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Deterioration; Electric fields; Energy utilization; Ferrite; Free energy; High resolution transmission electron microscopy; Repair; Spinodal decomposition; Thermal aging, Decomposed microstructure; External electric field; Low energy consumption; Performance deterioration; Performance regeneration; Phase decompositions; Phase reconstruction; Thermal aging embrittlements, Duplex stainless steel
Abstract:
Duplex stainless steels suffer from thermal aging embrittlement that results from severe phase decomposition in ferrite phase after a long-term service at temperatures of 550–700 K, leading to the severe performance deterioration of duplex stainless steels. To ensure reliability and extend the service life of fabricated components made of duplex stainless steels, the development of techniques to efficiently and completely regenerate the deteriorated performance induced by spinodal decomposition and precipitation are extremely important. In this study, a novel pathway–an external electric field, is developed to eliminate the emerging Cr-rich (α′) phase and Fe-rich (α) phase resulting from spinodal decomposition as well as to dissolve the precipitates of G-phase in ferrite by introducing extra electrical free energy. The investigation is evidenced by microstructural and mechanical analyses using atom probe tomography, transmission electron microscopy, and nanoindentation. This high-efficiency (performance recovery above 90), low-energy consumption, online repair at the service temperature (700 K) is considerably superior to the traditional heat treatment process, which requires off-site repair at high temperatures (> 823 K). This new concept of manipulating precipitates using electric current to reconstruct the decomposed microstructure and achieve performance regeneration is expected to further stimulate the interest of researchers to extend the service life of materials by this means. © 2019 Acta Materialia Inc.
