Crystallographic Orientation Influence on the Serrated Yielding Behavior of a Single-Crystal Superalloy

Abstract

Since Ni-based single-crystal superalloys are anisotropic materials, their behavior in different crystal orientations is of great interest. In this study, the yielding behavior in both tension and compression for 〈001〉, 〈011〉 and 〈111〉 oriented materials at 500 °C has been investigated. The 〈011〉 direction showed a serrated yielding behavior, a great tension/compression asymmetry in yield strength and visible deformation bands. However, the 〈001〉 and 〈111〉 directions showed a more homogeneous yielding, less tension/compression asymmetry in yield strength and no deformation bands. Microstructure investigations showed that the serrated yielding behavior of the 〈011〉 direction can be attributed to the appearance of dynamic strain aging (DSA) and that only one slip system is active in this direction during plastic deformation.

Low-Cycle Fatigue Behaviour of a Ni-Based Single-Crystal Superalloy

“…However, regarding the ⟨001⟩ direction, no serrations are detected when applying the LCF cycles, instead this direction shows a more stable yielding. A previous study [8] suggests that a serrated yielding behaviour during montonic loading by the ⟨011⟩ direction partly is attributed to dynamic strain ageing (DSA), and it may be assumed that this occurs during LCF loadings as well. Another difference between the three directions is that the ⟨111⟩ direction exhibits a cyclic hardening, see Fig.…”

“…3. In that figure, also monotonic stress-strain curves from a previous study [8] are added, to be able to compare cyclic and montonic stress-strain curves. Generally, the cyclic stress-strain results agree well with the monotonic results for all tested directions.…”

“…This softening was explained by the creation of dislocation networks at the γ/γ ′ -interface and a slower time-dependent coarsening of the γ ′ -precipitates. It is a well known fact that Ni-based single-crystal superalloys show a tension/compression asymmetry in yield strength [7,8]. During LCF testing with R ϵ =-1 this asymmetry will have an influence since the stress levels will be different in tension compared to compression.…”

In- and out-of-phase thermomechanical fatigue of a Ni-based single-crystal superalloy

“…Therefore, it is not believed that the serrated yielding occurs due to twinning in this case. Instead, previous studies [10,11] have reported of a serrated yielding behaviour for the 011 direction, and it was discussed that dynamic strain ageing has occurred and also that only one slip system is active during plastic deformation in the 011 direction. If a serrated yielding behaviour during the first cycles will influence the TMF life has not been considered in this paper, but this may be of interest for future research.…”

Creep and Stress Relaxation Anisotropy of a Single-Crystal Superalloy

“…This behavior by the h011i direction has been shown before during tensile testing at 773 K (500°C). [28] In that study, one explanation for the serrated yielding behavior of the h011i direction was the occurrence of dynamic strain aging (DSA) within deformation bands with a high dislocation density. DSA is the interaction between solute atoms and moving dislocations and in areas with a high dislocation density DSA is more likely to occur.…”