Characterization of Fatigue Crack Growth Behaviour of Alloy 617M Base and Weld Material

• Published in: Procedia Structural Integrity Vol. 60; pp. 136 - 148
• Main Authors: Rakim, Md, Basu, P., Jana, M., Choudhury, S., Acharyya, S.K., Babu, M. Nani, Moitra, A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 2024
• Subjects: Ageing; Alloy 617M; Fatigue crack growth (FCG); Threshold stress intensity factor (∆KTH); Fatigue crack growth (FCG); Alloy 617M; Threshold stress intensity factor (∆KTH); Ageing
• ISSN: 2452-3216; 2452-3216
• DOI: 10.1016/j.prostr.2024.05.036

Alloy 617M is a Ni-based super-alloy made in the form of tubes which are used in high-temperature boilers and super heaters in Advanced Ultra Super Critical (AUSC) power plants. The high-temperature oxidation and mechanical properties of this material have been derived based on chromium (Cr), cobalt (Co) and molybdenum (Mo) as prime alloying elements which cause solid solution strengthening, carbide precipitation (M23C6, M6C) and formation of intermetallic phase Ni3(Al, Ti) (γʹ-phase). The manufacturing route of these components involve bending and welding operations which are critical locations and potential sites for crack nucleation and growth. Also, the conjoint influence of high temperature and flow-induced vibrations in the tubes further aides to crack nucleation and growth. Thus, fatigue crack growth (FCG) properties are important. Therefore, in this work, detailed experimental studies on the FCG behaviour of Alloy 617M base and weld materials have been carried out at different test temperatures (27 °C, 650 °C, 710 °C and 750 °C). The effect of ageing (1000, 2000, 5000 and 20000 hours) at an operating temperature of 710 °C on FCG has also been evaluated. All the FCG tests have been conducted as per ASTM with a constant load ratio (R = 0.1) and frequency of 15 Hz. From the experimental results, a major trend is observed of decreasing threshold stress intensity factor (ΔKTH) with an increase in ageing time and test temperature. The variations in the ΔKTH with test temperature and ageing time have been discussed and the crack growth mechanism has been established through microstructure and fractographic studies validating from existing literatures.