Amorphization and magnetic properties of Fe62Nb38 mechanically alloyed powders

The amorphization and magnetic properties of Fe62Nb38 mechanically alloyed powders were investigated. In the initial mechanical alloying processes, the lattice structure of pure Fe is destroyed due to the cold-welding and fracturing, accompanying the reduction of ferromagnetic properties. The Ms value of Fe62Nb38 powders with ball-milling time t=6 h is only 48.1 A.m^2/kg. With prolongating of mechanical alloying processes, a solid state amorphization reaction (SSAR) takes place and the Fe-Nb ferromagnetic amorphous phase is formed. With the milling time increasing from 6 to 18 h, the saturation magnetization of Fe62Nb38 powders increases with enhancement of the proportion of ferromagnetic amorphous phase in milled powders. The Ms value of the Fe62Nb38 amorphous powders is 98 A.m^2/kg, which is very close to the value estimated from dilute model. However, the Curie temperature of the Fe62Nb38 amorphous phase is only 206℃, which is much smaller than that of the pure Fe. This implies that the exchange interaction between Fe atoms in amorphous alloyed Fe62Nb38 becomes weak due to the Nb dilution. Investigation shows that the variation of magnetic properties of milled powders is one of important tools for describing the amorphization by mechanical alloying.     

Characteristics of mechanically alloyed Cu, C and Cr mixed powders

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Structure and magnetic properties of mechanically alloyed Tb0.2Pr0.8（Fe0.4Co0.6）1.93 and magnetostriction of its epoxy composite

The C15 Laves phase with composition Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93 was synthesized by mechanical alloying (MA) and subsequent annealing process. The structure and magnetic properties of Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93 were investigated by means of X-ray diffraction (XRD), a vibrating sample magnetometer, and a standard strain technique. The effect of annealing on the structure and magnetic properties was studied. The analysis of XRD shows that the high Pr-content Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93 alloy with the single phase of MgCu₂-type structure can be successfully synthesized by MA method. The sample annealed at 450°C is found to have a coercivity of 196 kA/m at room temperature. An epoxy/Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93 composite was produced by a cold isostatic pressing technique. A large magnetostriction of 400 ppm, at an applied magnetic field of 800 kA/m, was found for the composite. The epoxy-bonded Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93 composite combines a high magnetostriction with a significant coercivity, which is a promising magnetostrictive material.     

Structure and intrinsic magnetic properties of Sm_(1-x)Pr_xCo_5(x=0–0.6) compounds

In this work, the effects of Pr content on the structure and intrinsic magnetic properties of Sm_(1-x)Pr_xCo_5(x = 0–0.6) compounds prepared by induction melting were systematically investigated by scanning electron microscopy(SEM), X-ray diffraction(XRD), and magnetic measurements. Microstructural observation and chemical composition analysis show that Sm_(1-x)Pr_xCo_5 compounds are composed of(Sm, Pr)Co(1:5) phase and(Sm, Pr)-rich grain boundary phase. XRD results show that all the Sm_(1-x)Pr_xCo_5 compounds have a(Sm, Pr)_1Co_5 main phase with the hexagonal CaCu_5-type crystal structure and the(Sm, Pr)_2Co_7 impurity phase. In addition, the detailed research shows that the lattice constants(a, c) and unit volume(V) are all enlarged with the increases in Pr content. According to the magnetic measurements, as the Pr content increases to larger than 0.4, both the Curie temperature(T_C) and the anisotropy field(H_A) of all the Prdoped compounds decrease rapidly. Meanwhile, the magnetization of Sm_(1-x)Pr_xCo_5 compounds at applied field of 14 T(M_(14 T)) are observably improved with Pr doping content of x0.3. Among them, Sm_(0.6)Pr_(0.4)Co_5 compound exhibits slightly lower H_Aand T_C, but much higher M_(14 T) than those of the binary SmCo_5, indicating that doping of proper Pr content into SmCo_5 compound can optimize the intrinsic magnetic properties. As a result, the optimal intrinsic magnetic properties of H_A= 29.11 T,T_C= 989 K, and M_(14 T)= 102.31 mA·m~2·g-1are obtained in Sm_(0.6)Pr_(0.4)Co_5 compound.     

Structure,magnetic properties,and thermal stability of Sm1−x Tm x Co5 compounds

Structure, magnetic properties, and thermal stability of ternary Sm1-xTmxCo5 compounds were studied via X-ray diffraction(XRD), thermal magnetic analysis(TMA), and magnetic measurements. XRD results show that all the compounds have a main phase of hexagonal CaCu5-type crystal structure with small amount of impurity phases; increasing Tm content is associated with contraction of the hexagonal unit cell in the direction of the c axis and expansion of the a and b parameters. TMA results indicate that the Curie temperature(TC) of Sm1-xTmxCo5 compounds gets higher with the increase in Tm content.Magnetic measurements show that both the magnetic anisotropy field(HA) and the magnetization at an applied field of 7 T(M7 T) decrease with the increase of Tm content. However, the thermal stability of both the HAand M7 Tof all the Tm doped compounds is remarkably improved compared with that of the pure SmCo5 compound, leading to the result that both the M7 Tand HAof Sm0.8Tm0.2Co5 .2are higher than those of SmCo5 compound at 473 K, which indicates the good potential of Tm doped compound in the practical applications at elevated temperature.     

Structure,magnetic and magnetocaloric properties of RE11Ge8In2 (RE = Gd–Tm)

A new tetragonal Gd₁₁Ge₈In₂ phase has been obtained by arc-melting and annealing at 800 °C. The structure has been determined and refined from single crystal X-ray diffraction data in the I4/mmm space group with a = 11.2091(6) and c = 16.3994(9) Å. Phases with the RE₁₁Ge₈In₂ (RE = Gd–Tm) composition were subsequently synthesized and their structures were refined using X-ray powder diffraction methods. Magnetic measurements carried out on RE₁₁Ge₈In₂ (RE = Gd–Tm) indicated a ferromagnetic ordering in all phases. The magnetocaloric effect in terms of the magnetic entropy change, ΔS_mag, was evaluated for the Gd-, Tb- and Tm-containing samples, and the largest |ΔS_mag| value of 10.6 J/kg K was obtained for Tm₁₁Ge₈In₂.     

Mechanism of depolarization with temperature for <0 0 1> (1 − x)Pb(Zn1/3Nb2/3)O3–xPbTiO3 single crystals

The temperature dependence of polarization for Pb(Zn_1/3Nb_2/3)_1?xTi_xO₃ single crystals poled in the [0 0 1]-direction has been investigated. During the application of a temperature increase, the percentage of switched domains and the distortion of the crystalline lattice in (1 ? x)PZN–xPT single crystals were evaluated by X-ray diffraction (XRD) patterns. Using this method, intrinsic and extrinsic contributions to polarization variations were separated in the temperature range from 25 °C to the Curie temperature (T_c). Experimental polarization variations were simulated from microscopic data and details on micro–macro relationships were given. It was found that polarization variation with temperature is caused by the variation of the distortion of the crystalline lattice for temperatures below the Curie temperature and that only 90° domain switching occurs in the vicinity of the Curie temperature. Moreover, the hysteretic behavior of the polarization with temperature is due to motion of domain walls. The understanding of mechanisms of depolarization with temperature and the hysteresis associated with are of interest for the enhancement the pyroelectric properties of the material for detection and energy harvesting applications.     

Preparation of dense TiN1 − X (X = 0–0.4) by pulsed electric current sintering: Densification and mechanical behavior

Bulks of TiN_1 − X in the range of X = 0–0.4 with high density were prepared by a new method which comprises the reaction between TiN with TiH₂ through pulsed electric current sintering. X-ray diffractograms revealed that single fcc phase with nitrogen vacancies was achieved after sintering; further observation by scanning electron microscopy showed homogeneous structure in all samples and larger grain size by increasing the amount of TiH₂. The maximum Vickers hardness measured on the samples was approximately 31 GPa at X = 0.3. An increase in hardness was observed in non-stoichiometric samples even its larger grain size. The grain size-indent diagonal ratio was calculated from 1.2 at X = 0 to 5.6 at X = 0.4. The addition of TiH₂ showed an improvement in both densification and hardness without significant degradation of fracture toughness. Based on these results, the mechanical properties of TiN_1 − X bulks can be controlled as a function of TiH₂/TiN ratios in order to be used for different applications.     

Structure and magnetic properties of intermetallic compounds Gd5Si2-xGe2-xM2x

1 Introduction Nowadays, there is much interest in magnetic refrigeration materials, as they offer the prospect of an energy-efficient and environment friendly alternative for the traditional vapour cycle refrigeration technique. Magnetic refrigeration is…     

Characterization of mechanically alloyed nanocomposites in TiO2–B2O3–Mg–C quaternary system

The influence of the simultaneous presence of magnesium and graphite on mechanosynthesis of various nanocomposite powders in TiO₂–B₂O₃–Mg–C quaternary system was investigated. A mixture of boron oxide and titanium dioxide powders along with different amounts of magnesium and graphite was milled using a high-energy planetary ball mill to provide necessary conditions for the occurrence of a mechanically induced self-sustaining reaction (MSR). In the absence of C (100 wt.% Mg), TiB₂ nanopowder was formed as a result of combustion reaction after 34 min of milling. In the presence of both Mg and C, the mechanochemical reaction was completed after different milling times depending on the weight fraction of the reducing agents in the powder mixture. In the presence of x wt.% Mg–y wt.% C (x = 85 and 90; y = 100 − x), the mechanosynthesized composites contained TiB₂ and TiC as major compounds as well as MgO and Mg₃B₂O₆ as unwanted phases. With further increasing the graphite content to 30 wt.%, no mechanical activation was observed after 90 min of milling. The nanocomposite powders showed a bimodal particle size distribution characterized by the presence of several coarse particles (≈ 250 nm) along with finer particles with a mean size of about 75 nm. Formation mechanism of nanocomposites was explained through the analysis of the relevant sub-reactions.     

Structure and magnetic properties of Pr0. 1CexTb0.9-xFe1.9 alloys

1　INTRODUCTIONTerfenol D ( Tb0.27 Dy0.73 Fe2 ) exhibits largemagentostriction and minimized magnetic anisotro py at room temperature[1], so it is widely used inactuators and transducers. But the main raw mate rials of Terfenol D are expensive Tb and Dy. Ac cording to the single ion model[2], CeFe2 and PrFe2compounds have larger magnetostriction thanTbFe2 and DyFe2 at 0 K. In addition, Ce and Prare much cheaper than Tb and Dy. So Ce basedand Pr based compo…     

Microstructure,texture and magnetic properties of strip casting Fe–6.2 wt%Si steel sheet

An Fe–6.2 wt%Si strip with equiaxed grains and mild {0 0 1}〈0 v w〉 fiber texture was produced by twin-roll strip casting process. Then the as-cast strip was treated with or without the hot rolling prior to the warm rolling and annealing. When the hot rolling was not introduced, a fine and heterogeneous warm-rolled microstructure was produced and led to a fine recrystallization microstructure and very weak {0 0 1}〈0 v w〉 fiber texture in the annealed sheets. When the hot rolling was introduced, a coarse and homogeneous warm-rolled microstructure was produced and led to a very coarse recrystallization microstructure and much stronger {0 0 1}〈0 v w〉 fiber texture in the annealed sheets. The annealed sheets with hot rolling showed a higher magnetic induction and a higher core loss than those without hot rolling.     

Structure stability and mechanical properties of Mg–Al-based alloy modified with Y-rich and Ce-rich misch metals

Mg–3.4 wt.% Al-based alloy modified with 2.4 wt.% Ce-rich and 0.3 wt.% Y-rich misch metals was prepared by high-pressure die-casting. The microstructure, thermal stability of intermetallic phases and mechanical properties were investigated. The cross-section of test bar is divided into the fine skin region and the wide core region by a narrow band. Two intermetallic phases Al₁₁RE₃ and Al₂RE, with the former being the dominant one, are mainly distributed at the interdendritic regions. The Al₁₁RE₃ intermetallics possess high volume fraction, fine acicular/lamellar morphology and layered arrangement. It is suggests that each rare earth element has the individual preference for the above two Al–RE intermetallics. The thermal stability of Al₁₁RE₃ is conditioned. It is basically stable at temperature up to 200 °C within 800 h, while almost all Al₁₁RE₃ intermetallics transform to Al₂RE at higher temperature of 450 °C for 800 h. The alloy exhibits remarkably improved tensile and compressive yield strengths at room temperature and 200 °C and they are the results of the reinforcement of dendrite boundaries with Al₁₁RE₃ intermetallics, the fine dendritic arm spacing effect as well as the solid solution strengthening with various rare earth elements.     

Investigation of thermoelectric properties of Cu2GaxSn1 − xSe3 diamond-like compounds by hot pressing and spark plasma sintering

P-type compounds Cu₂Ga_xSn_1 ? xSe₃ (x = 0.025, 0.05, 0.075) with a diamond-like structure were consolidated using hot pressing sintering (HP) and spark plasma sintering (SPS) techniques. High-temperature thermoelectric properties as well as low-temperature Hall data are reported. Microstructural analysis shows that the distribution of Ga is homogeneous in the samples sintered by HP but inhomogeneous in the samples sintered by SPS, even with an electrically isolating and thermally conducting BN layer during the sintering. The Seebeck coefficients of the samples sintered by HP and SPS show similar dependence on the carrier concentration and are insensitive to the composition inhomogeneity. In contrast, the composition inhomogeneity results in lower carrier mobility and thus lower electrical conductivity in the samples sintered by SPS than those sintered by HP. Lattice thermal conductivity is further reduced through Ga doping; however, this effect is weakened by the inhomogeneous distribution of Ga. Due to their larger carrier mobility and lower lattice thermal conductivity, the samples sintered by HP exhibit 15–35% higher thermoelectric figure of merits (ZT) than those SPS samples with a high Ga doping level and without the coated BN layer, in which the composition homogeneity is worse. A ZT value of 0.43 is obtained for the HP Cu₂Ga_0.075Sn_0.925Se₃ sample at 700 K.     

Structural,magnetic and thermal properties of intermetallics Nd3Fe27−xCoxV2 (x = 0, 2 and 4) and their hydrides

Intermetallics of the Nd₃Fe_27?xCo_xV₂ (x = 0, 2 and 4) system with monoclinic type structure and their hydrides were prepared by arc melting and exposed to hydrogenation. The effects of Co substitution of Fe on the magnetic hyperfine fields of intermetallic compound Nd₃Fe₂₇V₂, as well as the effects of interstitial hydrogen additions on the symmetry and local magnetic properties in these systems were studied. The investigations were performed by powder X-ray diffraction, Mössbauer spectroscopy and simultaneous TGA-DSC. Both site populations and magnetic hyperfine field strength were analyzed in order to discriminate between the Co and H contributions to the local atomic environments in these systems. The values of magnetic hyperfine fields corresponding to inequivalent lattice sites were found to be enhanced after the increase in Co content and hydrogenation. Slight changes in the relative site occupancies were observed. Simultaneous TGA-DSC studies showed that the amount of hydrogen insertion decreased slightly with the increase of Co contents, while the enthalpy associated with hydrogen desorption decreased sharply under heat treatment. The Nd₃Fe_27?xCo_xV₂ (x = 0, 2 and 4) and their hydrides are not stable under treatment and two exothermic peaks are observed in the DSC curves, corresponding to the decomposition of the monoclinic phase with the precipitation of α-Fe phase.