PSI - Issue 52

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Marie Kvapilova et al. / Procedia Structural Integrity 52 (2024) 89–98 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 12. SEM images of the fracture surface of specimen crept at 900°C/200 MPa: (a) the low-resolution image, and (b) detail of interdendritic mode of creep fracture. The fractographic investigations of the fracture surfaces clearly indicate that the creep fracture is mostly brittle interdendritic and intergranular modes. The features of creep fracture surfaces of the GTD 111 specimens crept at 800 and 900°C are shown in Figs. 11 and 12. Macroscopic views of fractures (Figs. 11(a) and 12(a)) are indicating that superalloy under investigation withstand high strain concentration without necking where the dominant damage mechanism is a local strain-induced instability of dislocation microstructure leading to a loss of an external section of specimen. However, while at 800°C the final fracture is initiated of by the quasi-cleavage way (Fig. 11(b)), at higher testing temperatures the final fracture completely proceeds by interaction of damaged microvolumes. (Fig. 12(b)). 4. Conclusions Uniaxial constant-load creep tests of as-cast GTD 111 superalloy were carried out at 800, 900 and 950°C in a tensile stress range from 125 to 7MPa. The main results are summarized as follows: (i) creep tests were performed in power-law (dislocation) creep regime where creep flow is controlled by climb of mobile dislocation, (ii) two different creep damage mechanisms were identified, namely, interface decohesion between carbides/matrix and a breakage of the grain boundary M 23 C 6 carbides and (c) the final creep fractures were interdendritic and intergranular brittle mode. Acknowledgements The authors acknowledge the financial support for this work provided by the Technology Agency of the Czech Republic through Grant No. FW03010190. Stimulating discussion with Professor Karel Hrbáček ha s been of great value. References Wangyao, P., Polsilapa, S., Chaishom, P., Zrnik, J., Homkrajai W., Panich, N., 2008. Gamma Prime Particles Coarsening Behavior at Elevated Temperatures in Cast Nickel-Based Superalloy, GTD-111 EA. High Temperature Materials and Processes 27, 41-49. Wongnawapreechachai, P., Hormkrajai, W., Lothongkum, G., Wangyaao, P., 2012. Effect of Temperature Dropping During Reheat Treatments on GTD-111 Microstructure. High Temperature Materials and Processes 31, 113-123. Lee, H.-S., Kim, D.-S., Yoo, K.-B., Song, K.-S., 2012. Quantitative Analysis of Carbides and the Sigma Phase in Thermally Exposed GTD-111. Metals and Materials International 18, 287-293. Bera hmand, M., Sajjadi, S.A., 2012. An Investigation on the Coarsening Behavior of γ´precipitate in GTD -111 Ni-base Superalloy. Phase Transactios 85, 1-12. Turazi, A., de Oliveira, C.A.S., Bohorquez, C.E.N., Comeli, F.W., 2015. Study of GTD-111 Superalloy. Microstructure Evolution During High Temperature Aging and After Rejuvenation Treatments. Metallography, Microstructure, and Analysis 4, 3-12.