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

作者：Suave Lorena Mataveli^*; Cormier Jonathan; Villechaise Patrick; Soula Aurelie; Hervier Zeline; Bertheau Denis; Laigo Johanne

来源：Metallurgical and Materials Transactions A-Physical Metallurgy and Materials Science, 2014, 45A(7): 2963-2982.

DOI：10.1007/s11661-014-2256-7

The microstructural evolutions occurring upon thermal aging of alloy 625 sheets were studied in the 823 K to 1173 K (550 A degrees C to 900 A degrees C) temperature range and for durations up to 2000 hours. TTT diagrams of the delta and gamma aEuro(3) phases were established based on high-resolution scanning electron microscopy and associated quantitative image analysis approaches. The evolutions of secondary carbide volume fraction were also characterized. It was observed that the precipitation domains of the gamma aEuro(3) and delta phases are, respectively, 823 K to 1023 K (550 A degrees C to 750 A degrees C) and 923 K to 1173 K (650 A degrees C to 900 A degrees C) and that the gamma aEuro(3) coarsening follows the LSW theory once these particles have an ellipsoidal morphology. The onset of grain growth, accompanied with an increase of the texture index, was observed at a temperature as low as 1173 K (900 A degrees C). It results from the progressive dissolution of grain boundaries%26apos; secondary carbides (especially M6C carbides) at this temperature, a process that favors a greater mobility of grain boundaries. It is also shown that the forming process (shear spinning), even after a relaxation heat treatment, enhances and stabilizes the precipitation of the delta phase compared to as-rolled + solution heat-treated sheets. It hence slows down the precipitation of the gamma aEuro(3) phase, a result that is in good agreement with a thermal aging that was performed under load (i.e., during a creep test).

• 出版日期2014-6