Nickel embrittlement

Eastman J, Matsumoto T, Narita N, Heubaum N, Birnbaum HK. Hydrogen effects in nickel embrittlement or enhanced ductility In Bernstein IM, Thompson AW, editors. Hydrogen in Metals. New York AIME 1981. pp. 397-399. 

Carbon content is usually about 0.15% but may be higher in bolting steels and hot-work die steels. Molybdenum content is usually between 0.5 and 1.5% it increases creep—mpture strength and prevents temper embrittlement at the higher chromium contents. In the modified steels, siUcon is added to improve oxidation resistance, titanium and vanadium to stabilize the carbides to higher temperatures, and nickel to reduce notch sensitivity. Most of the chromium—molybdenum steels are used in the aimealed or in the normalized and tempered condition some of the modified grades have better properties in the quench and tempered condition. 

Aluminum is not embrittled by low temperatures and is not subject to external corrosion when exposed to normal atmospheres. At 200°C (400°F) its strength is less than half that at room temperature. It is attacked by alkahes, by traces of copper, nickel, mercuiy, and other heaw-metal ions, and by prolonged contact with wet insiilation. It suffers from galvanic corrosion when coupled to copper, nickel, or lead-... 

It is not subjected to hydrogen embrittlement as is tantalum, niobium and nickel alloys, and thus is able to sustain thermal and mechanical shock after exposure to gaseous hydrogen at high temperatures. 

Anodic oxide film properties depend upon ion concentration in acid chloride and in alkaline solutions films are more compact and crack-free in acid solution . Alloying with more than 47% of nickel gives good resistance to hydrogen embrittlement in potassium hydroxide solution . 

Pfeiffer contends that, in undeoxidised nickel at least, the low sulphur contents normally found are insufficient to cause grain-boundary embrittlement and that the latter is, generally, due to intergranular oxides. In the presence of sulphur-containing gases, however, the level of sulphur required. 

While carburisation itself is not a normal corrosion process, in that there is no metal wastage, absorption and diffusion of carbon can lead to significant changes in the mechanical properties of the affected material and in particular to marked embrittlement. Furthermore, initial carburisation can produce an acceleration of the normal oxidation process, a phenomenon that is notable in nickel-chromium alloys. 

Certain alloys of iron, nickel, and cobalt (Kovar, Fernico, etc.) have thermal expansion curves which nearly match those of borosilicate glasses, and a good bond may be formed between the two. Kovar is similar to carbon steel in its chemical properties. For example, it oxidizes when heated in air and is not wet by mercury. It may be machined, welded, copper brazed, and soft soldered. Silver solders should not be used with Kovar since they may cause embrittlement. At low temperatures Kovar undergoes a phase transformation, and the change in expansion coefficient below this temperature may be sufficient to cause failure of a glass-to-Kovar seal. The transformation temperature usually is below... 

G. Nickel. Nickel (nip 1,453°C), finds its primary use in the construction of apparatus to handle fluorine and volatile fluorides. In this situation the metal is rendered passive by a fluorine coating. Nickel plating is easily performed and provides a means of imparting corrosion resistance. The metal may be machined, silver soldered, copper brazed, or welded. However, the weld should be performed on clean surfaces because the presence of impurities containing lead, sulfur, phosphorus, and various low-melting metals leads to embrittlement and failure at the weld. 

Intergranular and transgranular cracking often occur simultaneously in the same alloy. Such transitions in crack modes are observed in alloys with high amounts of nickel, iron chromium and brasses. In corrosion under tension, ruptures are fragile and are sometimes characterized by the presence of cleavages, notably in the case of hydrogen embrittlement.16... 

Figure 6.71 Schematic showing the relation between the presence of some impurities and the grain boundary embrittlement processes that can lead to intergranular SCC of nickel...

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