High-Ni alloys

Fig. 3.1-125. The materials listed in Table 3.1-94 are the main representatives of high-Ni alloys.

As seen in fig. 11 the precipitation depends on both, the alloy composition and holding time. The Cr2N-formation has been reported by [Pickering, 1988] to be a major issue to high Cr and/or high Ni-alloys... 

Moreover, most international works, except the British one, tend to eliminate also for unacceptable postirradiation ductility, the high Ni alloys hardened via intermetallic precipitation. Therefore, investigations then focused on a selection of Fe bases with low Cr content and Ni content of up to 25%, hardened in solid solution by additions of Mo, Si, Ti -I- possibly Nb and V and also including variable additions of C, N, P, and B. The objective being to check the following points on these advanced austenitic bases compared with the reference 15-15Ti ... 

High Ni alloys (greater than 35% Ni) used either as base metals or as welding filler metals are a special concern in sulfidation conditions. Sulfidation of high Ni alloys can be especially rapid and yield corrosion... 

Extensive field experience has shown the 50 Cr/50 Ni and 60 Cr/40 Ni alloys to offer the best answer to controlling fuel oil ash corrosion. Type 446 stainless steel also shows acceptable corrosion rates but must be used judiciously due to its low strength at elevated temperatures and weldability. Since components of 50 Cr/50 Ni in contact with vanadium-sodium fuel ash melts still suffer high corrosion rates, they should be designed to minimize the amount of surface area available where ash may accumulate. 

The well defined change in compressibility of the fee alloy at 2.5 GPa clearly indicates the expected behavior of a second-order phase transition. The anomalously high value of the compressibility for the pressure-sensitive fee alloy is demonstrated in the comparison of compressibilities of various ferromagnetic iron alloys in Table 5.1. The fee Ni alloy, as well as the Invar alloy, have compressibilities that are far in excess of the normal values for the... 

Sulfur compounds, whether organic or inorganic in nature, cause sulfidation in susceptible materials. The sulfide film, which forms on the surface of much con-stmction materials at low temperatures, becomes friable and melts at higher temperatures. The presence of molten sulfides (especially nickel sulfide) on a metal surface promotes the rapid conversion to metal sulfides at temperatures where these sulfides are thermodynamically stable. High-alloy materials such as 25% Cr, 20% Ni alloys are widely used, but these represent a compromise between sulfidation resistance and mechanical properties. Aluminum and similar diffusion coatings can be of use. 

Fig. 12.12 An electrodeposit showing unusually high compressive stress. A ISO x ISO mm copper sheet was insulated with lacquer on one side and electroplated with Sn-3S Ni alloy. The high compressive stress has caused the sheet, originally flat, to coil in the manner shown, with...

Raney nickel is a useful catalyst for hydrogenations at mild conditions. It is, however, sensitive to poisoning and not very stable at high temperatures. Another disadvantage is that regeneration is not always possible in many cases the catalyst must be melted with aluminium until the right Al-Ni alloy is formed. Then the preparation procedure has to be repeated again. Moreover, the preparation procedure is not very reproducible. 

Fig. 8.38 (Left) The Mossbauer spectrum of the rock called Heat Shield rock, clearly shows with high intensity the mineral Kamacite, an Fe-Ni alloy with about 6-7% Ni (Right) The iron-nickel meteorite Meridiani Planum (originally called Heat Shield Rock ) at Opportunity landing site, close to the crater Endurance. The meteorite is about 30 cm across (Courtesy NASA, JPL, Cornell University)...

Material Quartz and ceramic materials (Barium titanate (BaTiOQ, Lead metaniobate (PbNb2Os) and the mixed crystal Lead-zirconate titanate) Nickel or an alloy of Nickel. Also, some other high-tech alloys with ferrite materials (MFe204, M = divalent metal like Ni, Zn and Pb)... 

The method can successfully be used in analyses of impurities in metals and alloys, for estimation of minor elements in monomolecular films of oxide layers of Fe-Cr-Ni alloys, for detection of metal impurities in environmental pollution, for studying the depression of high-grade semiconducting materials and for analysis of the corrosion products of contact junction diodes used in microelectronic circuits. Much sophistication is desirable on the instrumental side so as to incorporate an automatic recording device to make an FR polarograph suitable for wider applications and common use. 

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