Mechanical properties of Gd123 bulk superconductors at room temperature

In order to investigate the mechanical properties of Gd123 single-grain bulk superconductors fabricated using a modified quench and melt growth method, tensile tests in the direction parallel and perpendicular to the c-axis have been carried out at 293 K by using the small specimens cut from bulk superconductors. As for the mechanical properties perpendicular to the c-axis, there was no significant difference between those in the crystal growth direction and those perpendicular to it. While the average value of the Young’s modulus of the bulk sample with 33.0 mol%-Gd211 secondary phase particles, 118 GPa, was higher than that of the bulk sample with 28.7 mol%-Gd211, 111 GPa, the average value of the tensile strength of the former, 36 MPa, was lower than that of the latter, 40 MPa. The tensile strength and the Young’s modulus in the c-axis, 10 MPa and 37 GPa, were quite low compared with those mentioned above. Poisson’s ratio based on the transverse strain in the c-axis, 0.15, was significantly smaller than that perpendicular to it, 0.30. In the specimens with higher length, however, the difference was decreased to some extent. With regard to the anisotropy of the Poisson’s ratio, the effect of a pre-existing micro-crack opening in the c-axis direction was discussed coupled with the constraints at the interfaces between the specimen and the sample holder.     

The effect of Co electrodiffusion on the properties of YBaCuO superconductors

Diffusion over the temperature range 600-850 °C, electrodiffusion at 30 °C and effect of the Co substitution on crystalline structure and electrical characteristics of YBa²Cu³O_7-y (YBaCuO) ceramic samples have been investigated by the energy dispersive X-ray fluorescence (EDX), X-ray diffraction (XRD), resistivity-temperature and current-voltage measurements. The temperature dependence of the cobalt diffusion coefficient (600-850 °C) via the grain boundaries has been described by the relation D=5.1×10^-4exp(-1.12/kT). It is shown that the Co-doping of YBaCuO causes depression of the critical temperature and the critical current density. At the room temperature Co migrates in d.c. electric field preferentially in the form of positively charged ions with an effective charge q0.6- Electrodiffusion-stimulated orthorhombic-tetragonal transition, decrease in critical temperature and critical current density and change of the form of resistivity-temperature dependence are discovered.     

XRD spectra of new YBaCuO superconductors

XRD spectra of new YBaCuO superconductors were studied. There were 2 phases found in our samples, the superconducting phase and the non-superconducting phase. The more non-superconducting phase, the more anisotropy parameters were found. The amount of impurities have no effect on the value of c-axis which has a linear relation to the number of Cu-atoms. So the new formula of YBaCuO are the new types of superconductor in this family that have higher c-axis than the Y123.     

Fabrication and RF properties of the microwave cavity made of YBaCuO and BiPbSrCaCuO superconductors

After the discovery of new metal oxide superconductors with higher transition temperatures raised the possibility of a new class of superconducting microwave devices operating at temperatures well above liquid He, a feasibility study of the superconductor devices at r.f., microwave, and millimeter-wave frequencies, i.e., cavity resonator, transmission lines, waveguide, mirror, and antenna, was started at JAERI (Japan Atomic Energy Research Institute), Tokai in April 1987. In order to examine the feasibility of such devices and to investigate the nature of the superconductivity in these new superconductors, we have studied the microwave response of the oxide superconductors. In addition, we have also studied the fabrication and microwave properties of these devices using the new superconductors. We report here the status of the feasibility study, especially about the BSCCO and YBCO superconductor cavities, and the r.f. characterization apparatus using several cavity resonators. The cavities have potential applications for particle accelerators, resonant filters, ultrastable clocks, and so on.     

Synthesis and characterization of YBaCuO superconductors from solutions in liquid ammonia

YBa₂Cu₃O_7–x (123) superconducting powders have been advantageously prepared from liquid ammonia solutions of nitrate, acetate, and perchlorate precursors. The synthetic techniques used include solution pyrolysis, freeze drying, and chemical solidification by reaction with a Lewis acid. Metal stoichiometry was determined by gravimetric analysis and atomic absorption spectroscopy. Phase characterization was accomplished by powder X-ray diffraction which revealed at least 98% pure 123 for some samples. Resistivity and magnetic susceptibility measurements confirm the superconducting properties of the products with critical temperatures around 90 K. Finally, chemical and superconducting properties are discussed as a function of process parameters.     

On the measurement of microwave absorption of bulk YBaCuO superconductors in X-band (8–12 GHz)

Microwave absorption at the surface of highT _c YBaCUO superconducting sample has been determined in X-band by measuring VSWR. Power reflectivity >98% has been observed in the frequency range of 8·2–10·5 GHz indicating very low absorption at the surface. At some of the frequencies, however, negligible microwave loss has been observed.     

Mechanical and high speed fracture properties of polypropylene and hydrogenated poly(cyclopentadiene) blends

Mechanical tensile tests and fracture mechanics analysis at high speed were carried out on specimens of isotactic polypropylene (P P) -hydrogenated poly (cyclopentadiene) (HPCP) blends obtained under different crystallization conditions. In addition a morphological investigation of the fractured surfaces by means of scanning electron microscopy was also performed. Improved low strain properties (modulus and yield stress) were found by the addition of HPCP to PP for both quenched and highly crystallized materials. This effect is enhanced when the quenched samples undergo a further heat treatment such as annealing. The fracture toughness parameters (G _c andK _c decrease with increasing amounts of HPCP in the blend. The annealing improves the toughness of quenched samples enhancingG _c andK _c while it has no effect on samples crystallized at high temperature. All the above mechanical and fracture results were explained at the molecular level in terms of the interconnection existing in the material which depends on the crystallization conditions, annealing and blend composition.     

Mechanical and fracture properties of cellulose-fibre-reinforced epoxy laminates

Epoxy laminates reinforced with cellulose-fibre mats (CFM) have been synthesized and characterized. The influence of CFM dispersion on the mechanical and fracture properties of these laminates have been characterized in terms of elastic modulus, hardness, flexural strength, fracture toughness, indentation responses, impact-fracture, crack-growth resistance and in situ fracture. The reinforcement by the CFM resulted in a significant increase in the strain at break, indentation creep, fracture toughness and impact toughness but moderate increase in flexural strength and flexural modulus. A pronounced R-curve behaviour is exhibited by the CFM-reinforced epoxy sample, which failed in a graceful manner with slow and stable crack-growth. The micromechanisms of toughening and crack-tip failure processes are identified and discussed in the light of observed microstructures from in situ and ex situ fracture. The implications for new approaches in the ‘eco-design’ of environmentally friendly composite materials are addressed.     

Mechanical properties and fracture behavior of high-strength steels

Typical thicknesses of high-strength steels (HSS) sheets used in the car industry are inapplicable for standardized testing procedures. The aim of this study is to propose an appropriate methodology for testing and comparing of thin HSS sheets. Microstructures were observed by means of light and scanning electron microscopy. The modified Charpy impact tests and fracture toughness tests were used in order to compare the fracture properties of three different HSS sheets (Docol 1200 M, Multiphase 1200 and BTR 165). Ductile-to-brittle transition curves and tearing resistance (J − Δa) curves were measured. From the fracture toughness linked to the specimen thicknesses the value of fracture toughness K_Ic was estimated. Fractographic analysis of broken specimens has revealed that due to the fine microstructure of mixed ferrite-martensite fracture mechanism remains ductile even at low temperatures (down to −100°C). __________ Translated from Problemy Prochnosti, No. 1, pp. 155–158, January–February, 2008.     

Effect of sample density on magnetic penetration depth in YBaCuO ceramic superconductors

We have measured magnetic penetration depth(0) of high-T _c YBCO samples of different density by the cavity resonant frequency shift method at 10, 16.65, and 22.3 GHz microwave frequencies. The value of(0) at 10 GHz is found to decrease from 5850 Å to 2550 Å as the density of the sample increases from 4.4 to 5.3 g/cm³. The results of the frequency response of the penetration depth show a fairly constant value of(0) for all the three samples in the frequency range 10–22.3 GHz. The wide variation observed in the value of(0) for different density samples has been explained in terms of varying Josephson coupling strength in these ceramics.     

Granular and intergranular properties of hot pressed BSCCO (2223) superconductors

The effect of hot pressing conditions (sintering temperature and time) on the superconducting properties of (2223) Bi(Pb)SrCaCuO were investigated by transport and magnetic measurements. The advancement of the densification process leads first to an improvement of the electrical connectivity between grains (J_c transport increases) and then to a deterioration of both intragranular and intergranular properties (T_c, J_c magnetic and J_c transportdecrease) because of the induced loss of oxygen, 2212 continuous intergrain network and other defect formation.     

Metastability-induced charge and spin fluctuations in 123 type superconductors

Various defects arising from lattice mismatch and coordination incompatibility at the cation sites are known to lend the cuprates a metastable state at temperatures and pressures where they exhibit superconductivity. The present paper considers the metastability induced by coordination incompatibility at Cu(1) sites in oxygen-deficient 123 type systems and looks for their possible effects on charge and spin degrees of freedom. Depending upon the concentration of oxygen vacancies, the resulting unstable charge state at the Cu(1) sites is shown to either temporally fluctuate or spatially equilibrate, providing a mechanism for the 90 K and the 60 K plateaus, with a peak in the former observed in the YBa₂Cu₃O_7-y , samples prepared under thermodynamic equilibrium conditions.     

Mechanical properties of pure Ni and Ni-alloy substrate materials for Y-Ba-Cu-O coated superconductors

Mechanical properties of rolling-assisted, biaxially-textured substrates (RABiTS) and substrates for ion-beam assisted deposition (IBAD) coated superconductors are measured at room temperature, 76, and 4 K. Yield strength, Young’s modulus, and the proportional limit of elasticity are determined, tabulated and compared. Results obtained are intended to serve as a database of mechanical properties of substrates having the same anneal state and texture as those incorporated in the general class of RE-Ba-Cu-O coated conductor composites (RE = rare earth). The RABiTS materials measured are pure Ni, Ni-13at.%Cr, Ni-3at.%W-2at.%Fe, Ni-10at.%Cr-2at.%W, and Ni-5at.%W. The IBAD substrate materials included Inconel 625 and Hastelloy C-276. The Ni alloys are substantially stronger and show higher strains at the proportional limit than those of pure Ni. Substrates fully coated with buffer layers, ≈1 μm of Y-Ba-Cu-O, and 3-5 μm of Ag have similar mechanical properties (at 76 K) as the substrate alone. Somewhat surprisingly, plating an additional 30-40 μm of Cu stabilizer onto high-yield-strength (690 MPa) Hastelloy coated conductors ∼100 μm thick, reduces the overall yield strength of the composite structure by only about 10-12% at 76 K and 12-14% at room temperature; this indicates that the Cu layer, despite its relatively soft nature, contributes significantly to the overall strength of even high-strength coated conductors.     

Mechanical properties and fracture toughness of organo-silicate glass (OSG) low-k dielectric thin films for microelectronic applications

The integration of chemical vapor deposited organo-silicate glass (OSG) interlayer dielectrics (ILD) has challenged the IC industry to formulate new methods of metrology and characterization. The impact of nanoindentation to understand and screen for integrated circuit failure mechanisms that are mainly predicated upon OSG nano-porosity is discussed. Failure modes include poor mechanical strength, low material stiffness, and brittle fracture due to low cohesive and adhesive fracture toughness, a particular danger during chemical-mechanical polishing (CMP). By developing a methodology to predict failure modes, we are able to screen multiple candidate low-k materials. Nanoindentation measurements of elastic modulus, hardness, and fracture toughness and what they reveal about OSG porosity are discussed.     

Investigation of cube-textured Ni-7at.%W alloy substrates for YBaCuO coated superconductors

Ni-7at.%W alloys were fabricated by powder metallurgy process. After heavy cold-rolling and recrystallization annealing, sharp cube-textured Ni-7at.%W substrates were obtained. Deformation and recrystallization textures of Ni-7at.%W alloys were studied systematically. It was found that intermediate annealing during the process of cold-rolling is beneficial to the formation of a cube texture in the Ni-7at.%W substrate.