Abstract
The deformation and fracture mechanisms of a single crystal nickel-based superalloy CMSX-4 have been investigated during low cycle fatigue (LCF) tests at temperatures of 750, 850, and 950 °C under strain-controlled R = 0. It was found that LCF lives at 750 and 850 °C were similar and longer than those at 950 °C. The specimens tested at 750 and 850 °C showed fatigue crack initiation at internal pores, and their failure occurred by cracking at persistent {111} slip bands. On the other hand, at 950 °C the crack initiated at the oxide-layered surface and propagated along <100> γ channel until fracture. At the two lower temperatures, a/2<110> dislocations with low density was rarely present within γ channels, and a/3<211> partial dislocations were occasionally seen to shear γ′ leaving superlattice stacking faults behind. At 950 °C, homogeneous deformation was produced by perfect dislocation movements of cross-slip and climb in the γ channel and a limited γ′ shearing by superdislocation was observed. At total strain range lower than 0.6%, well-developed polygonal dislocation network formed at rafted γ′ interface. Comparison of dislocation structures revealed that load-controlled LCF tests lead to more severe deformation to specimens than strain-controlled tests.
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The authors acknowledge the financial support of MKE (Ministry of Knowledge Economy), Account No. UCN248-2865.C, which made this work possible.
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Hong, H.U., Choi, B.G., Kim, I.S. et al. Characterization of deformation mechanisms during low cycle fatigue of a single crystal nickel-based superalloy. J Mater Sci 46, 5245–5251 (2011). https://doi.org/10.1007/s10853-011-5462-3
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DOI: https://doi.org/10.1007/s10853-011-5462-3