Preparation technique and alloying effect of aluminide coatings as tritium permeation barriers: A review

Effect of Steel Substrates on the Formation and Deuterium Permeation Resistance of Aluminide Coatings

“…The ECD technique, i.e. ionic liquid (IL) plating [14], was employed to prepare Al coatings on Cr steel substrates. The electrolyte was synthesized with 1-ethyl-3-methylimidazolium chloride (EMIC, 64.5 wt %, Zhejiang Univ., Hangzhou, China) and anhydrous aluminum chloride (AlCl 3 , 35.5 wt %, Sigma-Aldrich, St. Louis, MO, USA).…”

“…The process of aluminization is forming a transition layer of (Fe, Al) solid solution and/or Fe-Al metallic compounds on the substrate surface via interdiffusion between Al atoms from a certain Al source and Fe atoms from steel substrates [14]. After 500 • C, 4 h heat treatment in vacuum, single-layered Fe 2 Al 5 -type aluminide coatings formed on these three types of Cr steel substrates, as shown in Figure 4.…”

“…For each steel type, the best aluminide TPBs thus may not have been achieved. As a result, the compactness and integrity of scales (also crucial for coating performance [14]) formed on different steels deviated, which could partly be observed from the section features shown in Figure 6a-c. From this point of view, it can be inferred that the substrates themselves played a part in the formation of aluminide TPBs, resulting in the deviation of deuterium resistance.…”

“…Recently, although Pedraza et al [8] have reported that there is a significant mismatch between aluminide coatings and steel substrates, which could lead to tensile cracks, aluminide coatings still showed good stability after steam exposure for 2000 h. However, aluminide TPBs often exhibit much lower actual performance than predicted based on bulk material properties [9,10]. One of the most possible reasons may be alloying elements from the steel substrate or Al source, and microstructures of substrate materials such as crystal and metallographic structures may also exert some influence on coating formation and performance [10][11][12][13], which could be called an alloying effect including a substrate effect and a doping effect in aluminide coatings [14]. The latter originates from doped species in the Al source or predeposited species on the substrate [14].…”

“…One of the most possible reasons may be alloying elements from the steel substrate or Al source, and microstructures of substrate materials such as crystal and metallographic structures may also exert some influence on coating formation and performance [10][11][12][13], which could be called an alloying effect including a substrate effect and a doping effect in aluminide coatings [14]. The latter originates from doped species in the Al source or predeposited species on the substrate [14]. Presently, however, aluminide TPB studies are mainly devoted to preparation technique and performance optimization.…”