Abstract
LONDON. Institute of Metals (Annual Autumn Meeting, Liverpool), Sept. 5.—R. May: Eighth report to the Corrosion Research Committee. Further investigations of ‘impingement attack’ were undertaken to interpret the results of certain tests on condenser tubes, and, in particular, to explain the relationship which appeared to exist between the effects of intermittent cavitation in the water and the effects of air-bubble impingement. The behaviour of protective films under various conditions of impingement has been studied by measurements of the ‘film potential.’ When there is no intermittent cavitation, ‘impingement attack’ can still take place as a result of air-bubble impingement, and it is concluded that there are two separate main causes of ‘impingement attack,’ namely, intermittent cavitation as shown by Sir Charles Parsons, and air-bubble ‘impingement‘ as shown by Dr. Bengough, R. Pirret, and the author. Both depend on the occurrence of rotating motions of the water.—Ulick R. Evans: Corrosion at discontinuities in metallic protective coatings. The cracks produced by bending are more dangerous than uniformly distributed pores. If the coating metal is cathodic to steel, the steel is corroded; copper under some conditions causes marked acceleration of the corrosion of steel at exposed places, nickel being less dangerous. If the coating metal is anodic to steel, the coating suffers corrosion preferentially, the steel thereby receiving protection; thus steel coated with zinc usually suffers no corrosion even at cracks until the zinc becomes exhausted. Steel thickly covered with zinc usually fares better than thinly covered steel, notwithstanding the greater tendency to cracking; old galvanised sheet carried more zinc than the modern material and generally lasted longer. Coatings of aluminium or zinc-iron alloys are themselves less attacked than coatings of free zinc, but for that very reason they afford less sacrificial protection to the underlying steel in certain waters. Zinc itself is rather rapidly attacked when partially immersed in a chloride solution, but alternate salt spraying and drying builds up a protective film.—A. G. C. Gwyer, H. W. L. Phillips, and Miss L. Mann: The constitution of the alloys of aluminium with copper, silicon, and iron. The ternary systems aluminium-copper-silicon and aluminium-copper-iron are considered. The former of these is eutectiferous, with a ternary eutectic of CuAl2, aluminium and silicon, containing 26 per cent, of copper, 6.5 per cent, of silicon, and freezing at 525° C. The aluminium-copper-iron system is rather more complex; a peritectic reaction occurs at 590° C. between FeAl3 and liquid resulting in the formation of a constituent isomorphous with ‘ X ’; the latter forms a ternary eutectic with CuAl2 and aluminium, containing 32.5 per cent of copper, 0.3 per cent of iron, and freezing at 542° C. A quaternary eutectic occurs at 26 per cent copper, 6.5 per cent silicon, 0.5 per cent iron, freezing at 520° C., the constituents being aluminium, CuAl2, ‘ X,’ and silicon. The paper deals exclusively with inetastable conditions.—C. J. Smithells, S. V. Williams, and J. W. Avery: Laboratory experiments on high-temperature resistance alloys. A series of nickel-chromium alloys containing from 10 to 60 per cent of chromium, and a few ternary alloys containing tungsten and molybdenum, have been made from specially pure materials melted in hydrogen. For the binary alloys resistance to oxidation increases with increase in chromium content up to 30 per cent. With more than 40 per cent of chromium, a second phase appears and resistance to oxidation falls. Ternary alloys containing only 10 per cent of chromium show low resistance, while those containing 20 per cent of chromium show high resistance to oxidation. For high resistance to oxidation the oxide layer must contain at least 50 per cent of chromic oxide. The composition of the oxide layer is determined by, but is not generally the same as, the composition of the alloy. For the binary alloys resistance to sag at high temperatures decreases with increase in chromium content. The ternary alloys sag more than the binary alloys having a similar nickel content. Small amounts of impurities lower both the resistance to oxidation and sag.—W. R. D. Jones: The copper-magnesium alloys, Part 3. Notched-bar impact tests on forged and heat-treated copper-magnesium alloys are discussed. There is no advantage in adding more than about 2 per cent of copper to magnesium; alloys containing more than 5 per cent are brittle. The embrittling effect is decreased as the temperature rises. On exposure to cold, the toughness of these alloys has been decreased. Forging breaks down the eutectic network, improving the mechanical pro perties. Heat-treatment increases slightly the size of the globules of Mg2Cu and the crystal grains, which are rendered equiaxed and more regular in size.—J. E. Malam: The Rockwell hardness test. The Rockwell ball test in its present form yields so-called ‘hardness numbers’ which are quantitatively mis leading. Unscientific results are also obtained owing to the arbitrary numbering of the scleroscope scale. The whole subject of hardness testing should be examined by a representative committee.
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Societies and Academies. Nature 122, 424–427 (1928). https://doi.org/10.1038/122424a0
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DOI: https://doi.org/10.1038/122424a0