Microstructural characteristics of Nd2Fe14B/α-Fe nanocomposite ribbons bearing Nb element

The effects of Nb on the microstructure and magnetic properties of (Nd0.9Dy0.1)9.5Fe79-xCo5NbxB6.5(x=0, 1) nanocomposite magnets were investigated. A fine and uniform microstructure was achieved for the ribbons annealed at 710℃ for 4min, enhancing the interaction coupling between grains and improving the magnetic properties. The results of three-dimensional atom probe (3DAP) indicated that Fe-Nb-B inter granular phase existed at the grain boundaries, suppressing the grain growth during the crystallization process. The coercivity was improved from 224 to 643 kA/m for the modification of the microstructure.     

Improvement of microstructure and mechanical properties of TiAl−Nb alloy by adding Fe element

In order to improve mechanical properties and optimize composition of TiAl−Nb alloys, Ti46Al5Nb0.1B alloys with different contents of Fe (0, 0.3, 0.5, 0.7, 0.9, and 1.1 at.%) were prepared by melting. Macro/microstructure and compression properties of the alloys were systematically investigated. Results show that Fe element can decrease the grain size, aggravate the Al-segregation and also form the Fe-rich B2 phase in the interdendritic area. Compressive testing results indicate that the Ti46Al5Nb0.1B0.3Fe alloy shows the highest ultimate compressive strength and fracture strain, which are 1869.5 MPa and 33.53%, respectively. The improved ultimate compression strength is ascribed to the grain refinement and solid solution strengthening of Fe, and the improved fracture strain is due to the reduced lattice tetragonality of γ phase and grain refinement of the alloys. However, excessive Fe addition decreases compressive strength and fracture strain, which is caused by the severe Al-segregation.     

Structural and magnetic properties of backward extruded Nd–Fe–B ring magnets made by different punch chamfer radius

Radially oriented Nd–Fe–B ring magnets were prepared by backward extrusion of MQ-C powder. The punch chamfer radius has a great impact on the microstructure and magnetic properties of the ring magnet. With the chamfer radius changing from 2, 5 to 8 mm, the cracks in the inner wall decrease obviously while the crystallographic alignment drops. Furthermore, the mechanism of caxis growth was suggested to be a combination of shear deformation in the corner and solution-precipitation under the stress parallel to radial direction. The alignment drops on the top of ring because the grains grow freely and some textured grains grow through nucleation and recrystallization. In the present work, the optimal punch chamfer radius is found to be 2 mm, and in this case, the remanence,coercivity, and maximum energy product of the ring magnet achieve 1.4 T, 670 kJám, and 342 kJám,respectively.     

Dynamic stress–strain properties of Ti–Al–V titanium alloys with various element contents

A series of Ti–Al–V titanium alloy bars with nominal composition Ti–7Al–5V ELI,Ti–5Al–3V ELI,commercial Ti–6Al–4V ELI and commercial Ti–6Al–4V were prepared.These alloys were then heat treated to obtain bimodal or equiaxed microstructures with various contents of primary a phase.Dynamic compression properties of the alloys above were studied by split Hopkinson pressure bar system at strain rates from 2,000 to 4,000 s-1.The results show that Ti–6Al–4V alloy with equiaxed primary a(ap)volume fraction of 45 vol%or 67 vol%exhibits good dynamic properties with high dynamic strength and absorbed energy,as well as an acceptable dynamic plasticity.However,all the Ti53ELI specimens and Ti64ELI specimens with ap of 65 vol%were not fractured at a strain rate of4,000 s-1.It appears that the undamaged specimens still have load-bearing capability.Dynamic strength of Ti–Al–V alloy can be improved as the contents of elements Al,V,Fe,and O increase,while dynamic strain is not sensitive to the composition in the appropriate range.The effects of primary alpha volume fraction on the dynamic properties are dependent on the compositions of Ti–Al–V alloys.     

The effects of long term annealing at 1000°C for 24 h on the microstructure and magnetic properties of Pr–Fe–B/Nd–Fe–B magnets based on Nd16Fe76B8 and Pr16Fe76B8

Magnets produced via a hydrogen decrepitation/roller-milling route have been subjected to a post sintering heat treatment of 1000°C for 24 h. Alloys of nominal composition Pr₁₆Fe₇₆B₈ and Nd₁₆Fe₇₆B₈ have been studied in terms of both microstructure and magnetic properties to determine the influence of this 24-h annealing treatment. The effect of annealing the Pr₁₆Fe₇₆B₈ magnets at 1000°C for up to 24 h resulted in a general increase in the overall magnetic properties, especially in the intrinsic coercivity. In contrast to these observations, the same heat treatment was found to be detrimental to all the magnetic properties of the Nd₁₆Fe₇₆B₈ magnets.     

Magnetic properties of sputtered anisotropic Pr–Fe–B thin films with different structures and antiferromagnetic materials

Anisotropic Pr–Fe–B films with soft-magnetic layer(Fe) and/or antiferromagnetic layer(Mn, Fe Mn or Mn O) were prepared by direct-current(DC) magnetron sputtering on Si(100) substrates heated at 650 °C. The influence of four types' different structures on the magnetic properties of Pr–Fe–B films was investigated.The phase and magnetic properties were characterized by means of X-ray diffraction(XRD) and superconducting quantum interference device(SQUID). Addition of antiferromagnetic layer enhances both the coercivity and the remanence ratios of Pr–Fe–B films with suitable structures. The interface number increases and the antiferromagnetic–ferromagnetic exchange interaction is likely to become stronger, which affect the improvement of magnetic properties. To further understand the influence of structures with soft-magnetic Fe layer and/or antiferromagnetic Fe Mn layer on the magnetic properties of Pr–Fe–B hard-magnetic films, the thickness of Pr–Fe–B layer was designed to decrease from 600 to 50 nm. The improvement of magnetic properties becomes obvious in Mo(50 nm)/Pr–Fe–B(25 nm)Mo(2 nm)Fe Mn(20 nm)Mo(2 nm)Pr–Fe–B(25 nm)/Mo(50 nm) film.     

Effect of Nd content on the microstructure and coercivity of hot-deformed Nd–Fe–B permanent magnets

The microstructure of hot-deformed Nd–Fe–B permanent magnets with different Nd contents was investigated in order to correlate them with the hard magnetic properties. A thick distinct Nd-rich grain boundary (GB) layer was observed in a high Nd content sample by scanning electron microscopy and transmission electron microscopy. Three-dimensional atom probe results showed a significant increase in the Nd content in the GB as the overall Nd content in the alloy increased. We found a clear correlation between the Nd concentration in the GB layer and the coercivity. The mechanism of the coercivity increase is discussed based on the microstructure characterization and micromagnetic simulation results.     

Crystallization behaviour and high coercivity of （Nd,Pr）（13）Fe（80）Nb1B6 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 _i H _c = 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.     

Crystallization behaviour and high coercivity of （Nd,Pr）（13）Fe（80）Nb1B6 melt-spun ribbons

Amorphous (Nd,Pr)13Fe80Nb1B6 ribbons were crystallized at 670-730℃ 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℃, respectively. High eoercivities, with the maximum value of iHc = 1616 kA/m at 700℃ for 19 min, measured by a physical 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 magnetostrictive properties of Tb doped Fe–Ga bulk alloys prepared by melt quenching

The microstructure and magnetostrictive properties were investigated in the Tb doped Fe83Ga17-xTbx(x = 0.05, 0.10, 0.20, 0.30, 0.40, 0.50) bulk rods prepared by melt rapidly quenching. The partial solid solubility of Tb in the Fe–Ga matrix was preliminary detected by the lattice parameters and SEM observation. The matrix keeps A2 structure and the second phase appears surround the grain boundary as x C 0.1. h100 i preferred orientation is also observed for x = 0.1 sample along the axis of the quenched rod. The saturation magnetostriction first increases and maximum value reaches at x = 0.1, and then decreases with Tb addition increasing. The initial increase of the magnetostriction should be associated with the partial solution of Tb in the matrix, the maximum value at x = 0.1 should be attributed to the h100 i preferred orientation, and the decrease of the magnetostriction is correlated with the appearance of the second phase along the grain boundary.     

Site Preferences of Pr and Co in(Nd,Pr)_2(Fe,Co)_(14)B Compounds

The Curie temperature of(Nd_(1-x)Pr_x)_2Fe_(14)Co_yB compounds(x=0,0.2,…,1.0 and y=O,2,4,6,14)hasbeen determined with AC initial susceptibility measurement.It was found that the variations of Curie tempera-ture with x is not linear for y=0 and 14,whereas it is linear for other values of y.The lattice constants of(Nd_(1-x)Pr_x)_2Fet_(14)B were determined by using X-ray diffraction.The lattice expansion was mostly along the caxis,whereas that along the a-axis remained practically zero for the whole series.It is suggested that Pr atomsmay show site preference in R_2M_(14)B compounds(M=Fe or Co).Due to the substitution of Co for Fe.thetendency of site preference of Pr becomes less pronounced,which may be attributed to the decrease of differ-ence of crystal electric field(CEF)acting on the two rare earth sites with the introduction of Co or Fe.In con-trast to that of the Pr atoms,the site preference of Co iu(Nd(1-x)Pr_x)_2Fe(14-y)Co_yB compounds does not depend onthe composition of the rare earth sublattice(R=N d or Pr).     

Effect of post-sinter annealing on the coercivity and microstructure of Nd–Fe–B permanent magnets

To understand the mechanism of the increase in coercivity caused by post-sinter annealing of Nd–Fe–B-based magnets, we have investigated the microstructures of commercial sintered magnets by high-resolution scanning electron microscopy, transmission electron microscopy and atom probe tomography. Continuous thin layers of a Nd-rich amorphous phase were found along the grain boundaries in the post-sinter annealed sample, the chemical composition of which was determined to be Nd₃₀Fe₄₅Cu_24.1B_0.9. A fine Cu-enriched shell was also confirmed in the Nd-rich phase grain, suggesting the Nd₂Fe₁₄B grains are completely enveloped by the Cu- and Nd-enriched layers. Furthermore, a lamellar microstructure of the Cu-enriched phase was confirmed in some Nd-rich phase grains. The mechanism of the coercivity increase caused by post-sinter annealing is discussed based on these characterization results.     

Effect of Ga addition on the microstructure and magnetic properties of hydrogenation–disproportionation–desorption–recombination processed Nd–Fe–B powder

Microstructural evolution of hydrogenation–disproportionation–desorption–recombination processed Nd_12.5Fe_72.8Co_8.0B_6.5Ga_0.2 powder has been investigated in relation to coercivity development during the desorption recombination process. Coercivity increases when residual NdH₂ is completely dehydrogenated and the decomposed Nd is segregated at the grain boundaries of the Nd₂Fe₁₄B phase. Three-dimensional atom probe (3DAP) analysis indicates the segregation of Ga at the grain boundary. The reason for the enhancement of the coercivity by the trace addition Ga is discussed based on the 3DAP results.     

Effects of quenching speed and Joule heating on the magnetic properties of Nd9Fe86B5 ribbons

1 IntroductionNanocomposite two-phase magnets are an im-portant type of permanent magnetic materials that have attracted much attention in recent years. Com-bining the high coercive force of the hard magnetic phase and the large saturation magnetization o…     

Fabrication and soft-magnetic properties of Fe–B–Nb–Y glassy powder compacts by spark plasma sintering technique

Magnetic properties of (Fe_0.72B_0.24Nb_0.04)_95.5Y_4.5 sample were investigated. The sample was produced from glassy powders made by the gas-atomization and consolidation using the spark plasma sintering (SPS) technique. Maximum relative density of 99.5% was achieved in the spark plasma sintered (SPSed) compact due to the viscous flow enhanced by the applied stress even under the glass transition temperature. X-ray diffraction pattern of the compact indicates that the glassy structure was maintained through the SPS process. However, the results of differential scanning calorimetry (DSC) showed that the glass transition temperature and crystallization temperature of the SPSed glassy compact shift to a higher and lower temperature, respectively, that is, a smaller ΔT_x. Saturation magnetization of the SPSed glassy compact became 10% higher than that of the initial glassy powder. The Curie point was enhanced from 522 K for the glassy powder to 548 K for the SPSed glassy compact. Spin-exchange interaction is expected to be enhanced by a short-range scale atomic rearrangement caused by the high applied stress and temperature during the SPS process.     

Recrystallization behavior,microstructure evolution and mechanical properties of biodegradable Fe–Mn–C(–Pd) TWIP alloys

In this study the interplay between recrystallization and precipitation in a biodegradable TWIP (twinning-induced plasticity) steel developed for use in temporary implants was investigated. Microstructural and mechanical properties were studied and a thermomechanical treatment was designed with the aim of achieving an overall performance suitable for the intended application as temporary implant material. The formation of Pd-rich precipitates in the cold-worked state was found to considerably retard recrystallization during an annealing treatment. The formation, morphology and interaction with dislocations of these precipitates were studied by means of scanning and transmission electron microscopy. Grain boundary pinning by Pd-rich precipitates (Zener drag) and reduced dislocation mobility due to a solute drag effect caused by the enrichment of dislocation cores with Pd were both identified as mechanisms which impede recrystallization. A model is reported which explains the interplay between recrystallization and precipitation, and provides the basis for the optimized thermomechanical treatment then presented. The resulting mechanical properties, in particular the combination of high strength and ductility with a pronounced strain-hardening response, exceed the performance of other TWIP steels and alloys typically used in biomedical implants, such as stainless steel, titanium or cobalt–chromium alloys. The specific property profile developed is especially advantageous for the production and deployment of cardiovascular stents.     

Effect of composing element on microstructure and mechanical properties in Mo–Nb–Hf–Zr–Ti multi-principle component alloys

A series of non-equiatomic Mo–Nb–Hf–Zr–Ti alloys are synthesized to investigate the effects of the concentration variation of each composing elements on the microstructure and mechanical properties. It is found that all studied alloys form single body-centered-cubic (BCC) phase only with the variation of the lattice parameter, which indicates that the concentration variation of each composing elements has no effect on the phase constitutes. All studied alloys exhibit typically dendritic and interdendritic structure while the concentration variation of each composing elements has different effects on the microsegregation. The concentration variation of Zr leads to the most serious microsegregation. Elements with a higher melting point such as Mo and Nb solidify preferentially and thus are enriched in the dendrites. Both the increase and decrease of the concentration of each composing element reduce the hardness and strength of non-equiatomic Mo–Nb–Hf–Zr–Ti alloys compared with the equiatomic MoNbHfZrTi alloy.     

A comparative study of microstructure,oxidation resistance,mechanical, and tribological properties of coatings in Mo–B–(N), Cr–B–(N) and Ti–B–(N) systems

M–B–(N) (M = Mo, Cr, Ti) coatings were obtained by the magnetron sputtering of MoB, CrB₂, TiB, and TiB₂ targets in argon and in gaseous mixtures of argon with nitrogen. The structure and composition of the coatings have been investigated using scanning electron microscopy, glow-discharge optical emission spectroscopy, and X-ray diffraction. The mechanical and tribological properties of the coatings have been determined by nanoindentation, scratch-testing, and ball-on-disk tribological tests. The experiments on estimating the oxidation resistance of coatings were carried out in a temperature range of 600–1000°С. A distinctive feature of TiB₂ coatings was their high hardness (61 GPa). The Cr–B–(N) coatings had high maximum oxidation resistance (900°С (CrB₂) and 1000°С (Cr–B–N)) and possessed high resistance to the diffusion of elements from the metallic substrate up to a temperature of 1000°С. The Mo–B–N coatings were significantly inferior to the Ti–B–(N) and Cr–B–(N) coatings in their mechanical properties and oxidation resistance, as well as had а tendency to oxidize in air atmosphere after long exposure at room temperature. All of the coatings with nitrogen possessed a low coefficient of friction (in a range of 0.3–0.5) and low relative wear ((0.8–1.2) × 10^–6 mm3 N^–1 m^–1.