The Effect of Dilution on Microsegregation in AWS ER NiCrMo-14 Alloy Welding Claddings
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NICKEL-BASED superalloys are special materials that have excellent mechanical properties at high temperatures and show good resistance to corrosion and oxidation.[1] Due to these properties, these superalloys are used in nuclear power plants, the aeronautical industry, components for power-generation turbines, missiles for the arms industry, chemical and petrochemical processing plants as well as in the oil and gas industry.[2] Their excellent resistance to corrosion is associated with a very thin stable oxide layer, which protects the material from the external environment.[3,4] The chromium is responsible for forming the oxide layer, while the molybdenum increases resistance to localized corrosion by promoting repassivation of the oxide film.[5] The high cost of superalloys limits their application from an economic point of view.[6,7] However, to help overcome this issue, weld cladding is considered an alternative for manufacturing parts and equipment whose external or internal surfaces require specific properties that allow a satisfactory performance under the service conditions required.[6] Nonetheless, several metallurgical aspects of the weld claddings must be considered. For example, the crystalline structures of the substrate and deposit, as well as their properties, tend to make welding much more complex.[8,9] Moreover, there E´MERSON MENDONC¸A MINA´ and YURI CRUZ DA SILVA, Doctoral Students, and CLEITON CARVALHO SILVA, Professor, are with the Universidade Federal do Ceara´, Department of Metallurgical and Materials Engineering, Campus do Pici, Building 1080, Fortaleza, Ceara´, 60.455-760, Brazil. Contact e-mail: emina@ metalmat.ufc.br JEAN DILLE, Professor, is with the Universite´ Libre de Bruxelles, Brussels, Belgium, and Federal University of Rio de Janeiro, Rio de Janeiro, Brazil. Manuscript submitted January 29, 2016. Article published online October 6, 2016 6138—VOLUME 47A, DECEMBER 2016
are also various microchemical alterations, such as an increase of Fe and C, as a consequence of the dilution of the deposit with the substrate,[10] as well as microsegregation, which is a phenomenon that results from solidification under unbalanced conditions. Microsegregation also causes significant microchemical and microstructural changes, such as the nucleation of secondary phases.[11] Consequently, microsegregation affects the properties of these alloys and these microchemical alterations tend to potentialize susceptibility to localized corrosion.[12] Thus, a microsegregation evaluation is fundamentally important for applications where resistance to corrosion is required. The Inconel 686 alloy, the main alloy to be evaluated in this study, is considered to be one of the first third generation nickel-based superalloys. It was developed in 1992 to meet the needs of applications to be used under severe corrosion conditions.[13] The 686 alloy belongs to the Ni-Cr-Mo class with the addition of W, developed, at first, for equipment to purify gas from burning coal, commonly used in thermoelectric plants.[13] In add
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