A Short Review of High-Temperature Wetting and Complexion Transitions with a Critical Assessment of Their Influence on Liquid Metal Embrittlement and Corrosion

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.