Mechanical Properties and Microstructural Characterization of Aged Nickel-based Alloy 625 Weld Metal
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of the most interesting characteristics of the nickel-based superalloys is its high corrosion resistance to an aqueous chloride medium.[1] Furthermore, these alloys exhibit extraordinary resistance to a wide range of organic and mineral acids due to their excellent corrosion resistance properties, mainly, at high temperatures, and, therefore, are commonly found in the marine, aerospace, chemical, and oil and gas industries.[2–5] The alloy Inconel 625 stands out as one of the leading commercial Ni-Cr-Mo-Nb alloy grades.[2] The
CLEITON CARVALHO SILVA, EMERSON MENDONC¸A MINA´, and ELINEUDO P. MOURA are with the Departamento de Engenharia Metalu´rgica e de Materiais, Universidade Federal do Ceara´, Fortaleza, Ceara´, Brazil. Contact e-mail: [email protected] VICTOR HUGO C. DE ALBUQUERQUE is with the Programa de Po´s-Graduac¸a˜o em Informa´tica Aplicada, Universidade de Fortaleza, Fortaleza, Ceara´, Brazil. JOA˜O MANUEL R.S. TAVARES is with the Departamento de Engenharia Mecaˆnica, Faculdade de Engenharia, Instituto de Cieˆncia e Inovac¸a˜o em Engenharia Mecaˆnica e Engenharia Industrial, Universidade do Porto, Porto, Portugal. Manuscript submitted June 25, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
development of this alloy in 1964 was designed to meet the market of alloys for high-temperature service. However, with the discovery of its exceptional corrosion resistance, it also came to assume a prominent position in other applications, where corrosion resistance is essential.[1] In addition, the 625 nickel-based superalloy exhibits an outstanding combination of mechanical properties and resistance to pitting, crevice and intergranular corrosion due to the solid-solution strengthening effect of chromium, molybdenum and niobium in its nickel matrix, making precipitation-hardening treatments unnecessary.[1] However, elements such as Cr, Ti, Nb, and Mo are also strong precipitate formers. According to many studies, the presence of these elements influences the formation of the metastable c¢¢ phase (Ni3Nb), primary MC carbides where M denotes Nb and Ti. There are other types of carbides such as M6C, where M denotes Si, Ni, and Cr, and also M23C6 where M denotes mainly Cr and/or Mo.[6–9] Nevertheless, the high cost of nickel-based superalloys makes them unviable for massive applications in some situations. In order to overcome this obstacle and make the use of Ni-based alloys attractive to equipment
manufacturers, providing high service performance using this particular class of material overlays with Ni-based alloys on C-Mn low alloy and stainless steels have become an option in recent years.[10–12] During welding with the Inconel 625 alloy as filler metal, there is an intense microsegregation of elements, such as niobium and molybdenum, within the interdendritic regions causing the supersaturation of the liquid metal in its final stage of solidification.[10] This important phenomenon results in the precipitation of Nb-rich Laves phase and MC primary carbides of type NbC.[13,14] The segregation and precipitation
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