Brass, representative alloys

Before considering the ordering transformation in AuCu, which is rather complex, we might examine the behavior of j5-brass. This alloy is stable at room temperature over a composition range of about 46 to almost 50 atomic percent zinc, and so may be represented fairly closely by the formula CuZn. At high temperatures its structure is, statistically, body-centered cubic, with the copper and zinc atoms distributed at random. Below a critical temperature of about 460°C, ordering occurs the cell corners are then occupied only by copper atoms and the cell centers only by zinc atoms, as indicated in Fig. 13-6. The ordered alloy therefore has the CsCl structure and its Bravais lattice is simple cubic. Other alloys which have the same ordered structure are CuBe, CuPd, and FeCo. 

Copper. Domestic mine production of copper metal in 1994 was over 1,800,000 t. Whereas U.S. copper production increased in the 1980s and 1990s, world supply declined in 1994. There are eight primary and five secondary smelters, nine electrolytic and six fire refiners, and fifteen solvent extraction—electro winning (SX—EW) plants. Almost 540,000 t/yr of old scrap copper and alloy are recycled in the United States accounting for - 24% of total U.S. consumption (11). New scrap accounted for 825,000 t of contained copper. Almost 80% of the new scrap was consumed by brass mills. The ratio of new-to-old scrap is about 60 40% representing 38% of U.S. supply. 

Between 1962 and 1982, pennies were made of brass, which is an alloy composed of 95% copper and 5% zinc. In 1982, the rising price of copper led to a change in the composition of the penny. Beginning in 1982, pennies have been made of zinc plated with copper. These pennies contain 2.5% copper and 97.5% zinc. In this experiment, the two different types of pennies will represent two isotopes of an element. 

Lead curse tablets from Roman Carthage contain variable amounts of very small metallic inclusions. Electron microprobe analysis confirmed these metallic inclusions were bronze, brass, and a Sn-Sb alloy. This was interpreted as possible evidence of lead metal recycling. Six samples were chosen to represent a range of tablets containing the minimum to the maximum number of inclusions. Thermal ionization mass spectrometry of the Pb isotopes in the curse tablets appear to define a mixing line, with the tablets containing the least number of inclusions plotting closest to the Tunisian lead ore isotope ratios. 

Cryogenic service is usually defined as temperatures below -100°C (-150°F). Properties of some cryogenic fluids are listed in Table 2.73. Valve materials for operation at temperatures down to -268°C (-450°F) include copper, brass, bronze, aluminum, 300-series stainless steel alloys, nickel, Monel, Durimet, and Hastelloy. The limitation on the various steels falls between 0° and -150°F (-17 and -101°C), with cast carbon steel representing 0°F (-17°C) and 3.5% nickel steel being applicable to -150°F (-101°C). Iron should not be used below 0°F (-17°C). 

Fourteen standard copper and brass alloys, the compositions of which have been certified by the National Bureau of Standards, have been used to calculate the concentrations of various elements in the coins (NBS C-1100. 1101, C-1102, 1106, C-1109, C-1111, C-1112, C-lllS, 1116, C-1120, 63C, 62D, 157A, and 158A). All standards were prepared metallographi-cally, ending with a diamond polish to obtain a surface representative of the interior of the standard. Excellent calibration curves were obtained with very good precision for both standards and coins, the calculated standard deviation is about 0.003% for Fe, 0.004% for Ni, 0.005% for Ag, 0.002% for Sn, 0.004% for Sb, and 0.003% for Pb. 

The notation hkl)[uvw specifies what is called an ideal orientation. Some metals and alloys have sheet textures so sharp that they can be adequately described by stating the ideal orientation to which the grains of the sheet closely conform. Most sheet textures, however, have so much scatter that they can be approximated symbolically only by the sum of a number of ideal orientations or texture components, and even such a description is inadequate. Thus, the deformation texture of brass sheet (70 Cu-30 Zn) is very near the ideal orientation (110)[Tl2]. But both the deformation and recrystallization textures of low-carbon sheet steel have so much scatter that the grain orientations present can be accurately represented only by a graphical description called a pole figure. 

Galvanic corrosion can usually be prevented by reasonable means (see below). Nevertheless, more or less serious cases of galvanic corrosion occur now and then. A drastic example concerns a safety valve on a foam tank with compressed air. Normally, the valve should open at a pressure somewhat above six bars. But because the valve ball material was low-alloy steel, and the valve housing was made of brass and other parts of martensitic stainless steel, the ball rusted and stuck to the seat. Together with other occasional malfimctions, this caused the tank to explode. Cases mentioned earlier (pp. 99 and 100) also represent examples of failure experienced in real life. 

The liberated azoimide attacks copper or its alloys (brass) and copper azides form on the metal surface. The concurrent use of LA and copper (or brass) in fuses or blasting caps therefore represents an inherent safety hazard. Although the LA-copper (copper alloys) reaction has been known since 1913, it has been a cause of many incidents decades later [49]. These incidents have been sometimes erroneously reported as spontaneous explosions. The reality, however, is that, in all known cases, they have been linked to some type of movement and therefore should not be considered spontaneous [70]. 

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