range of 10–18 nm confirmed by XRD results. Thermal analysis results revealed that by adding Al up to 1 at.%, the first crystallization peak shifted towards lower temperature and second peak to the higher temperature compared to the sample without Al. The highest maximum saturation magnetization (1.8 T) was obtained for the 0.5 at.% Al added alloy. Also the magnitude of coercivity was lowest for 1 at.% Al-added alloy. This was mainly related to the decrease of magnetostriction and magnetocrystalline anisotropy substitution of Al atoms for Si, P and Fe in the structure of bcc-Fe.     

Effect of niobium substitution on microstructures and thermal stability of TbCu7-type Sm–Fe–N magnets

This paper reports crystal structures, magnetic properties and thermal stability of TbCu7-type Sm_(8.5)Fe_((85.8-x)Co_(4.5)Zr_(1.2)Nb_x(x = 0-1.8) melt-spun compounds and their nitrides, investigated by means of X-ray diffraction, vibrating sample magnetometer, flux meter and transmission electron microscope. It is found that the lattice parameter ratio c/a of TbCu_7-type crystal structure increases with Nb substitution, which indicates that the Nb can increase the stability of the metastable phase in the Sm-Fe ribbons. Nb substitution impedes the formation of magnetic soft phase a-Fe in which reversed domains initially form during the magnetization reversal process. Meanwhile, Nb substitution refines grains and leads to homogeneous micro structure with augmented grain boundaries. Thus the exchange coupling pining field is enhanced and irreversible domain wall propagation gets suppressed. As a result, the magnetic properties are improved and the irreversible flux loss of magnets is notably decreased. A maximum value 771.7 kA/m of the intrinsic coercivity H_(cj) is achieved in the 1.2 at% substituted samples.The irreversible flux loss for 2 h exposure at 120 ℃ declines from 8.26% for Nb-free magnets to 6.32% for magnets with 1.2 at% Nb substitution.     

Effect of the milling time on the magnetic properties of powder compositions of the Sm<Subscript>2</Subscript>Fe<Subscript>17</Subscript>N<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> intermetallic compound and an Nd–Fe–B alloy

The effect of the wet milling time on the magnetic properties of powder compositions consisting of the hard magnetic Sm₂Fe₁₇N _x (x = 2.9–3.0) nitride and a rapidly quenched Nd_9.6Fe_76.3Co_4.3Zr_3.4B_6.4 (at %) alloy, which are taken in different mass proportions, is studied. The compositions containing no more than 20 wt % alloy are found to exhibit a substantial increase in the magnetic characteristics as compared to those of the nitride. It is shown that the determining effect on the coercivity is related to the degree of structural imperfection of Nd–Fe–B powders, whereas the specific remanent magnetization and the specific magnetization in a field of 2 T are determined by the corresponding characteristics of the alloy. The optimum composition and efficient treatment conditions for powder mixtures are determined.     

The microstructure and magnetization reversal behavior of melt-spun (Nd1−xCex)-Fe-B ribbons

In this study,the alloy ingots with nominal compositions of(Nd_(1-x)Ce_x)_(31)Fe_(bal)Co_(0.2)Ga_(0.1)B(x=0, 0.1 wt%,0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%) were prepared and then melt-spun to form nanocrystalline ribbons at the wheel speed of 20 m/s. XRD results show that all melt-spun ribbons exhibit the tetragonal structure(Nd,Ce)_2 Fe_(14)B phase with the space group P42/mmm. The Curie temperature and lattice constant decrease with the increase of Ce content. The Curie temperature decreases gradually from 306 to 247 ℃with the increase of Ce content. Those results indicate that Ce element has been incorporated into Nd_2 Fe_(14)B main crystalline phase and formed(Ce,Nd)-Fe-B hard magnetic phase. It is also found that the remanence ratio(M_r/M_s) decreases from 0.693 to 0.663 and the coercivity(H_c) decreases from 18.7 to14.2 kOe with the increase of Ce content. However, a relatively high coercivity of 18.3 kOe for(Nd_(1-x)Ce_x)_(31)Fe_(bal)Co_(0.2)Ga_(0.1)B(x = 0.2) melt-spun ribbon is achieved. The coercivity is sensitive to microstructure. The AFM patterns show the sample(x = 0.2) has the most uniform and finest microstructure. The magnetization reversal behavior(δM plots) is discussed in detail. The positive δM value is observed in every sample, which confirms the existence of exchange coupling interaction. Evidently, theδM maximum value reaches 0.9 in the sample(x = 0.2). It is indicated that the intergranular exchange coupling effect is the strongest, which is consistent with coercivity enhancing.     

Fatigue Life of Cast Titanium Alloys Under Simulated Denture Framework Displacements

The objective of the study was to evaluate the hypothesis that the mechanical properties and fatigue behavior of removable partial dentures (RPD) made from cast titanium alloys can be improved by alloying with low-cost, low-melting elements such as Cu, Al, and Fe using commercially pure Ti (CP-Ti) and Ti-6Al-4V as controls. RPD specimens in the form of rest-shaped, clasp, rectangular-shaped specimens and round-bar tensile specimens were cast using an experimental Ti-5Al-5Cu alloy, Ti-5Al-1Fe, and Ti-1Fe in an Al₂O₃-based investment with a centrifugal-casting machine. The mechanical properties of the alloys were determined by performing tensile tests under a controlled displacement rate. The fatigue life of the RPD specimens was tested by the three-point bending in an MTS testing machine under a cyclic displacement of 0.5 mm. Fatigue tests were performed at 10 Hz at ambient temperature until the specimens failed into two pieces. The tensile data were statistically analyzed using one-way ANOVA (α = 0.05) and the fatigue life data were analyzed using the Kaplan-Meier survival analysis (α = 0.05). The experimental Ti-5Al-5Cu alloy showed a significantly higher average fatigue life than that of either CP-Ti or Ti-5Al-1Fe alloy (p < 0.05). SEM fractography showed that the fatigue cracks initiated from surface grains, surface pores, or hard particles in surface grains instead of the internal casting pores. Among the alloys tested, the Ti-5Al-5Cu alloy exhibited favorable results in fabricating dental appliances with an excellent fatigue behavior compared with other commercial alloys.     

Magnetic Alignment Study of Hybrid Magnet Consisting of R-Rich and R-Lean Nd-Fe-B Alloys

A hybrid magnet was prepared by the hot-pressing and die-upsetting of the mixture of the R-rich Nd_xFe_93.5–xGa_0.5B₆ (x= 13.5 and 11.8) alloy and the R-lean Nd_xFe_93–xNb₁B₆ (x = 6, 9) alloy melt-spun ribbons. The microstructure and magnetic properties of the hybrid magnet were investigated. In the hot-pressed or die-upset hybrid magnet the R-rich and R-lean alloy regions existed independently without alloying between them. The two alloy regions in the die-upset hybrid magnet were coupled effectively via a magnetostatic interaction. A texture was developed only in the R-rich Nd₂Fe₁₄B single phase alloy region in the die-upset hybrid magnet, and this led to an anisotropic nature in die-upset hybrid magnet. The die-upset hybrid magnets containing higher Nd-content (13.5 at%) host alloy shows consistently a better magnetic alignment with respect to the magnets with lower Nd-content (11.8 at%) host alloy.     

Characterization of Microstructure and Magnetic Properties of NdFeB Magnet with Dy, Al and Cu Additions

A new alloy of Nd33.5Dy0.99Febal.Al0.52Cu0.1B1.15 (%, mass fraction) was fabricated by powder metallurgy. The effects of Dy, Al and Cu additions on the microstructure and magnetic properties of sintered NdFeB magnet were investigated. The additions of Dy, Al and Cu are effective to refine grains and improve coercivity. Moreover, suitable amounts of Dy, Al and Cu lead to a demagnetization curve with good rectangularity. It is found that the sintered NdFeB magnet has relatively high magnetic performance of Br=12.17kGs, jHc=13.52kOe and (BH)max=34.71MGOe. The sintered NdFeB sample was examined by magnetic force microscope which revealed the domain structures at the surface. It is revealed that the mean Nd2Fe14B grain size is significantly larger than the average scale of the magnetic contrast. An explanation about this is that most Nd2Fe14B grains in sintered NdFeB alloy are dominated with the muhidomain structures when the magnet is in thermally demagnetization state.     

Structure, Properties, and Glass Forming Ability of Melt-Spun Fe-Zr-B-Cu Alloys with Different Zr/B Ratios

Melt-spun ribbons of Fe_99–x–y Zr _x B _y Cu₁ alloys with x + y = 11 and x + y = 13 were prepared under similar experimental conditions and characterized for structure and soft magnetic properties. Substitution of Zr by B changes the structure of as-spun ribbons from completely amorphous to cellular bcc solid solution coexisting with the amorphous phase at intercellular regions and then to completely dendritic solid solution. The glass forming ability (GFA) of the Fe-Zr-B-Cu system, evaluated from thermodynamic properties such as enthalpy of mixing and mismatch entropy, is found to be in good agreement with the experimental observations. Annealing of all ribbons leads to the precipitation of nanocrystalline bcc α-Fe phase from both amorphous phase and already existing bcc solid solution. A window of alloy compositions that exhibit the best combination of soft magnetic properties (high saturation magnetization and low coercivity) was identified.     

Coercivity enhancement of nanocrystalline hot-deformed Nd-Fe-B magnets by low-melting eutectic MM-Cu(MM=La,Ce,Pr,Nd) alloys addition

MM_(85)Cu_(15)(MM = La,Ce,Pr,Nd) eutectic alloys were added into the hot-deformed Nd-Fe-B magnets to enhance the coercivity.It is found that three endothermic peaks occur on the differential scanning calorimetry curve of the MM-Cu melt-spun ribbons at 432.2,451.1 and 516.5℃.The peaks substantially correspond to three types of MM-Cu low-melting eutectic phase.The coercivity of magnets increases when the MM-Cu content is lower than 4 wt%,and then keeps almost no change with the content further increasing to 5 wt%.The coercivity of the hot-deformed magnets with 4 wt% and without MM-Cu addition is 948 and 683 kA/m,respectively.Nearly all the platelet-shaped grains are isolated by the thickened intergranular phase after MM-Cu addition.Moreover,the average grain size of the magnets with MM-Cu addition decreases compared with that of the magnet without MM-Cu addition.Scanning electron microscopy images show that the areal fraction of the RE-rich grain boundary phase increases from 8.6% to 15.1% after MM-Cu addition.The La,Ce together with Cu and Ga aggregate at the grain boundary regions separating neighboring grains and smoothing the grain boundaries.Therefore,both the thickened grain boundary and decreased mean grain size result in the enhancement of coercivity after MM-Cu eutectic alloy addition.     

Rotating magnetocaloric effect and thermal transport properties in sintered Nd_(0.8)Pr_(0.2)Co_5 alloy

We report microstructure,magnetocaloric effect and thermal transfer properties of highly orientated Nd_(0.8)Pr_(0.2)Co_5 alloy prepared by powder metallurgical processing.Two spin-reorientation transitions of easy magnetization direction,easy plane to easy cone at T_(SR1)=206 K,easy cone to easy axis at T_(SR2)=242 K,are observed.The present textured alloy exhibits a rotating entropy change of 2.6 J/(kg·K)and refrigerant capacity of 155 J/kg under a magnetic field of 2 T,and high thermal conductivity of 11 W/(m·K).The sintered Nd_(0.8)Pr_(0.2)Co_5 alloy with good combination of excellent magnetocaloric and thermal transfer properties are promising for scientific research and practical applications as room-temperature rotating magnetic refrigeration materials.     

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 NdxFe94-xB6 (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 Nd2Fe14B 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 Nd2Fe14B 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.     

Relationship between controllable preparation and microstructure of NdFeB sintered magnets

The double hard magnetic phase magnets with nominal compositions of Nd_30–xDy_xFe₆₉B₁(x=2, and 4) (wt.%) were prepared. The magnetic properties of the magnets were measured with a NIM-2000H hysteresigraph. The crystalline structures of the magnets were identified by X-ray diffraction (XRD). The Rietveld refinement was carried out using the FULLPROF software. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses were carried out in order to investigate the microstructure of the magnets. It showed that the magnets consisted mainly of Nd₂Fe₁₄B phase, and some Nd-rich phase. Two types of matrix-phase grains in dark grey and light grey were found in the magnets with x=2 and 4. The Dy content was obviously different in the two types of grains, which proved that the double hard magnetic phases (Dy-rich and Dy-lean phases) coexisted in the magnet. It revealed that the Nd-rich phases in junction regions had fcc structure, with the unit cell parameter of about 0.52–0.56 nm. The weak superlattice spots were found in the SAD patterns of the junction Nd-rich phases with large scale. The double hard magnetic phase structure seemed to improve the magnetic properties of NdFeB magnets with high coercivity, while decrease the consumption of Dy element, compared with the single alloy magnet.