Embrittlement mechanism

Table 10.9 lists some common zinc anode alloys. In three cases aluminium is added to improve the uniformity of dissolution and thereby reduce the risk of mechanical detachment of undissolved anode material . Cadmium is added to encourage the formation of a soft corrosion product that readily crumbles and falls away so that it cannot accumulate to hinder dissolution. The Military Specification material was developed to avoid the alloy passivating as a result of the presence of iron . It later became apparent that this material suffered intergranular decohesion at elevated temperatures (>50°C) with the result that the material failed by fragmentation". The material specified by Det Norske Veritas was developed to overcome the problem the aluminium level was reduced under the mistaken impression that it produced the problem. It has since been shown that decohesion is due to a hydrogen embrittlement mechanism and that it can be overcome by the addition of small concentrations of titanium". It is not clear whether... 

In contrast to SCC of carbon and low-alloy steels in chloride, sulfide, and sulfuric acid environments by hydrogen-embrittlement mechanisms, cracking in several environments is attributed to passive-film cracking and/or active-corrosion-path anodic-dissolution penetration mechanisms (Ref 124). These environments include nitrates, hydroxides, ammonia, carbon-dioxide/carbonate solutions, and aqueous car-bon-monoxide/carbon-dioxide. Nitrate-bearing solutions are encountered in coal distillation and fertilizer plants hydroxide solutions in the production of NaOH and in crevices of steam boilers and ammonia cracking has occurred in tanks and distribution systems for agricultural ammonia applications. 

Evaluation of hydrogen absorption and permeation provides valuable information on the hydrogen evolution and hydrogen embrittlement mechanism. Devanathan-Stachurski [5,6] developed a technique to measure hydrogen permeation though metallic membranes. This technique is based on the assumption that the following conditions are established at each surface of the membrane under potentiostatic control ... 

Abstract This chapter discusses the role of simulation irradiation techniques in studies of radiation embrittlement mechanisms. The chapter first reviews characteristics and examples of test reactor irradiation, ion irradiation and electron irradiation. The chapter then discusses advantages and limitations of these techniques from the viewpoint of damage rate, sample volume and damage characteristics. 

It is widely known that radiation embrittlement behaviour of reactor pressure vessel (RPV) steels depends on various parameters such as material composition, neutron flux and irradiation temperature. Sound understanding and modelling of embrittlement mechanisms require systematic knowledge of effects of individual parameters and their synthesis on microstructural development and then mechanical properties. Most such knowledge has been obtained from single-parameter experiments using test reactor irradiation. This is because test reactor irradiation allows researchers to obtain mechanical property data together with microstructural data on materials with well-controlled chemical compositions under well-controlled irradiation conditions such as flux and temperature. Surveillance data in commercial power reactors are non-systematic in this context and relevant microstructural data are very scarce. 

In 2005, Debarberis et al. developed a semi-mechanistic model applicable to the WWER RPV steels. The embrittlement mechanisms, matrix damage, Cu-precipitation and phosphorus segregation were considered, resulting in the following equation ... 

In the development of a new correlation method, microstructural characterization of the surveillance materials of some PWR plants was also performed in order to understand the embrittlement mechanism of RPV steels with different Cu contents. At the same time, another test reactor irradiation project, the PLIM project, was also conducted by Japan Nuclear Energy Safety (JNES), where extensive microstructural characterization of base metals and weld metals with a wide range of chemical compositions in terms of Cu and Ni was performed using APT, transmission electron microscopy and positron annihilation to obtain new insights with the embrittlement mechanism at high fluences.The mechanism of embrittlement identified or confirmed in these projects was summarized as follows ... 

Ortner performed a preliminary assessment of the recent embrittlement correlation methods with the WRD and the PLOTTER Tool. One of the findings in the assessment was that the goodness-of-fit of the existing embrittlement correlation methods for a limited range of data, for example low-Cu materials, depends on the national databases. Our understanding of the embrittlement mechanisms has been greatly improved to date. Nevertheless, there might be still some hidden parameters that cause a national database effect. Further discussions not only on known unkowns but also unknown unkowns are necessary. 

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