Microstructural Evolutions During Thermal Aging of Alloy 625: Impact of Temperature and Forming Process

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INCONEL alloy 625 is a nickel-based superalloy developed close to 60 years ago to achieve a unique combination of mechanical strength, fracture toughness, fabricability, weldability, and corrosion resistance under aggressive environments both at room and high temperatures.[1–4] This alloy is widely used in the petrochemical, marine, nuclear, power generation, and aerospace industries.[1–9] Typical applications of alloy 625 are process tubing, bubble caps, distillation columns LORENA MATAVELI SUAVE, Ph.D. Student, is with the Physics and Mechanics of Materials Department, Institut Pprime, UPR CNRS no. 3346, CNRS – Universite´ de Poitiers – ISAE-ENSMA, 1 avenue Cle´ment Ader, BP 40109, 86961 Futuroscope, Chasseneuil, France, and also with the Materials and Process Department, Aircelle – SAFRAN Group, route du pont VIII, 76700 Gonfreville-L’Orcher, France. JONATHAN CORMIER, Associate Professor, PATRICK VILLECHAISE, Director of Research at CNRS, and DENIS BERTHEAU, Research Engineer at CNRS, are with the Physics and Mechanics of Materials Department, Institut Pprime, UPR CNRS no. 3346, CNRS – Universite´ de Poitiers – ISAE-ENSMA, 1 avenue Cle´ment Ader, BP 40109, 86961 Futuroscope, Chasseneuil, France. Contact e-mail: [email protected] AURE´LIE SOULA, Metallic Materials Engineer, formerly with the Materials and Process Department, Aircelle – SAFRAN Group, route du pont VIII, 76700 Gonfreville-L’Orcher, France, is now with the 50 rue Pierre Curie, BP 50042, 78371 Plaisir Cedex, France. ZE´LINE HERVIER, Mechanics of Materials Engineer, is with the Materials, Processes and Investigations Department, Turbomeca – SAFRAN Group, 64511 Bordes Cedex, France. JOHANNE LAIGO, Forged Ni-based Alloys Engineer, is with the Materials and Process Department, Snecma – SAFRAN Group, Site de Villaroche, RondPoint Rene´ Ravaud, 77550 Moissy-Cramayel, France. Manuscript submitted May 18, 2013. Article published online March 19, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A

for the petrochemical industry,[9,10] heat exchangers and reactor core in pressurized water reactors in the nuclear industry,[7] and weldings for marine application.[5] Alloy 625 is also used as turbine shrouds, spray bars, hydraulic tubing, armoring, and thrust reverser systems in the aerospace industry. Moreover, its use as plugs for the exhaust parts will gradually increase to meet the requirement of higher operating temperatures in new generations of civil aeroengines, temperatures which will prevent engine manufacturers from using Ti-based alloys. Since these aeroengine components are submitted to a wide range of thermomechanical loadings and to complex thermomechanical histories resulting from the very different operating conditions encountered during regular flights (e.g., take-off, cruise, approach, or landing regimes), the microstructure of alloy 625 is highly likely to evolve with possible consequences on the mechanical properties of the as-processed components. Indeed, while alloy 625 was originally designed as a solidsolution-strengthened alloy