Effect of Aging Time on Microstructure and Mechanical Properties of IN617 Superalloy at 900 °C

Subject Areas :

mohsen  mehdizadeh ¹ (PHD student of School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran)
hassan  farhangi ² (Asisstent Professor of School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, Tehran, Iran)

Received: 2021-11-07 Accepted : 2022-01-20 Published : 2022-06-22

Keywords: Mechanical Properties, Microstructure, Aging, IN617,

Abstract :

Microstructural changes and mechanical properties of IN617 superalloy aged at 900 °C for different durations from one hour to 2000 hours were investigated in the present work. The optical microscope (OM), scanning electron microscope (SEM), transition electron microscope (TEM), X-ray diffraction (XRD) and hardness and tensile tests were used to investigate the microstructure and mechanical properties of aged alloys. A significant amount of intergranular carbides were observed in the microstructure of aged alloys even in the microstructure of alloy which was aged for one hour. Block-shape carbides were observed in the sample which was aged for one hour. It was observed that with increasing the aging time the morphology of the carbides changed to quasi-spherical, plate and rod shaped. The carbides were first formed along the grain and twin boundaries and then within the grains, and continues carbide layer was observed along the grain boundaries for the sample which was aged for 2000 hours. Most of the carbides were M23C6 and a small percentage of them were determined to be M6C. Furthermore, it was observed that a small amount of Ti(C,N) phase which was present in the as received sample was converted to carbides after aging for 1500 hours. γ' phase was only observed in the  microstructure of sample which was aged for one hour. Mechanical test results shown that  the hardness, ultimate strength at room temperature and at 750°C increased with increasing the aging time, but after 2000 hours of aging these properties decreased to the values of as received sample. The impact energy of the sample which was aged for 2000 hours was equivalent to 25% of as received sample due to the formation of a continues carbide layer along the grain boundaries. The fracture surface of the impact samples were investigated and it was observed that fracture mode changed from ductile for as-received sample to brittle intergranular fracture for the samples which were aged for more than 100 hours.

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