Alloys sensitization

Aluminium alloys Sensitive to contaminants requires very clean welding attacked very rapidly in concentrations near 100% or with excess acetic anhydride... 

In mechanical fuses, where percussion primers are required, it seems fairly obvious that space requirements impose limits on the size of spring mechanisms or other physical modes of causing firing pins to move. The result is that, for fuses and other applications of this type, it becomes necessary to use primers of greatly increased sensitivity (Refs 6 8). This condition is illustrated with the M29A1 primer which is required to fire with an applied energy of 16 inch-ounces. This increased sensitivity is achieved by the use of thinner primer cup metal of softer alloy. Sensitivity can be further enhanced by the use of more sensitive priming mixt (Refs 2,6 20)... 

Fig. 7.57 Effect of carbon and nickel content on intergranular corrosion penetration rate of 1 8 wt% Cr-base stainless steels. Alloys sensitized for 100 h at 550 °C. Immersion in boiling 65% nitric acid. Pds., periods (48 h) of exposure. Redrawn from Ref 84...

Pits that reach a critical depth can act as crack initiation sites if they lead to a higher local stress intensity. The crack initiation time in this case corresponds to the incubation time of pits of a critical size. Alternatively, precipitation reactions at the grain boundaries can render an alloy sensitive to intergranular corrosion. The preferentially corroded grain boundary then serves as initiation site of a crack. Inclusions, preexisting microcracks, or other structural defects are also likely crack initiation sites. The crack initiation time, in this case, is defined as the time required for a crack to reach a detectable size. Crack initiation may also be the result of hydrogen formed by a corrosion reaction that may cause embrittlement of the metal or of successive ruptures of a passive film or tarnish layer, but these mechanisms are more important for the propagation than the initiation of cracks. Because of the multitude of possible crack initiation mechanisms, and because of the statistical nature of the phenomenon, it is not possible to predict the crack initiation time from first principles. 

Application of experimental devices allows to perform NDT of products, made out of materials of low density (Al-Mg - alloys, Be, plastics) with high defectoscopic sensitivity up to 0,5 %. Inch-size X-ray vidicons used complete with microfocal X-ray tubes and X-ray image enlargement method allow to obtain resolution up to SO pairs of lines per mm. 

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 spectrum of the alloy in Figure 8.19 shows pronounced differences. The shape of the Fermi edge is different from that of Cu or Pd and proves to be sensitive to the constitution of the alloy. The peak due to formation of the 3/2 core state of Cu is shifted by 0.94 eV in the alloy and broadened slightly. The two Pd peaks are also shifted, but only slightly, and are narrowed to almost 50 per cent of their width in Pd itself... 

Lead azide tends to hydrolyze at high humidities or in the presence of materials evolving moisture. The hydrazoic acid formed reacts with copper and its alloys to produce the sensitive cupric azide [14215-30-6] Cu(N2)2- Appropriate protection must be provided by hermetic sealing and the use of noncopper or coated-copper metal. 

Aqueous formaldehyde is corrosive to carbon steel, but formaldehyde in the vapor phase is not. AH parts of the manufacturing equipment exposed to hot formaldehyde solutions must be a corrosion-resistant alloy such as type-316 stainless steel. Theoretically, the reactor and upstream equipment can be carbon steel, but in practice alloys are required in this part of the plant to protect the sensitive silver catalyst from metal contamination. 

Ion implantation (qv) has a large (10 K/s) effective quench rate (64). This surface treatment technique allows a wide variety of atomic species to be introduced into the surface. Sputtering and evaporation methods are other very slow approaches to making amorphous films, atom by atom. The processes involve deposition of a vapor onto a cold substrate. The buildup rate (20 p.m/h) is also sensitive to deposition conditions, including the presence of impurity atoms which can faciUtate the formation of an amorphous stmcture. An approach used for metal—metalloid amorphous alloys is chemical deposition and electro deposition. 

Disadvantages associated with some organic solvents include toxicity flammabiHty and explosion ha2ards sensitivity to moisture uptake, possibly leading to subsequent undesirable reactions with solutes low electrical conductivity relatively high cost and limited solubiHty of many solutes. In addition, the electrolyte system can degrade under the influence of an electric field, yielding undesirable materials such as polymers, chars, and products that interfere with deposition of the metal or alloy. 

BP. These nitrile alloy membranes are compounded from PVC, flexibilized by the addition of butadiene—acrylonitrile copolymers, PVC, and other proprietary ingredients. Typically reinforced with polyester scrim, NBP membranes are 1 mm thick and have a width of 1.5 m. They ate ptedominandy used in mechanically fastened roofing systems. NBP membranes exhibit excellent teat and puncture resistance as well as good weatherabihty, and remain flexible at low temperatures. They ate resistant to most chemicals but ate sensitive to aromatic hydrocarbons. The sheet is usually offered in light colors. The physical characteristics of NBP membranes have been described (15). 

Barium- and calcium-bearing manganese siUcon is used as an inoculant in gray and ductile iron. The alloy contains 60—65% Si, 9—11% Mn, 4—6% Ba, 1—3% Ca, and 1—1.5% Al. The combination of barium, calcium, and manganese provides excellent chill reduction, improves the graphite stmcture, and minimizes section sensitivity in castings having thin and thick sections. 

Sodium does not form alloys with aluminum but is used to modify the grain stmcture of aluminum—silicon alloys and aluminum—copper alloys for improved machinabiUty. Sodium—gold alloy is photoelectricaHy sensitive and may be used ia photoelectric cells. A sodium—2iac alloy, containing 2 wt % sodium and 98 wt % 2iac, is used to deoxidi2e other metals. 

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