Alloys defects

H. Mehrer and W. Dorner. Diffusion in amorphous alloys. Defect and Diffusion Forum, 66-69 189-206, 1989. 

H.J. Grabke. Surface and interface reactions and diffusion during the high-temperature corrosion of matals and alloys // Defect Diffusion Forum.- 2001.- V.194-199.-P.1649-1660. 

Samples with particles below 100 nm provide challenges to the typical diffraction experiment. For example, alloys, defects and lack of long-range order in nanoparticle samples result in smearing of Bragg peaks and failed analyses. 

Representative set of weldments was examined site welds (with pearlitic type weld metal) and two types of site weld repair zones with different welding technologies using Cr-Ni filler metals and Ni-based alloy. Results of AUGUR 4.2 inspection were compared with manual ultrasonic inspection ones in terms of defect detection, characterization, positioning and sizing in order to estimate correlation between these data. 

The sensitivity tests are carried out on artificial defects (nickel-chromium specimens of NFA 09.520,see figure 3 of annex 1) and natural defects (one part in "light" alloy, one part in stellite grade 1 containing micropores, 2 specimens of fracture mechanical type CT20 in Z2 CN 12.10 (NFA 03.180). 

The weld depths penetration for gold-nickel alloy and tantalum cylinders have been well controlled by an entirely contactless ultrasound method. Nevertheless, the development of signal and image processing will allow to increase the resolution of the ultrasonic images. Moreover, in order to be able to size quite well the lacks of weld penetration, the simulation of the interaction beam-defect is presently developed in our laboratory. 

Fig. VIII-2. Scanning tunneling microscopy images illustrating the capabilities of the technique (a) a 10-nm-square scan of a silicon(lll) crystal showing defects and terraces from Ref. 21 (b) the surface of an Ag-Au alloy electrode being electrochemically roughened at 0.2 V and 2 and 42 min after reaching 0.70 V (from Ref. 22) (c) an island of CO molecules on a platinum surface formed by sliding the molecules along the surface with the STM tip (from Ref. 41).

Lea.dAnodes. A principal use for lead—calcium—tin alloys is lead anodes for electrowinning. The lead—calcium anodes form a hard, adherent lead dioxide layer during use, resist corrosion, and gready reduce lead contamination of the cathode. Anodes produced from cast lead—calcium (0.03—0.09 wt %) alloys have a tendency to warp owing to low mechanical strength and casting defects. 

Wrought lead—calcium—tin anodes have replaced many cast lead—calcium anodes (14). Superior mechanical properties, uniform grain stmcture, low corrosion rates, and lack of casting defects result in increased life for wrought lead—calcium—tin anodes compared to other lead alloy anodes. 

MgCl2-Supported Catalysts. Examination of polymerizations with TiCl catalysts has estabUshed that only a small percentage of titanium located on lateral faces, edges, and along crystal defects is active (52) (see Titanium and titanium alloys). This led to the recognition that much of the catalyst mass acted only as a support, promoting considerable activity aimed at finding a support for active titanium that would not be detrimental to polymer properties. 

Amorphous Silicon. Amorphous alloys made of thin films of hydrogenated siUcon (a-Si H) are an alternative to crystalline siUcon devices. Amorphous siUcon ahoy devices have demonstrated smah-area laboratory device efficiencies above 13%, but a-Si H materials exhibit an inherent dynamic effect cahed the Staebler-Wronski effect in which electron—hole recombination, via photogeneration or junction currents, creates electricahy active defects that reduce the light-to-electricity efficiency of a-Si H devices. Quasi-steady-state efficiencies are typicahy reached outdoors after a few weeks of exposure as photoinduced defect generation is balanced by thermally activated defect annihilation. Commercial single-junction devices have initial efficiencies of ca 7.5%, photoinduced losses of ca 20 rel %, and stabilized efficiencies of ca 6%. These stabilized efficiencies are approximately half those of commercial crystalline shicon PV modules. In the future, initial module efficiencies up to 12.5% and photoinduced losses of ca 10 rel % are projected, suggesting stabilized module aperture-area efficiencies above 11%. 

Electrical conductivity of copper is affected by temperature, alloy additions and impurities, and cold work (9—12). Relative to temperature, the electrical conductivity of armealed copper falls from 100 % lACS at room temperature to 65 % lACS at 150°C. Alloying invariably decreases conductivity. Cold work also decreases electrical conductivity as more and more dislocation and microstmctural defects are incorporated into the armealed grains. These defects interfere with the passage of conduction electrons. Conductivity decreases by about 3—5% lACS for pure copper when cold worked 75% reduction in area. The conductivity of alloys is also affected to about the same degree by cold work. 

Ferrous-aUoy-clad tube sheets are generally prepared by a weld overlay process in which the alloy material is deposited by welding upon the face of the tube sheet. Precautions are required to produce a weld deposit free of defects, since these may permit the process fluid to attack the base metal below the alloy. Copper-aUoy-clad tube sheets are prepared by brazing the alloy to the carbon steel backing material. 

Use fully killed or fine grain steel, controlled rolling temperatures high Mn/C ratios eliminate sharp corners in design, remove defects from steel heat treat steel. For cryogenic operations use high nickel alloy steels or austenitic stainless steels, depending on temperature. 

By way of example, Volume 26 in Group III (Crystal and Solid State Physics) is devoted to Diffusion in Solid Metals and Alloys, this volume has an editor and 14 contributors. Their task was not only to gather numerical data on such matters as self- and chemical diffusivities, pressure dependence of diffusivities, diffusion along dislocations, surface diffusion, but also to exercise their professional judgment as to the reliability of the various numerical values available. The whole volume of about 750 pages is introduced by a chapter describing diffusion mechanisms and methods of measuring diffusivities this kind of introduction is a special feature of Landolt-Bornstein . Subsequent developments in diffusion data can then be found in a specialised journal. Defect and Diffusion Forum, which is not connected with Landolt-Bdrnstein. 

NaCl structure, superconductor below 3.5 K), SotAss (defect NaCl structure, superconductor below 1.2K). The many important industrial applications of dilute alloys of As, Sb and Bi with tin and lead were mentioned on pp. 370 and 371. 

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