Influence of High Pressure and Temperature on the Structure and Properties of the WC–6Co Hard Alloy

The results are presented of the barothermal treatment studies of a WC–6Co hard alloy at high pressure (7 GPa). It is shown that such a treatment of hard alloy leads to the deterioration of the basic physico-mechanical characteristics, specifically the strength at the contact, and the coercive force, which is stipulated by the increase of the defects amount in the structure of the carbide phase of the hard alloy.     

Effect of Compaction Pressure on Structural and Superconducting Properties of Bi-2223 Superconductors

In this work, effects of compaction pressure on the structural and superconducting properties of BSCCO ceramic superconductors were investigated. The study was carried out on two systems which were, System I: Bi_1.7Pb_0.3Sr₂Ca₂Cu₃O _y and System II: Bi_1.6Pb_0.3Ag_0.1Sr₂Ca₂Cu₃O _y , respectively. Ceramic powders were prepared by conventional solid-state reaction method and sintered at 850°C after compaction at five different pressures in the 150–750 MPa range. Critical temperatures of samples were determined by resistivity-temperature determinations made by four-point probe method in liquid nitrogen conditions. XRD analysis was conducted by powder X-ray diffraction method. Morphology of the grains present in the samples were determined by using scanning electron microscope (SEM) photographs at 2 K× and 2.5 K× magnifications for System I and System II, respectively. Sintered densities of the superconducting ceramics were measured by Archimedes water displacement method and unit cell parameters were additionally obtained from XRD data. T _c values for System I was determined to be in the 109–115 K with sample D having the highest T _c of 115 K while T _c varied in the 104–109 K range and sample B had the highest T _c value of 109 K for System II. The transition width, which is a sign of the purity of the samples, was determined to be narrow for both systems. The data obtained from X-ray diffraction measurements have shown that 2223 high-T _c phase was dominant in both systems. The determination of the optimum pellet compaction pressure for BSCCO ceramic superconductors was the main purpose of this work. The results of this work indicated that compaction at around 450 MPa improves the superconducting and structural properties of the BSCCO ceramic superconductors.     

Effect of Melt Processing Programme on Microstructure and Properties of YBCO Thick Films

The screen printing technique was used in the fabrication of YBa₂Cu₃O_7−σ (YBCO) superconducting thick films on yttria stabilised zirconia (YSZ) substrates. Different slow cooling rates were used in the preparation of YBCO thick films after fast cooling from the melt processing temperature. The effects of the melt processing programme on texturing, microstructure and superconducting properties of the melt processed YBCO films were studied. Slow cooling rates between 1005 and 990 °C were effective in increasing the interaction of viscous molten with reduced film/substrate, and hence a relatively large grain size has been obtained. Moreover, different c-axis texturing ratios and grain morphologies were observed.     

Effect of Firing Temperature on the Structure and Properties of YBa2Cu3O7−x Films by TFA-MOD Method

YBa₂Cu₃O_7−x (YBCO) films were fabricated on LaAlO₃ (LAO) substrate under various firing temperatures (760–870 °C) in the crystallization process by metalorganic deposition (MOD) method using trifluoroacetates. The effect of firing temperature on the structure and properties of YBCO films was systematically investigated. According to the XRD and SEM images, the films fired at low temperature (760–800 °C) showed poor electrical performance due to rough surfaces and impurity phases. However, the films fired at 850 °C showed the highest critical temperature of 90 K and the highest J _c of 3.1 MA/cm² which attribute to the formation of a purer YBCO phase, fewer pores, and stronger biaxial texture.     

Temperature and Current Dependent Matching Fields in?Superconducting NbN Film

Patterned superconducting thin films having a periodic array of submicrometric pinning centers have been of great interest due to their excellence for the studies of the vortex pinning mechanisms in the type-II superconductors. Square hole array has been fabricated over a micro-bridge 60 mm??60 mm of NbN thin film by electron beam lithography. Previous works have been carried out in Nb, Pb and Al thin films where the vortex pinning effect is assumed to be small. In this work, we study the matching pinning effect by the artificial hole array in superconducting NbN thin films. We observed the interplay between the vortex quantization and the artificial hole array. Magneto-resistance minima at integer matching fields up to five times of H ₁ (the first matching field corresponding to one vortex inside each hole) and fractional matching fields at 1/2H ₁, 3/2H ₁ and 5/2H ₁ have been observed.     

Influence of Moderate Temperature Treatment on Thermal Cycling Behaviour and Mechanical Properties of the CuAINiMnTi Alloys

The influence of moderate temperature treatment after quenching on thermal cycling behaviour andmechanical properties of the CuAlNiMnTi shape memory alloys have been investigated.It is shownthat there will be α phase precipitation in the alloy when it is subjected to quenching followed bymoderate temperature treatment at 600℃.The precipitation of α phase can suppress NiAl-basephase precipitation during subsequent thermal cycling,therefore the stabilization of transformationtemperature during thermal cycling can be achieved.The suitable amount of α phase precipitationcontributes to the improvement of mechanical properties of the alloy by changing the fracturemorphology.     

Properties of Superconducting Rhenium as an Absorber for Magnetic Calorimeters

A still puzzling problem in the development of low temperature micro-calorimeters for the measurement of the ¹⁸⁷rhenium β-spectrum is the understanding of the thermalization of energetic electrons in the superconducting rhenium absorber. We studied metallic magnetic calorimeters (MMC) with single crystal rhenium absorbers and paramagnetic Au:Er temperature sensors. The energy released into the detector leads to a change of magnetization of the paramagnetic sensor located in a weak magnetic field. A SQUID with meander shaped inductance is used to read out this change. This setup allows the study of several properties of the superconducting absorber. The transition to the superconducting state is studied by measuring the magnetic flux expelled by the rhenium sample. The resistivity of rhenium above T _c can be estimated from the measurement of the spectral power density of the Johnson noise. Furthermore the quasiparticle lifetime can be investigated through the analysis of the shape of detector signals caused by intrinsic β-decays and the absorption of X-rays. We present the data obtained in these experiments and discuss the physical quantities which can be derived from these.      

Influence of Diffusion-Annealing Temperature on?the?Physico-Mechanical Properties of Au-doped Bi-2223 Superconductors

In order to investigate the influence of Au doping and diffusion-annealing temperature on the mechanical and superconducting properties of Bi-2223, Bi_1.8Pb_0.35Sr_1.9Ca_2.1Cu₃O _y superconductors were prepared by standard solid-state reaction methods. Doping of Bi-2223 was carried out by means of gold diffusion during sintering from an evaporated gold film on pellets. The investigation consisted of scanning electron microscopy, dc resistivity and hardness measurements. Electrical-resistivity measurements indicated that the room-temperature resistivity value decreased with decreasing diffusion-annealing temperature from 830 to 500?°C and these samples (G830, G800, G750, G700, G600 and G500) show the resistive behavior above the onset critical transition temperature with the zero-resistivity transition temperatures of 104 K, 80 K, 98 K, 95 K, 102 K and 103 K, respectively. To investigate mechanical properties of the samples, we have measured the diagonal length as a function of test load in the range of 0.245?C2.940 N. Mechanical properties (microhardness, Young??s modulus, yield strength and fracture toughness) of the samples are found to be load and diffusion-annealing temperature dependent. In addition, we have calculated the load independent hardness, Young??s modulus, yield strength, and fracture toughness of the samples. The possible reasons for the observed changes in superconducting and mechanical properties due to Au diffusion and diffusion-annealing temperature were discussed.     

Levitation Properties of Melt-Processed YBCO Bulk with a Linear Notch

In this paper, we report the levitation force properties of a melt-processed YBCO bulk with a linear notch. With the increase of the notch length, levitation force between the YBCO bulk and magnet decreases in exponential law with zero-field cooling (ZFC) condition and while its change obeys the polynomial form when the superconductor is cooled with magnetic field (FC). In addition, it is also found that the change of the area of levitation force hysteretic loop is very small in the case of FC, which means that critical current density is not obviously varied when the YBCO bulk has a linear notch. When the superconductor was cooled in zero magnetic field, the area increases sharply at first and then increases gradually; these results reveal the decrease of the critical current density of the superconducting bulk.     

Effect of La–Zn Substitution on the Structure and Magnetic Properties of Low Temperature Co-Fired M-Type Barium Ferrite

Ba(LaZn) _x Fe_12?2x O₁₉ (0≤x≤0.5) powders with Bi₂O₃ as an additive was synthesized by a sintered route at 900 °C or 950 °C. The structure and magnetic properties of La–Zn substituted M-type barium ferrites were also investigated. When 0≤x≤0.5, only one crystal phase existed in the sample, and the morphology of the grains were shown to be gradually irregular. The little amount of La³⁺ ions and Zn²⁺ ions changed the equilibrium of Fe²⁺ and Fe³⁺ at the 2a site, which increased the Fe³⁺–O–Fe²⁺ superexchange interaction strength, and the saturation magnetization (Ms) of the samples was also improved. Meanwhile, the substitution of La³⁺ and Zn²⁺ ions and the grains’ size bought great effects on the magnetocrystalline anisotropy field. As a result, with sintering at 950 °C for 6 h, the max Ms value of the samples with x=0.1 was 67.26 emu/g, and the minimum coercivity (H _c ) value was 1718.89 Oe with x=0.3, respectively.     

Temperature Modulation Measurements of the Thermal Properties of Nanosystems at Low Temperatures

We report on the dynamic measurements of thermal properties of nanosystems at very low temperatures. These techniques are based on the modulation of the temperature and hence leads to highly sensitive measurements. We will discuss the intrinsic limitations of these methods when the thermal properties of nano-objects are studied at very low temperatures, much below 1 K. Firstly, we will present thermal conductance measurements using the 3ω method. This technique is limited at low temperatures due to the significant increase of the mean free path. Secondly, heat capacity measurements using ac calorimetry are outlined, and again restrictions occur due to the continuous temperature gradient inherent to that technique. Propositions are made in order to overcome these limitations.     

Influence of Ni Doping on the Low Temperature Properties of Layered Fe1+δ Te

Low temperature studies on the layered iron telluride series Fe_1.1−x Ni _x Te (x=0.02, 0.04, 0.08, 0.12) have been carried out to investigate the influence of Ni doping on the structural and magnetic transitions of the iron telluride system. Magnetization studies as a function of temperature, M(T), in the range 3–300 K indicate an antiferromagnetic (AFM) transition in Fe_1.1Te, which shifts toward low temperature upon Ni doping. Neutron diffraction studies on Fe_1.1Te show that the AFM ordering is accompanied by a structural transition from tetragonal to monoclinic structure. In the case of Fe_1.1−x Ni _x Te with x=0.12, the structural and magnetic transition are both absent indicating the role of Ni in suppressing these transitions. While no signature of long-range magnetic ordering is found in the case of the Ni substituted compound, magnetization studies indicate that this compound exhibits a spin-glass like behavior.     

Effect of Critical Current Density and Critical Temperature on ac Susceptibility

Based on the flux creep equation, the effect of critical current density and critical temperature on ac susceptibility is investigated numerically in a superconducting slab immersed in an ac magnetic field. The current density dependence of the flux creep activation barrier is employed as the logarithmic law. The fundamental ac susceptibilities of the slab as a function of temperature for the same ac field have been derived in a unified picture. The results show that ac susceptibility in flux creep regime is affected by critical current density and critical temperature.     

Influence of Laser Coating on Microstructure and Properties of an Al-Si Alloy

The microstructure and wear resistance of acast Al-Si alloy coated with metal and rare earthelements and treated by the laser rapidmelt-solidification(LRMS)are studied in the pres-ent work.Optical and SEM micrographic analysesshowed that a superfine microstructure was ob-tained,and the hardness was remarkably enhancedby the LRMS treatment.Wear test showed that therapid melt-solidified microstructure had higherwear resistance than that treated by ordinary solidsolution treatment.     

Influence of Composition on Self-toughening and Oxidation Properties of Y-α-Sialons

Y-α-sialon ceramics with different compositions were hot-press sintered. Varying the m or n value in theα-Sialon general formula, both the α-sialon grain morphology and phase assemblages present diversification, therefore, affecting the toughness and hardness. Meanwhile, varying the compositional parameters also influenced the composition and structure of the intergranular glass phase, as well as its oxidation behavior at 1100-1200 ℃. The oxidation of the intergranular phase Mt in the Y-α-sialon ceramics was significantly enhanced with further rising the oxidation temperature to 1300 ℃.     

Effect of Thickness on the Structure and Tribological Properties of MoSx Coating

MoSx coatings were prepared by bipolar-pulse DC unbalanced magnetron-sputtering system with the variation of coating thickness at different Ar pressures.The composition and surface morphology were determined by using energy dispersive X-ray and scanning electron microscopy;the structural characterization was analyzed by X-ray diffraction.The friction and wear properties were investigated by fretting tests in air with less than 10% and 50% relative humidity.At 0.40 Pa pressure,(002) basal plane orientation was formed throughout the coatings.At 0.88 Pa and 1.60 Pa pressures,(002) basal plane orientation was only noticed in the first stage of coating growth(around 0.20 μm in thickness), and then edge orientations with their basal planes perpendicular to the surface would be evolved in the coatings.Humidity has a minor influence on the coatings that have(002) basal plane orientation,whereas the tribological properties of MoSx coatings with edge orientations are greatly affected by humidity.The mechanisms of coating growth and friction and wear processes are discussed.     

Effect of Sintering Temperature and Zinc Content on Some Properties of Li-Zn Ferrites

Li-Zn mixed ferrites with composition formula ZnxLi0.5-x/2Fe2.5-x/2O4 (0.2≤x≤0.8) were prepared by the usual ceramic method in 1000~1150℃. The effects of Zn substitution and sintering temperature on the formation, densification, microstructure and a.c. electrical conductivity have been studied. Under the effect of changing the firing temperature and Zn content, high sintered Li-Zn ferrite bodies are achieved. More fine structure bodies having high electrical resistance are obtained at high Zn content