Anwendbarkeit einer Marker-Technik zur Unterstützung von Rißwachstumsuntersuchungen in spröden und duktilen Ni-Legierungen bei 500 und 750 Grad Celsius
Schwarze, D. (Corresponding author)
Schubert, F.
Publikationen vor 2000; PRE-2000; Retrocat
Jülich Forschungszentrum Jülich, Zentralbibliothek, Verlag 1999
164 p.
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Book
Addenda
Berichte des Forschungszentrums Jülich 3728
OpenAccess
OpenAccess
Please use the identifier: http://hdl.handle.net/2128/23138 in citations.


The crack growth behaviour of materials for application in turbines at temperatures of 500- 750 °C has been investigated. The creep and fatigue service loadings of a real turbine clisc were simulated by introclucing hold-times. The materials tested were the superalloy PM N18, Inconel 617 and the intermetallic phase $\beta$-NiAl of nominally stoichiometric composition. The crack growth tests were conducted in air and in vacuum (10$^{-5}$ mbar) to assess the influence of the test atmosphere. One of the main objectives was to clevelop a marker methocl and its application, as support for the crack growth tests carried out. The width of the marker required for the marker bands could be chosen through the number of stress cycles or the crack growth increment in the marker-cycle. At 500 °C, the crack surfaces of the CT specimens of Inconel 617 and PM N18 exhibited mixed fractures with trans- and intercrystalline regions. The fracture development could be divided into three, classical parts. At his temperature for both alloys the K$_{I}$ concept for the evaluation of the crack growth may be used. The RCT specimens of the intermetallic phase $\beta$-NiAl fractured in a completely brittle manner with no measurable time to failure. At 500 °C, Inconel 617 and especially PM N18 were well suited to the use of the marker method. Measurements of the distauces between the marker bands gave a goocl estimate of the crack growth rates. At the higher test temperature of 750 °C, the crack growth rates and the proportion of intercrystalline fracture increased for Inconel 617 and PM N18. In all three materials, the formation of pores and dimpled fracture was observed, especially at high $\Delta$K$_{I}$ values, and the coarse-grained $\beta$-NiAl exhibited higher crack growth rates than the fine-grained material. For this temperature the evaluation of the crack growth experiments should be by the K$_{I}$ concept for PM N18 and for Inconel 617 the C* concept is recommended. At the higher test temperature, the increasecl plasticity of Inconel 617 and $\beta$-NiAl made the application of the marker method difficult. The superalloy PM N18 was well suited to the marker method even at 750 °C. An acceleration of the crack growth in air at 500 °C compared to that in vacuum was observed only for Inconel 617. At 750 °C, both coarse-grainecl and fine-grained $\beta$-NiAl exhibited higher crack growth rates in air than in vacuum.