The basic concepts and new developments in the general areas of grain boundary segregation (adsorption), wetting, and complexion (interfacial phase-like) transitions are briefly reviewed. Subsequently, recent studies in several relevant areas are discussed. At the atomic level, the formation of bilayers in Ni-Bi and Cu-Bi have been observed and found to be the root cause for liquid metal embrittlement (LME). At the microstructural level, the presence of minor impurities or co-alloying elements can significantly enhance the intergranular penetration and liquid metal corrosion (LMC). Furthermore, triple-grain-line wetting by a liquid metal can occur at high temperatures, which may significantly affect corrosion resistance (for LMC), as well as LME. Somewhat surprisingly, Bi vapors can penetrate along the triple-grain lines in S-doped Ni specimens to form open channels, which can be considered as an unusual case of triple-line wetting by a vapor phase. A coherent theme of this review and critical assessment article is to explore the unrecognized, yet important, roles of high-temperature adsorption/segregation, wetting, and complexion transitions in LME and LMC.

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