Evolution of creep rupture mechanism in advanced powder metallurgy superalloys with tantalum addition

• Published in: Journal of alloys and compounds Vol. 925; p. 166713
• Main Authors: Bai, J.M., Zhang, H.P., Li, X.Y., Liu, J.T., Sun, Q.S., Liu, C.S., Zhang, Y.W.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 05-12-2022; Elsevier BV
• Subjects: Crack propagation; Creep life; Creep rupture mechanism; Damage; Fracture surfaces; Microtwins; Ni-base superalloys; Nickel base alloys; Nucleation; Powder metallurgy; Rupture tests; Superalloys; Tantalum; Twin boundaries; Creep rupture mechanism; Tantalum; Ni-base superalloys; Powder metallurgy
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2022.166713

To further understand the effect of Ta additive on the creep damage for polycrystalline Ni-base superalloys, creep rupture tests on powder metallurgy (PM) superalloys with various Ta were carried out under different conditions in this study. The results indicated that the multiple crack propagation and damage mechanisms could occur at the identical creep condition. These different fracture mode areas had distinct boundaries on the fracture surface, its size could be altered by Ta addition. However, the effects of Ta were radically changed by the creep conditions. The creep rupture mechanism transformed significantly with temperatures and applied stresses, and even subversive laws appeared in the creep life for high-Ta alloys. The substructure observation after creep rupture demonstrated that the annealing coherent twin boundaries gradually lose coherence with the matrix, which could become sites for cavities nucleation or crack propagation that followed. Furthermore, the creep-induced microtwins were critical for the creep damage and rupture. The electron back-scattered diffraction (EBSD), high-resolution transmission electron microscope (TEM) imaging, and quantitative elemental analysis assisted in comprehending these alterable creep rupture mechanisms.
•Local incoherence occurs at coherent twin boundaries after creep rupture.•The creep-induced microtwins have strong interactions with the interface, causing severe curvature.•The segregation of Mo and Cr at grain boundaries increases with Ta content.•The tertiary creep damage accelerates rapidly when Ta addition exceeds the optimal concentration at high temperature creep.