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1.
Magnetic memory testing (MMT) method is a novel non-destructive testing technique due to its unique advantages of stress concentration identification and early damage detection for ferromagnetic materials. However, a thorough understanding of the impact of exciting magnetic source and cyclic stress on the residual magnetic field variation has not been clearly addressed. The surface magnetic memory signal Hp(y) induced by applied magnetic field and cyclic tensile stress was measured throughout the fatigue process. The correlation of Hp(y) and its gradient K changes with loading cycles and applied magnetic field intensity H reported. The results show that applied magnetic field can only change the magnitude of MMT signal instead of changing the Hp(y) curve׳s profile. The Hp(y) value increases with the increase of the H, and the K value is approximately linear to the H. The maximum gradient Kmax indicating the degree of stress concentration increases with the increase of either stress cycles or H. The phenomenon was also discussed from the view of the magnetic dipole in a ferromagnet. 相似文献
2.
Variation of stress-induced magnetic signals during tensile testing of ferromagnetic steels 总被引:1,自引:0,他引:1
Stress alone applied to ferromagnetic materials can induce the generation of weak magnetic signals on their surfaces, which can be potentially used to estimate the degree of damage of ferromagnetic components. In this paper, the normal component of stress-induced magnetic field, Hp(y), was measured during tensile tests on the surfaces of sheet specimens of three ferromagnetic materials. It has been concluded that Hp(y) depends on the applied stress and will present different characteristics on the elastic and plastic deformation stages, respectively. The phenomenon of sharp changes in magnetic signals occurring at the instant of fracture was also discussed from the view of the interaction energy in a ferromagnet. 相似文献
3.
Lihong Dong Binshi Xu Shiyun Dong Li Song Qunzhi Chen Dan Wang 《NDT & E International》2009,42(4):323-327
Measuring spontaneous stray field signals provides a promising tool to analyze the stress in ferromagnetic materials. However, strong initial stray field signals on the surface of ferromagnetic materials originating from various manufacturing processes can disturb stress-induced stray field signals. Consequently, it is necessary to conduct a study that will clarify the stress dependence of spontaneous stray field signals by eliminating initial random signals. In the present work, the focus is placed on sheet specimens that have a clean initial magnetic state by means of vacuum heat treatment. Measurements of the normal component Hp(y) signals of stray field were performed during the whole tensile test. The results showed that the stress-induced Hp(y) signal curve had good linearity after loading, i.e., the slope coefficient Ks increased continuously in the elastic deformation stage but decreased slightly during the plastic deformation stage. This phenomenon was discussed and explained from both the stress-induced effective magnetic field and residual compressive stress viewpoints. 相似文献
4.
基于压磁理论,探讨激光熔覆层应力的磁记忆评价机理.基于激光熔覆层SEM观察对磁记忆法向分量Hp(y)信号进行分析.结果表明,随应力增大,激光熔覆层磁记忆法向分量Hp(y)曲线以过零点为中心呈逆时针转动,磁畴由无序向有序转变使得Hp(y)曲线斜率逐渐变大,当应力达到520 MPa(小于试样屈服强度)时,再随应力的增大,Hp(y)曲线斜率逐渐变小.分析认为,激光熔覆层的快速凝固各向异性组织及其中界面导致激光熔覆层呈不均匀塑性变形过程是引起上述结果的主要原因,也是应力小于试样屈服极限时,Hp(y)曲线斜率随应力增大呈减小趋势变化的原因之一. 相似文献
5.
N. Sheloudko C. Sarafidis M. Gjoka K.G. Efthimiadis O. Kalogirou 《Journal of Alloys and Compounds》2009,482(1-2):19-22
Starting with a Ho3(Fe1−xCox)29−yCry, (x,y) = (0.6,4.5) and (0.8,5.5) nominal stoichiometry, a disordered variant of the hexagonal 2:17 phase (Th2Ni17-type, S.G. P63/mmc) occurs, since both the monoclinic 3:29 and the transition-metal-rich disordered Th2Ni17-type hexagonal compounds have the same rare earth to transition metal ratio, 1:9.7. The magnetic properties and the magnetocrystalline anisotropy of these compounds have been investigated. The anisotropy constant, K's, and the anisotropy field, μ0HA, values have been deduced from the magnetization curves measured on powder samples magnetically aligned in a rotating magnetic field. The compound with (x,y) = (0.8,5.5) shows a compensation point at about 55 K. The magnetic anisotropy of both compounds is that of easy-plane from room temperature to low temperatures down to 5 K. 相似文献
6.
The transverse magnetoresistance of α-(BEDT-TTF)2KHg(SCN)4 was investigated with the magnetic field rotated within a conducting ac-plane. It was found that the magnetic-field-orientation dependence of the magnetoresistance in the weak-field limit, ΔR(B,θ), has the form ΔR(B,θ) = B2(psin2(θ − θmin) + qcos2(θ − θmin), where θ is the angle betweeen a-axis and magnetic field direction and (p, q, θmin) are temperature-dependent parameters. By examining the results based on the classical theory of magnetoresistance, it was concluded that the electrical anisotropy within be-plane is 3.5 4.5 and 2.5 3.0 above and below the phase transition at 10 K, respectively. 相似文献
7.
The ternary InSb–NiSb–Sb system has been studied by X-ray diffraction and by potentiometry. The electromotive forces (EMF) have been measured in the temperature range 640<T/K<860 by using the following galvanic cell:with x (0.075<x<0.498) and y (0<y<0.359). The investigated samples are located on the following lines of the Gibbs triangle: InSb–Ni0.33Sb0.66, InSb–Ni0.48Sb0.52, InSb–NiSb, Sb–(InSb)0.75(NiSb)0.25, Sb–(InSb)0. 5(NiSb)0.5, Sb–(InSb)0.25(NiSb)0.75. From these measurements, the values of the partial molar thermodynamic functions (Δμ°m,In, ΔH°m,In, ΔS°m,In) (data at reference pressure p0=105 Pa), for the liquid InSb alloy, for the three solid heterogeneous regions InSb–NiSb2–Sb, InSb–NiSb1±δ?–NiSb2, InSb–NiSb1±δ, for six ternary liquid–solid alloys, have been calculated. 相似文献
8.
W. Cheikh-Rouhou Koubaa M. Koubaa A. Cheikhrouhou 《Journal of Alloys and Compounds》2009,470(1-2):42-46
We investigate the effect of potassium doping on the structural, magnetic and magnetocaloric properties of La0.7Sr0.3−xKxMnO3 (x = 0.05, 0.1, 0.15 and 0.2) powder samples. Our polycrystalline compounds were synthesized using the solid-state reaction at high temperature. X-ray diffraction characterizations showed that all our studied samples crystallize in the distorted rhombohedral system with space group. With increasing potassium content, the unit cell volume exhibits a broad maximum around x = 0.15. Magnetization measurements versus temperature showed that all our samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature TC is found to decrease from 365 K for x = 0 to 328 K for x = 0.2 as well as the saturated magnetization Msp which shifts from 3.68 μB/Mn for x = 0 to 3.05 μB/Mn for x = 0.2. The critical exponent γ defined as Msp (T) = Msp(0)[1−(T/TC)]γ is found to remain almost constant and equal to 0.33 for all our samples. The maximum of magnetic entropy changes |ΔSmax| of La0.7Sr0.3−xKxMnO3 for x = 0.05 and 0.15 is found to be respectively, 1.37 and 1.2 J kg−1 K−1 under a magnetic field change of 1 T. 相似文献
9.
The Y1−xYbx/2Gdx/2Ba2Cu3O7−y superconducting samples for x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 were prepared by using the solid-state reaction technique. Resistivity measurements of the samples were performed in QD–PPMS system under different magnetic fields up to 5 T in zero fields cooling regime. Using the resistivity data, the upper critical magnetic field Hc2(0) at T = 0 K for 50% of Rn was calculated by the extrapolation Hc2(T) to the temperature T = 0 K. The coherence length in T = 0 K were calculated from Hc2(0) and the effects of x in the composition on both the coherence length and the upper critical magnetic field were examined. The results showed that Hc2(0) varied from 84.05 to 122.26 T with the content x. The upper critical magnetic field in the temperature T = 0 K slightly decreased with increasing the content x. Using the content x, the upper critical magnetic field can be controlled and this can be used in the superconductivity applications. 相似文献
10.
Rong-Tsong Lee Yih-Chyun Hwang Yuang-Cherng Chiou 《International Journal of Machine Tools and Manufacture》2006,46(10):1146-1156
A general closed-form analytical solution is derived for the lapping tracks with its kinematics for the concentric V-groove lapping system. Based on the kinematics, the theoretical prediction in the prediction of the ball-spin angle β is in very good agreement with the experimental results from the observation of the contact track, where a small slip ratio occurs at the contact points. The lapping tracks on the ball surface for the three contact points are fixed circles, and their lengths of the lapping tracks are linearly proportional to |sin(θ1+β)|, |sin(θ2+β)|, and |cos β|, respectively. To understand the generation mechanism of spherical surface, the ball is enforced to rotate a certain degree of δ with respect to its previous orientation when it enters the lap again. Results show that the lapped area ratio, Lr, is significantly influenced by the angular speed ratio, wb/Ωb, and δ. When the angular speed ratio is integer and δ is small enough or randomized, the lapped area ratios at the contact points of A, B, and C are linearly proportional to [sin θ+sin(θ+2β)], [sin θ+sin(θ−2β)], and (1+cos 2β), respectively. In practice, if the orientation is randomized as the ball enters the lap again, then the distribution of the lapping tracks are dense after many cycles, and the larger the lapping length in each cycle, the smaller is the number of cycles required to achieve the maximum lapped area ratio. In the geometry design of ball lapping, the V-groove half-angle should be larger than 45°, but to prevent the splash of abrasives, it should be less than 75°. 相似文献
11.
The ternary system (1 − x − y)Bi0.5Na0.5TiO3–xBi0.5K0.5TiO3–yBi0.5Li0.5TiO3 (abbreviated to BNKLT-x/y) was synthesized by conventional oxide-mixed method. The phase structure, microstructure, and dielectric, ferroelectric and piezoelectric properties of the ceramics were investigated. The X-ray diffraction patterns showed that pure perovskite phase with rhombohedral structure can be obtained in all the ceramics. The grain size varied with x and y. The temperature dependence of dielectric constant and dielectric loss revealed there were two phase transitions which were from ferroelectric (tetragonal) to anti-ferroelectric (rhombohedral) and anti-ferroelectric to paraelectric (cubic). Either increasing x or y content can make Tm (the temperature at which dielectric constant r reaches the maximum) increase. With the addition of Bi0.5K0.5TiO3, the remanent polarization Pr increased but the coercive field Ec decreased. With the addition of Bi0.5Li0.5TiO3, Pr increased obviously and Ec increased slightly. Due to the stronger ferroelectricity by modifying Bi0.5K0.5TiO3 and Bi0.5Li0.5TiO3, the piezoelectric properties were enhanced at x = 0.22 and y = 0.10, which were as follows: Pr = 31.92 μC/cm2, Ec = 32.40 kV/cm, r = 1118, tan δ = 0.041, d33 = 203 pC/N and Kp = 0.31. The results show that the BNKLT-x/y ceramics are promising candidates for the lead-free materials. 相似文献
12.
L. Havela A.V. Andreev A.P. Gonalves J. ebek V. Sechovský Y.F. Popov 《Journal of Alloys and Compounds》2008,460(1-2):83-89
The intermetallic compound UGa1.85Zr0.15 does not crystallize in the AlB2 structure shared by UGa2 and UZr2. Instead, it forms in the same orthorhombic structure as U3Ga5 (Pu3Pd5 type), but the somewhat smaller lattice parameters reduce the unit cell volume by 2.1% with respect to U3Ga5. Basic magnetic properties, namely the ferromagnetic ground state below TC = 23 K, are similar to U3Ga5. A more detail study of magnetic properties reveals interesting metamagnetic behavior with a critical field of 2–3 T, which increases with increasing temperature. The high γ-value of 110 mJ mol−1 K−2 points to a narrow 5f band at Fermi level. 相似文献
13.
A fracture mechanics-based novel approach, i.e. circumferential notch tensile (CNT) testing has been employed for determination of threshold stress intensity factor for susceptibility of engineering materials to stress corrosion cracking (KISCC) using small specimens. Using CNT technique, KISCC of a carbon steel at an open circuit potential (Ecorr) in 500 g L−1 NaOH at 100 °C was determined to be 42.9 MPa m1/2. In order to establish the application of the CNT technique in understanding the mechanistic aspects of caustic cracking as well as for developing guidelines for mitigation, tests have also been performed under the imposed electrochemical potentials. An imposed potential in the active–passive potential regime (Ea–p) caused an extremely rapid failure (than observed at Ecorr) whereas, at an imposed potential in the passive region (Ep), the specimen did not fail even after relatively very long exposure time. The fractography of the CNT specimens tested at Ecorr and Ea–p presented evidence of SCC. The study has established the use of experimental CNT testing as a simple, relatively fast and cost-advantageous approach for generating the KISCC data, which are also consistent with the electrochemical mechanism for caustic cracking. 相似文献
14.
S. C. Parida Ziley Singh Smruti Dash R. Prasad V. Venugopal 《Journal of Alloys and Compounds》1998,280(1-2)
The enthalpy increments and the standard molar Gibbs energies in the formation of LaFeO3(s) have been measured using a high-temperature Calvet micro-calorimeter and a solid oxide galvanic cell, respectively. The corresponding expression for enthalpy increments is given as:The heat capacity, the first differential of H°(T)−H°(298.15 K) with respect to temperature, is given as:From the measured e.m.f. of the cell, (−)Pt/(LaFeO3(s)+La2O3(s)+Fe(s))//CSZ//(Ni(s)+NiO(s))/Pt(+), and the relevant ΔfGm°(T) values from the literature, the ΔfGm°(LaFeO3, s, T) was calculated, and is given as:The calculated ΔfHm°(LaFeO3, s, 298.15 K) and S°(298.15 K) values obtained using the second law method are −1334.7 kJ mol−1 and 128.9 J K−1 mol−1, respectively. 相似文献
H°(T)−H°(298.15 K)(J mol−1)(±1.2%)=−36887.27+103.53 T(K)+25.997×10−3T2(K)+11.055×105/T(K).
Cp,m°(T)(JK−1mol−1)=103.53+51.994×10−3T(K)−11.055×105/T2(K).
ΔfGm°(LaFeO3, s, T)(kJmol−1)(±0.72)=−1319.2+0.2317T(K).
15.
Assume that the intergranular phase (IP) existing between adjacent grains is a weak magnetic phase, and could weaken or interrupt the intergrain exchange-coupling interaction (IECI). Using our proposed cubic-grain anisotropy model, we investigate the effects of IP's thickness d, and its anisotropy constant K1(0) on the coercivity of nanocrystalline Nd–Fe–B magnet. Calculation results indicate that the coercivity increases with increasing d, but decreases with increasing K1(0). When d = 1.2 nm and K1(0) = 0.5K1 (K1 is the common anisotropy constant of the bulk Nd–Fe–B material), our calculated results are consistent with available experimental data. 相似文献
16.
N. G. Bebenin R. I. Zainullina N. S. Bannikova L. V. Elokhina V. V. Ustinov Ya. M. Mukovskii 《The Physics of Metals and Metallography》2009,108(3):232-236
The dependence of the resistance ρ of the La0.7Ca0.3MnO3 single crystal on the temperature (in a range of 77 < T < 410 K) and magnetic field H is studied. The dependence of the magnetoresistance Δρ/ρ of the ferromagnetic phase on the field is shown to be determined
by the competition of two mechanisms. In low magnetic fields, the magnetoresistance is positive Δρ/ρ > 0 and is determined
by changes in the resistance with changing magnetization orientation with respect to the crystallographic axes; in high magnetic
fields, the magnetoresistance is negative Δρ/ρ < 0, since it is the suppression of spin fluctuations in the magnetic field
that plays the principal role. The phase transition from the ferromagnetic to paramagnetic state is a first-order transition
close to the second-order one. In the transition range, the magnetoresistance is determined by the resistivity in the zero
field ρ(T) and by the shift of the transition temperature T
C(H) in the magnetic field. In the paramagnetic state, the resistivity ρ(T) has an activation character; similarly to the magnetoresistance of other lanthanum manganites, the magnetoresistance of
this single crystal is controlled by a change in the activation energy in the magnetic field. 相似文献
17.
Shun Li Shuxin Bai Hong Zhang Ke Chen Jiayu Xiao 《Journal of Alloys and Compounds》2009,470(1-2):141-144
The effects of Nb and C additions on the crystallization behavior, microstructure and magnetic properties of B-rich Nd9.4Fe79.6−xNbxB11−yCy (x = 0, 2, and 4; y = 0, 0.5, and 1.5) alloy ribbons have been investigated. The results show that Nb and C additions change the crystallization behavior of Nd9.4Fe79.6B11, avoid the formation of metastable Nd2Fe23B3 phase, leading to the simultaneously precipitation of α-Fe and Nd2Fe14B phases. The results also show that Nb and C additions suppress the formation and growth of the soft α-Fe phases, leading to the presence of a large amount of Nd2Fe14B phases. Nb and C additions also refine the structure, and thus increase the exchange coupling interaction between the soft and hard phases. Excellent magnetic properties of Br = 0.85 T, iHc = 1106 kA/m, and (BH)max = 117 kJ/m3 have been achieved in Nd9.4Fe75.6Nb4B10.5C0.5 alloy ribbons. 相似文献
18.
Hua-Qiang Wu Dong-Mei Xu Qiang Wang Qian-Yi Wang Gui-Qin Su Xian-Wen Wei 《Journal of Alloys and Compounds》2008,463(1-2):78-83
FexCoyNi100−x−y alloy nanoparticles with controllable compositions attached on the surface of carbon nanotubes (CNTs) were synthesized using an easy two-step route including adsorption and reduction processes. The nanocomposites have been characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-disperse X-ray spectroscopy (EDS) and vibrating sample magnetometer (VSM). The effect of the alloy composition on microstructure and magnetic properties of ternary FeCoNi alloys attached on carbon nanotubes have been studied. During the nominal composition range (x = 21, 24, 33, 37, 46 and y = 60, 46, 48, 48, 35), FexCoyNi100−x−y alloy nanoparticles attached on CNTs are quasi-spherical, fcc–bcc dual phase, and the coercivity (Hc) and saturation magnetization (Ms) vary with the alloy composition. The Hc of FexCoyNi100−x−y alloy nanoparticles attached on CNTs decreases and Ms increases with increasing Fe content. These demonstrate that the two-step route is promising for fabricating alloy nanoparticles attached on CNTs for magnetic storage and ultra high-density magnetic recording applications. 相似文献
19.
Shaowei Bie Jianjun Jiang Gang Du Qiang Ma Lin Yuan Yongjiang Di Zekun Feng Huahui He 《Journal of Alloys and Compounds》2008,463(1-2):471-474
CoNbZr films for an adjustable magnetic anisotropy field Hk by doping with rare-earth of different atomic ratio Tb element were obtained in this work. The effect of Tb addition ranged from 0 to 4 at.% on the magnetic properties of the amorphous CoNbZr films was further investigated. The results show that the magnetic anisotropy field Hk increases sharply with the addition of Tb while the coercivity Hch along the hard axis and Hce along the easy axis change slightly with increasing Tb content in the films. As a consequence, CoNbZr film doped with 2 at.% of Tb exhibits excellent soft magnetic properties with a saturation magnetization 4πMs of 8.9 kG, a hard axis coercivity Hch of 1.79 Oe, a easy axis coercivity Hce of 1.4 Oe and a magnetic anisotropy field Hk of 87 Oe. The measured ferromagnetic resonance frequency fFMR of this film is 2.30 GHz. The real permeability μ′ is about 100, which is maintained up to 2 GHz. In addition, there is a broad band of the imaginary permeability μ″ over a large frequency band, indicating high losses. Therefore, Tb doped CoNbZr film is an excellent candidate for high frequency applications such as electromagnetic interference suppressors. 相似文献
20.
《Intermetallics》2014
The specific heat Cp(T) of the Mn5Ge3 ferromagnet has been studied in a wide temperature range of 2–400 K. The ferromagnetic ordering has been confirmed at TC = 297.4 K, however the behaviour of Cp(T,H) in small magnetic fields suggests a presence of a weak antiparallel component in the magnetic structure. The combination of the Cp(T,H) and magnetization M(T,H) measurements enabled the determination of not only the isothermal magnetic entropy change ΔSM but the adiabatic temperature change ΔTad as well. It has been also found that the mechanical milling process leads only to a moderate drop of the magnetocaloric effect. The reduction of the grain size by 50% decreases the relative cooling power by 28%. 相似文献