Study of the sensitisation of a highly alloyed austenitic stainless steel, Alloy 926 (UNS N08926), by means of scanning electrochemical microscopy

Abstract

ElsevierLeiva García, R.; Akid, R.; Greenfield, D.; Gittens, J.; Muñoz Portero, MJ.; García Antón, J. (2012) AbstractThe feedback mode of scanning electrochemical microscope (SECM) was applied to study differences in the reactivity of a highly alloyed austenitic stainless steel, Alloy 926 (UNS N08926), in its unsensitised and sensitised state. Alloy 926 was heated at 825 ºC for 1 hour in an inert atmosphere in order to produce a sensitised metallurgical condition. Sensitisation was due to chromium carbide formation at the grain boundaries.The oxygen reduction reaction was used as an indicator to monitor the effect of the sensitisation process on the corrosion activity of the Alloy 926 surface in a 35 g l -1 NaCl solution. Higher oxygen consumption was observed above the sensitised sample than above the unsensitised sample due to differences in the oxide films of the two alloy conditions.

Electrochemical analysis of nanostructured iron oxides using cyclic voltammetry and scanning electrochemical microscopy

“…Deliberate addition of mediators is controversial in corrosion studies as they may influence the corrosion behavior [30]. Therefore, several SECM corrosion studies [20,[31][32][33][34][35] have exploited molecular oxygen O 2 naturally present in the solution. In the present paper we demonstrate how TSV-SECM using O 2 detection at nanostructured Pt MEs is applied to investigate and to identify redox processes from the complex voltammetric response of the electrocatalysts.…”

Role of Modern Localised Electrochemical Techniques to Evaluate the Corrosion on Heterogeneous Surfaces

“…One scheme of this effect is presented in Figure 2. However, sometimes the negative feedback is also observed when there is a competitive reaction between the tip and the substrate; this is the case when the oxygen reduction is the followed reaction and the substrate is a stainless steel [53]. On the other hand, the other modes of operation are the Generation Collection modes.…”

“…On the other hand, the other modes of operation are the Generation Collection modes. In the Tip generation/substrate collection (TG/SC) mode, the tip is held at a potential sufficient for an electrode reaction to occur and "generate" a product while the substrate is held at a potential sufficient for the product to react with or be "collected" by the substrate [53]. The reciprocal to this method is the substrate generation/tip collection (SG/TC), where the substrate acts to generate species that are measured at the tip.…”

“…On the other hand, other authors prefer a different approach to the problem using the SECM system. Some of the most relevant studies carried out are: visualization of local electrochemical activity and local nickel ion in weld Ni/Ti steels [82], characterisation of the electrochemical activity at the interface of a dissimilar explosive joint of stainless steel [83], evaluation of the effects of microplasma arc AISI 316L welds [84] or the study of the sensitisation of a highly alloyed austenitic stainless steel [53]. In the same way, the SVET technique can be used in the study of welds on order to determine the anodic and the cathodic sites of the heated samples.…”

“…Furthermore, according to the linear sweep voltammetry, the passivation current is higher in the case of the sensitised sample ( Figure 5). A higher passivation current indicates a 'lessprotective' passive film with higher electronic conductivity, this being due to the presence of areas depleted in alloying elements, notably chromium [53].…”