Microstructures of high-J c melt-textured YBa2Cu3O7−x /Ag superconductors

Silver has been previously added to the melt-textured YBa₂Cu₃O_7?x in order to increase the critical current density (J _c ) of these materials. However, the effect of this addition on theJ _c is presently unclear. The purpose of this study is to investigate the effect of silver on both critical current density and the microstructure of the melt-textured YBa₂Cu₃O_7?x superconductors by means of X-ray diffraction, optical polarized microscopy, and transmission electron microscopy (TEM). TheJ _c of the MTG YBCO/Ag samples is more than 10⁴A/cm² under the 5 kOe magnetic field. It has been shown that as the concentration of silver increases, the fraction of the 211 phase dispersed within the 123 matrix decreases. Therefore, theJ _c slightly decreases. These results, together with the effect of the 211 phase, dislocations, and other structure defects on flux pinning, are described in this paper.     

Metal Dusting of Fe–Cr and Fe–Ni–Cr Alloys Under Cyclic Conditions

Metal dusting is the disintegration of alloys into carbon and metal particles during high-temperature exposure to carbon-bearing gases. Model Fe–Cr and Fe–Ni–Cr alloys were studied to test the hypothesis that M₃C formation is necessary for metal dusting to occur. The alloys were exposed to a 68% CO–26% H₂–6% H₂O gas mixture at 680°C (a_c=2.9) under thermal cycling conditions. Equilibrium calculations predicted the formation of M₃C at the surface of Fe–25Cr, but not Fe–60Cr. All compositions were expressed in w/o, weight percent. Alloys of Fe–25Cr with 2.5, 5, 10, and 25 w/o nickel additions were also exposed to the same conditions to study the role of nickel in destabilizing the precipitation of M₃C and, hence, altering the resistance to metal dusting. Metal dusting was observed on all the alloys except Fe–60Cr. For Fe–25Cr, Fe–25Cr–2.5Ni, and Fe–25Cr–5Ni, the carbonization and dusting process was localized, and its incidence decreased in Fe–25Cr–2.5Ni, consistent with the increased destabilization of M₃C precipitation. However, Fe–25Cr–10Ni and Fe–25Cr–25Ni both underwent extensive dusting in the absence of protective Cr₂O₃ formation. The carbon deposits formed consisted of carbon filaments, which contained particles at their tips. These were shown by electron diffraction to be exclusively Fe₃C in Fe–25Cr, Fe–25Cr–2.5Ni, and Fe–25Cr–5Ni, and a mixture of austenite and (Fe,Ni)₃C in Fe–25Cr–10Ni and Fe–25Cr–25Ni.     

Microstructural evolution of a cold-deformed 6061Al reinforced with SiC particles during subsequent annealing

The microstructural development during annealing of a cold-deformed 6061Al metal matrix composite (MMC) reinforced with either 3 or 20 m diameter SiC particles has been investigated. The composites were compressed to low (< 10%) levels of strain and then annealed at either 350 or 450°C for different times. Microstructure examination was carried out by transmission electron microscopy and optical microscopy. The results reveal that prior grain boundaries and constituent particles are the dominant sites for recrystallization in both composites, although some nucleation was observed adjacent to the larger SiC particles. The concurrent presence of Mg₂Si precipitates affected the progress of recrystallization.     

Imaging and analysis of 3-D structure using a dual beam FIB

The application of focused ion beam instrumentation in the generation of three-dimensional microstructural data is described. The methodologies used to acquire and manipulate this data are explained, and the technique is illustrated by a number of examples from the material sciences. The limitations of this method, and practical pointers to the generation of meaningful data, are also discussed.     

Assessment of Corrosion Resistance and Metal Ion Leaching of Nitinol Alloys

Nitinol usage for biomedical implant devices has received significant attention due to its high corrosion resistance and biocompatibility. However, surface treatments are known to affect surface charge, surface chemistry, morphology, wettability, and corrosion resistance. In this investigation, the corrosion resistance of a binary and various ternary Nitinol alloys was determined after being subjected to electropolishing, magnetoelectropolishing, and water boiling and passivation. Cyclic polarization in vitro corrosion tests were conducted in Phosphate Buffer Saline (PBS) in compliance with ASTM F 2129-08 before and after surface treatments. The concentrations of dissolved metal ions in the electrolyte were also determined by ICPMS.     

A method of determining the time constant of the flat-plate solar collector

Analysis of the flat-plate solar water heating system indicates that the transient response of the system is determined by the time constants of the solar collector and storage tank. The time constants are dependent on the thermal capacitances and heat loss coefficients of the collector and storage tank and on the capacitance rate of the circulating liquid. This paper presents a method of determining the time constants of the system from test results on a solar simulator.     

Cyclic deformation behavior of high-purity titanium single crystals: Part I. Orientation dependence of stress-strain response

Randomly oriented single crystals of high-purity titanium were prepared by strain annealing and were subjected to multiple-step fatigue testing under strain-controlled conditions, in order to determine their cyclic stress-strain curves (CSSCs). These were found to fall into three groups, depending on orientation and the extent of slip and twinning. For those crystals oriented for single prismatic slip, a plateau was observed in the CSSCs, persistent slip bands (PSBs) occurred, and the plateau stress was 38 MPa. In a second group, oriented for prismatic slip but for which cross-slip and twinning was favored, the plateau was suppressed and the flow stresses were higher. In a third group, connected with orientations on the borders of the unit triangle, extensive hardening occurred, the CSSCs were steep, and there were multiple cases of slip and twinning. The results are interpreted in terms of maps in the stereographic projection recording the Schmid factors for the various deformation modes.     

Sliding wear behaviour of Ca α-sialon ceramics at 600 °C in air

As an extension of a previous investigation on the wear behaviour of Ca α-sialon ceramics of differing microstructures at room temperature, wear testing was conducted at 600 °C in air to explore the effects of microstructure, contact pressure and sliding speed on the wear behaviour. Under all loading conditions from 1 MPa to 1 GPa, a constant high friction coefficient was observed and a severe wear process was dominant, in which the sliding contact induced cracks were observed in different microstructures. Wear particles were generated along the wear track, but no tribofilm was detected. Increasing the sliding speed from 10 to 23 cm/s was found to significantly increase wear rate. However, variations in microstructure had little impact. That is, large elongated-grained α-sialon exhibited only a slightly lower wear rate than fine equiaxed-grained α-sialon.     

Modeling the economic disruption of a major earthquake in the San Francisco Bay Area: Impact on California

The paper presents a methodology for assessing the indirect effects of a natural disaster: the disruption of population and the local economy. The focus is earthquakes, with particular emphasis placed on the San Francisco Bay Area. The empirical analysis applies multiregional modeling techniques to measure the current impact of a major earthquake which directly affects seven San Francisco counties. The model and its inputs are discussed and the results presented in detail. Emphasis is given to the 58 California counties that are not in the earthquake zone but are affected economically.