J.X Luo and Y.X. Tan (State Key Lab. for Mechanical Behavior of Materials Xi′an Jiaotong University
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Xi'an 710049
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China Manuscript received 29 September 1995)
金属学报(英文版)
The relationships between fatigue threshold △Kth and the initial yield .strength σ0 of normalized 1035 steel after various prestrain (at fist, second and third hardening stages respectively) were investigated through the analysis of theσ-εcurves and transmission electron microscope (TEM). After prestraining at first or second hardening stage, there is a marked drop in the values of △Kth and σ0. This is in correspondence with the depinning of the solute atoms from the dislocation lines in the Cottrell atmosphere.At the third hardening stage of prestrain the fatigue threshold increases rapidly and △Kth is even 1.6 times as large as the original value. This is because at this stage no dislocation-cell free areas can be found and the refinement of the dislocation cells occurs with the increase in the prestrain level.
关键词:
:deformation hardening
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E.Bayraktar
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F.Montembault
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C.Bathias
材料科学技术（英文）
The study of microstructural network and damage mechanism of polymer and rubber, although deceptively simple, involves a complex interplay between material properties and service conditions. So, the study of the texture, deformation and the failure of rubber specimens are of considerable practical interest. In fact, the occurrence of defects such as the initiation and the growth of cavitations in rubber specimens in working conditions is an important problem. These deal with the improvement of microstructure (for delaying instability) in order to obtain a higher service capacity. The scope of the present paper is, therefore, to evaluate principal mechanisms, in-situ observation of damage at mesoscopic, microscopic and macroscopic levels by using X-ray computed tomography (CT) installed in the ITMA research centre for confirming the behaviour of natural rubber (NR) and styrene butyl rubber (SBR) specimens used in automotive and aeronautical fields.
关键词:
X-ray computed tomography
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null
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null
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Applied Physics a-Materials Science & Processing
The Seebeck coefficient is a function of carrier concentration and configurational entropy. In this report, we semi-theoretically investigate the Seebeck coefficient of Ln (x) Ca(1-x) MnO(3) (Ln=Rare-earth) perovskites based on the electronic structure of the 3d orbitals of Mn ions, using the developed Heikes model, Boltzmann transport model, and diffusion model. The results show that the Seebeck coefficient of such a strongly correlated electron system in paramagnetic state is remarkably affected by site degeneracy. As temperature decreases, the evolution of the spin and orbital degrees of freedom together with the change in phonon scattering mode describes the Seebeck coefficient behavior satisfactorily. The phonon drag effect at low temperature is also discussed.
关键词:
high-temperature;thermoelectric-power;thermal-conductivity;transport-properties;single-crystals;electron;thermopower;manganites;oxide;heat
Acs Applied Materials & Interfaces
An unusual thermoelectric response was observed in n-type perovskite oxide La(1-x)Ce(x)CoO(3). Combining transport and magnetic measurements, we found that the thermoelectric response is driven by the spin-state transition of Co(3+). This transition destroys the spin blockade effect and induces an abrupt decrease of resistivity as well as an insulator metal transition. In contrast to the resistivity change, changes in thermopower and thermal conductivity are moderate. Consequently, a peak of figure of the merit ZT is present in a narrow temperature range. The room-temperature ZT approximate to 0.018 of La(0.94)Ce(0.06)CoO(3) is comparable to that of p-type Na(x)CoO(2). These observations can be helpful for the search and design of new thermoelectric materials.
关键词:
thermoelectric;electron-doping;spin-state transition;spin blockade;configuration entropy;cobalt oxides;rcoo3 r;lacoo3;fabrication;power;eu;sm;nd
Lizhi CHENG
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Wei FENG
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Xinquan DONG
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Kuichang BAI and Kaiyuan HE (Dept. of Materials Science and Engineering
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Northeastern University Shenyang 110006
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China)
材料科学技术（英文）
The formation of nonequilibrium phase by mechanical alloying (MA) of Fe and B powders in a high energy vibration ball mill has been made for Fe100-xBx system with x=15. 30, 35, 45,55 and 70. By using the X-ray diffraction, magnetic measurement and M6ssbauer spectrummethods, it was revealed that the structure of the MA product varies with milling time and B contents.
关键词:
材料科学技术（英文）
The structure, specific heat, magnetic and electrical properties of MnTe(1-x)Sb(x) (x=0, 0.1, 0.15, 0.2 and 0.25) alloys have been investigated. The MnTe(1-x)Sb(x) alloys crystallize in a hexagonal NiAs-type structure, and the impurity of MnSb phase appears when x >= 0.15. The MnTe(0.9)Sb(0.1) compound exhibits ferrimagnetic behavior with hysteresis loops even at 350 K, showing that the magnetic properties of MnTe compound are very sensitive to little compositional change. The ferromagnetism in the MnTe(1-x)Sb(x) alloys with higher Sb contents may be attributed to the impurity of MnSb phase. Energy dispersive X-ray spectroscopy analysis on the MnTe(0.9)Sb(0.1) compound indicates that Sb is very difficult to dope into the lattice of MnTe. So the anomaly of resistivity at 300 K of MnTe(0.9)Sb(0.1) and the peak of specific heat around 304 K of all the alloys are thought to be related with the antiferromagnetic interactions of MnTe-based lattice.
关键词:
Electronic transport property;Hysteresis loop;Specific heat;manganese telluride;semiconductors;ferromagnetism;scattering;exchange
D.Q.Tang
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Y. Wang
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E.Y.Jiang
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C.Zhao and F.L.Sun Department of Applied Physics
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Tianjin University
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Tianjin 300072
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China
金属学报(英文版)
CN x films were made by a facing targets sputtering ( FTS) systemon the Si(100) substrate under different N 2 partial pressure. XRD, XPS, FTIR and Raman Spectroscopy( RS) were measured to investigate the structure and the binding state of the film. The films are amorphous and the N/C increases with the N 2 partial pressure increasing and reaches 0 46 when the N 2 pressure is 100%. The N incorporated C forms N sp 2C and N sp 3C mainly and there is a small amount of C≡N.
关键词:
Physica B-Condensed Matter
The magnetic properties and magnetocaloric effect of Tb(1-x)Y(x)CoC(2) (x = 0, 0.1, 0.2, 0.3, 0.4) compounds have been investigated systematically. All the compounds undergo second-order transitions from paramagnetic to ferromagnetic states without thermal and magnetic hysteresis. With increasing Y content from 0 to 0.4, the Curie temperatures decrease nearly linearly from 28 to 18 K. The nature of the second-order phase transitions can be confirmed by Arrott plots. For Tb(0.6)Y(0.4)CoC(2) compound, the maximum value of the magnetic entropy change -Delta S(M) at 20 K is 9.35 J kg(-1) K(-1) for an external field change of 5T (5.14 J kg(-1) K(-1) for 2T). The large reversible magnetic entropy change makes Tb(0.6)Y(04)CoC(2) compound an attractive candidate for the application at hydrogen liquefaction temperature. (C) 2010 Elsevier B.V. All rights reserved.
关键词:
Curie temperature;Magnetocaloric effect;Magnetic properties;ac susceptibility
Applied Physics Letters
The effect of nonmagnetic Y partial substitution at the Dy site in Dy(1-x)Y(x)MnO(3) up to x=0.2 on magnetism, specific heat, and ferroelectricity is investigated, which resulted in a preliminary multiferroic phase diagram. It is revealed that the Y partial substitution suppresses the Dy-spin ordering point (T(Dy)) and ferroelectric ordering point (T(FE)) but enhances the Mn-spin ordering point (T(N)). The interaction between the spins of Dy and Mn is remarkably affected by Y substitution. The measured electrical polarization depends on the Y substitution in a complex way because the ferroelectricity is sensitive to the interaction between the spins of Dy and Mn. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3536506]
关键词:
ferroelectricity;polarization
Journal of Physical Chemistry C
We report the electrical, thermal, magnetic, and thermoelectric properties of Y-doped Ca(3)Co(4)O(9) from 300 down to 5 K. The results indicate that with Y doping, the increase of resistivity originates from the decreases of carrier concentration and mobility, while the increase of Seebeck coefficient is caused by the reduction of carrier concentration together with the enhanced electronic correlation. Point-defect scattering, is the dominant thermal transport mechanism in this system. Due to the considerable difference in mass between Y(3+) and Ca(2+), thermal conductivity is observably suppressed by doping. The substitution of Y also disturbs the interlayer ferrimagnetic coupling. The ground state of this System converts front ferrimagnetism to paramagnetism gradually. The alteration of transport properties of Ca(3-x)Y(x)Co(4)O(9) reveals two Crossovers: the transition from Fermi-liquid-like metal to thermally activated semiconductor occuring at x approximate to 0.25, and the transition from thermally activated semiconductor to two-dimensional variable range hopping semiconductor occurring at x approximate to 0.5. The optimal thermoelectric response In Ca(3-x)Y(x)Co(4)O(9) is found to exist only at the critical state after which the doping-induced metal-insulator transition takes place. Oil the basis of these experimental results, a possible phase diagram for Ca(3-x)Y(x)Co(4)O(9) is proposed.
关键词:
temperature thermoelectric properties;giant magnetoresistance;solid-solutions;conductivity;electron;system;ca3co4o9+delta;thermopower;crystals;behavior
