The Role of Impurity Segregation in Cavity Nucleation
The presence of trace levels of impurities like sulfur, phosphorus, arsenic and others has a strong, and often deleterious, effect on the mechanical properties of metals and alloys. If such elements segregate to grain boundaries, the material tends to fail by brittle intergranular fracture at low temperatures, probably due to a reduction of the cohesive strength. Observations relating to this phenomenon, which is called temper embrittlement, are described in Section 8.1.1, and the-theory of cohesive strength in the presence of impurities is developed in Section 8.2.4. Impurities also influence the ductility under creep conditions. If they do so in an adverse manner this is called creep embrittlement. This may be caused by a reduction of the cohesive strength, but the precipitation of nonadherent particles also plays an important role (Section 8.1.2). Not all elements which are present in alloys in small quantities are harmful. Some elements such as carbon or zirconium are added deliberately to improve an alloy’s properties.
KeywordsPhosphorus Sulfide Zirconium Carbide Welding
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