Testing of Ni-base superalloy single crystals with circular notched miniature tensile creep (CNMTC) specimens

The present work introduces a novel circular notched miniature tensile creep (CNMTC) specimen which is used to study the influence of notches on creep and of multiaxial stress states on microstructural evolution in Ni-based single crystal (SX) superalloys. It is briefly discussed how mild circular n...

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Bibliographic Details
Published in:Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2018-01, Vol.712, p.223-231
Main Authors: Cao, L., Bürger, D., Wollgramm, P., Neuking, K., Eggeler, G.
Format: Article
Language:English
Subjects:
Axial stress
Cavity
Circular notched tensile specimens
Circularity
Creep
Creep (materials)
Evolution
Finite element method
Isotropic material
Microcrack
Microcracks
Ni-based superalloy single crystals
Nickel base alloys
Notches
Single crystals
Stress state
Superalloys
Tensile creep
Tensile strength
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Summary:The present work introduces a novel circular notched miniature tensile creep (CNMTC) specimen which is used to study the influence of notches on creep and of multiaxial stress states on microstructural evolution in Ni-based single crystal (SX) superalloys. It is briefly discussed how mild circular notches affect the stress state in the notch root of a tensile bar during elastic loading. Then the stress redistribution under creep conditions is calculated using the finite element method (FEM), assuming isotropic material behavior. Two series of interrupted creep experiments with the Ni-based single crystal superalloy ERBO1 (CMSX-4 type) were then performed at 950°C, with flat uniaxial miniature tensile creep (FUMTC) and CNMTC specimens, respectively. The evolution of cavities and microcracks in both types of specimens was carefully analyzed after 81, 169, and 306h. In the uniaxial experiments, a growth of cast pores and the formation of new creep cavities were observed. These degradation processes were much less pronounced in the circular notched specimens. The results of the present work are discussed in the light of previous findings on the influence of multiaxial stress states on creep in single crystal superalloys.
ISSN:0921-5093
1873-4936
DOI:10.1016/j.msea.2017.11.102