Resistivity and Susceptibility of Y-Ba-Cu and Bi-Sr-Ca-Cu Oxides

The resistivity and magnetic susceptibility ofthe quenched samples for the Y-Ba-Cu oxideswere measured at room temperature.Themeasurement for the temperature dependence of theamorphous Bi-Sr-Ca-Cu oxides with differentheat treatment temperature was made.Theresistivity and the parameters C in the formulax=X_0+C/(T-0)of the quenched samples forY-Ba-Cu oxides decreased with lowering quenchtemperature,and their susceptibility did not varymonotonously with quench temperature.The tem-perature dependence of the amorphousBi-Sr-Ca-Cu oxides gradually deviates fromCurie-Weiss law with increasing heat treatmenttemperature.The local magnetic moments forY-Ba-Cu and amorphous Bi-Sr-Ca-Cu oxidesgradually decrease with decreasing quench tempera-ture or increasing heat treatment temperature.     

Strength of Materials and Structures

Book reviewAll engineering structures designed according to modern principles have to be strong and sufficiently rigid. Scientists and engineers have long recognized the importance of the strength ofmaterials and structures, and dedicated much their efforts to bothfundamental and industrial research into the theory for vast engineering materials and various structures. A lot of engineers needto be familiar with the fundamental principles of strength in materials and structures in order to desi…     

Wide Scale Characterization and Modeling of the Vibration and Damping Behavior of CFRP-Elastomer-Metal Laminates—Comparison and Discussion of Different Test Setups

Applied Composite Materials - The investigated hybrid carbon fiber reinforced plastics-elastomer-metal laminates (HyCEML) offer the potential of tailored structural materials with adaptable damping...     

Magnetothermal Analysis of Nanocrystallization of Amorphous and Relaxations of Nanocrystalline Materials

For a few years it has been realized that nanocrystalline phases can be formed during crystallization of amorphous alloys annealed isothermally below the crystallization temperature of usual heating experiments. Data of this transformation monitored by the measurement of magnetic susceptibility are presented. A method using a magnetic balance with electronic stabilisation and combined computer facilities is applied. Constant heating and cooling rates as well as isothermal heat treatments are used. Magnetic measurements are able to detect the onset of the transformation of amorphous Ni-P alloys much earlier than was possible with differential scanning calorimetry. The transformation kinetics can be analyzed by means of the Avrami plot based on the Johnson-Mehl-Avrami equation.The kinetics of solid state reactions in the nanostructured material can be investigated similarly. Formation of a Ni-phase in a nanostructured Hf-Ni alloy could be detected in a very early stage, where calorimetric methods are not sensitive. Segregation phenomena could be detected from the experiments even after long time. The sensitivity of the applied method is not dependent on the heating rate as the sensitivity of scanning calorimetry is     

Structural, Electronic and Magnetic Properties of Nanolayer and?Bulk of MnCo2Si and MnFeCoSi Compounds

In the present work we have investigated the structural, electronic and magnetic properties of MnCo₂Si and MnFeCoSi in bulk and nanolayer using density functional theory. The total energies as a function of volume are calculated and thereby the bulk modulus and their pressure derivatives are determined. The effect of atoms at the surface of these nanolayers has been analyzed using the calculated total and partial electron density of states in its ferromagnetic phase. The spin-polarized density of states show that both bulk MnCo₂Si and MnFeCoSi present a half-metallicity, which is lost at their nanolayer surfaces. Furthermore, the effects of pressure on the magnetic moment of these compounds in its bulk form are investigated.     

Effects of phosphorus on creep behaviour of nickel and Ni–20Cr and on creep and strength of Nimonic 80A

Abstract

The influence of P on the creep behaviour of Ni, Ni–20Cr (wt-%), and Nimonic 80A was investigated by carrying out creep tests under various loads and at different temperatures. After creep fracture the samples were investigated using optical, scanning electron, and transmission electron microscopy. The grain boundary segregation was examined using Auger electron spectroscopy (AES). It was found that P segregates to the grain boundaries in all the materials investigated. The creep rate of Ni–20Cr and Nimonic 80A is decreased by the addition of P. Grain boundary segregation of P and its influence on strength was also investigated using AES for specimens aged between 600 and 700°C after fracture by a tensile test inside an ultrahigh vacuum chamber. Maxima of tensile strength are observed to be time dependent as a result of carbide precipitation, which is affected by the P segregation.

MST/1679     

Department of Metallurgy and Materials Engineering of Chongqing University

Chongqing University is located inChongqing City,Sichuan Province.Foundedoriginally in 1929,the university has sincethen greatly expanded in its scope ofeducation and organization.Now it becomesone of China's key universities of scienceand engineering with 18 departments and38 specialities.In addition it has 20 researchinstitutes and about one hundred laboratories.The department of metallurgy and ma-terials engineering of Chongqing University     

Computational Study of Structure and Thermochemistry of Some Endo‐ and Exohedral Fullerene Derivatives

Abstract

DFT calculations were applied to the problem of fullerene isomerism. Two classes of thermally stable fullerene derivatives are considered: endohedral metallofullerenes, which in some cases reveal carbon cage topology different from that observed in the empty fullerenes of the same size, and fullerene fluorides, which have uniquely rich number of theoretically possible isomers.     

The Establishment of National TC of Certification and Accreditation

National standardization tech-nical committee of certifi-cation and accreditation was established on Jan 15th, 2003 in the 1st Certification and Ac-creditation Committee Member Conference held by Certification and Accreditation Administration of P.R.C.. Wang Fengqing, director of Certification and Accreditation Administration of P.R.C. (CNCA), assumed the director of the com-mittee. The committee members include both individuals and units such as Legislative Affairs Office of the …     

Analysis of interactions between damage and basic creep of HPC and HPFRC heated between 20 and 80 °C

The present study concerns the uniaxial compressive creep of High Performance Concrete (HPC) at moderate temperatures, 20–80 °C. The study was conducted on four formulations of HPC including two fibrous concretes envisioned for future storage structures of Intermediate Level Long-Life Nuclear Wastes. These wastes are exothermic and lead to maximal temperatures in the field ranging from 50 to 70 °C (Andra, Référentiel des matériaux de stockage de déchets à haute activité et à vie longue, 2005). Here, we investigate the basic creep under uniaxial compression at 50 and 80 °C and compare it to that obtained on the same HPC at 20 °C. The objective of this research is to contribute to a better understanding of the phenomenon of interaction between damage and basic creep of HPC at moderate temperature, especially with a view to its integration in Thermo-Hydro-Mechanical models dealing with the design of special structures (massive structures, specific serviceability conditions in nuclear or hydroelectric power plants, etc.). This test campaign allowed us to assess the effect of temperature on the magnitude of basic creep of HPC, and also the impact of various temperature and mechanical loading conditions on the Young’s modulus of HPC. Heating to 80 °C damages HPC (instantaneous Young’s modulus decrease) and thereby increases the creep capacity, showing a relation between damage and creep amplitude. Moreover, this study gives global activation energy of basic creep of HPC that should be useful for practitioners dealing with concrete structures sensitive to delayed strains and subjected to moderate temperature.     

Influence of retrogression and reaging on microstructure and properties of 8090 Al–Li alloy

Abstract

An investigation was made into the influence of a retrogression and reaging treatment on the microstructure, tensile properties, and stress corrosion cracking resistance of 8090 Al–Li alloy. The results show that retrogression of the material at 230°C for 40 min or 325°C for 1·5 min, and then reaging to the peak aged condition, can result in an improved combination of tensile strength and stress corrosion cracking resistance. Through retrogression and reaging treatment, the alloy almost achieves the strength of the peak aged state and the stress corrosion cracking resistance of the overaged state. Transmission electron microscopy indicates that the δ′ phase dissolves during retrogression and reprecipitates during reaging, thus increasing the strength. The T₂ phase precipitates and grows during both retrogression and reaging, which results in the increase of stress corrosion cracking resistance.

MST/1670     

Effect of amount and atomic ratio of dual modifiers Ca and Mg on phase formation and mechanical properties of Ca,Mg-α-Sialons

Multi-cation -Sialons ceramics containing calcium and magnesium for the compositions ((Ca,Mg)_xSi_{12 – 3x}Al_3xO_xN_{16 – x}), where x equals 0.6 and 1.0 with the different atomic ratios of Ca to Mg, were fabricated by hot-pressing. An exploration for Ca,Mg--Sialon involving phase compositions, cell dimensions, microstructure and mechanical properties were carried out in the present work.     

Structure and Deformation of Intermetallic Beryllides

Intermetallic beryllides are potential light-weight, high-temperature structural materials. In this paper. the processing techniques, microstructure. deformation, and oxidation properties of intermetallic beryllides are described. In addition to nickel beryllides (NiBe). which is treated as a model system.other high beryllium-containing refractory beryllides, such as Nb2 Be17. VBe12. are also studied.The room temperature deformation and high-temperature creep properties of these beryllides are repor4ed. At room temperature. NiBe exhibits certain tensile ductility (~ 1 .3%). but all other beryllides are essentially brittle. Nonetheless, these beryllides become ductile at temperatures above approximately 1000℃. Their creep properties are presented. The creep properties are compared with those of intermetallic aluminides. Also. a comparison is made between the ductile-to-brittle transition behaviour of intermetallic beryllides and that of aluminides. Although beryllides are generally oxidation resistant at high temperatures, some beryllides, e.g., ZrBe13, suffer the pest reaction during oxidation at intermediate tem peratures. The pest mechanisms are proposed     

University of Science and Technology Beijing

University of Science and TechnologyBeijing (former Beijing University of Ironand Steel Technology)--one of the nationalleading universities, featuring in metallurgyand materials, is a polytechnic, takingengineering as main course and combiningtogether science, engineering, management     

Effects of microadditions of vanadium and boron on age hardening and mechanical properties of Al–Li alloy 8090

Abstract

The effects of micro additions of vanadium and boron on the age hardening, microstructure, mechanical properties, deformation, and fracture behaviour of Al–Li alloy 8090 have been investigated. The addition of 0·6% V to 8090 alloy increases the peak hardness by 13%, the yield strength by 23%, and the ductility by 85% when optimally aged (190°C for 22·5 h). The enhancement of these properties is attributed to the refinement of S′ and δ′ precipitates and the promotion of extensive cross-slip during deformation of the vanadium containing alloys. The same amount of vanadium reduces the impact toughness of 8090 by 50%, which is attributed to the presence of coarse particles of primary Al₁₁V precipitate. Increasing the cooling rate during solidification, or adding 0·1%B, restores and slightly increases the impact toughness of the vanadium containing alloy. The effect of cooling rate is related to the amount and size of Al₁₁V precipitates, which decrease with increasing cooling rate. The addition of boron appears to modify the morphology of the Al₁₁V precipitate.

MST/1584     

Complex impedance and admittance of yttria-stabilized zirconia andβ-alumina

Reported complex impedance and admittance data for yttria-stabilized zirconia and-alumina have been studied in the light of information obtained from an ion-conducting glass. From the analysis it was found that the a.c. response of those crystalline electrolytes resembles that of a glass; namely, apart from complications such as grain boundaries and second phases, the universal nature which prevails in solid electrolytes is a change of an equivalent circuit from a parallelRC to a seriesRC circuit with increasing temperatures as a result of formation and development of the charge-carrier-depleted region near the electrode as ionic conduction proceeds.