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Constant-stress miniaturized creep testing for single-phase, multi-phase and single crystalline nickel base high temperature alloys

Thursday (27.09.2018)
15:30 - 15:45 S1/01 - A1
Part of:

We introduce a customized-built micro-tensile creep testing setup with contactless DIC (Digital Image Correlation) strain measurement and feedback loop constant stress control. Creep behavior of miniaturized specimens with gauge length 1mm and rectangular cross sections between 0.04 ~ 0.16 mm^2 can be investigated. The setup accuracy was verified and limiting factors for specimen miniaturization were identified using a single phase, poly-crystalline Nimonic 75 alloy as reference material with well-known creep properties. As an additional result, we were able to continuously record and analyze the strain distribution evolution on specimens’ surface and the corresponding strain localization leading to final fracture with the DIC method and to correlate the strain distribution with the surface morphology of the specimens. Results will be presented and compared with similar investigations on NiAl single crystalline miniaturized specimens. The dominant factor for the evolution of creep damage in Nimonic 75 was grain boundary oxidation resulting in intergranular crack formation and early strain localization. Results of NiAl single crystalline show variation in creep strain rate and fracture strain with crystal orientation and an influence of specimen size as well. For miniaturized specimens of directionally solidified eutectic NiAl/Cr material, the influence of fiber orientation and misalignment on creep life is investigated. The observed findings will be explained in a mechanism-based consistent manner.

LiKang Luan
Karlsruhe Institute of Technology (KIT)
Additional Authors:
  • Dr. Heinz Riesch-Oppermann
    Karlsruhe Institute of Technology (KIT)
  • Prof. Dr. Martin Heilmaier
    Karlsruhe Institute of Technology (KIT)