Creep of CMSX-4 superalloy single crystals: Effects of misorientation and temperature
- Univ. of Cambridge (United Kingdom)
In order to better understand the creep performance of CMSX-4 superalloy single crystals, creep strain testing has been carried out on various specimens systematically misaligned by up to 20{degree} from <001>. At 750 C, significant primary creep is observed, the extent of which depends strongly upon small misorientations away from the <001>/<011> symmetry boundary. In this regime there is evidence of secondary creep which is associated with primary creep strain sufficient for two or more further {l_brace}111{r_brace}<11{bar 2}> systems to become active. At 950 C, tertiary creep if prevalent, there being little primary creep exhibited under the stress levels tested. Measurements of the shape change and the lattice rotation, as deduced from analysis of electron backscatter patterns in the scanning electron microscope (SEM), confirms that the macroscopic shape deformation is due to {l_brace}111{r_brace}<11{bar 2}> at 750 C but that this changes to {l_brace}111{r_brace}<1{bar 1}0> at 950 C. There appears to be evidence to suggest that the maximum creep rate in the primary regime can be correlated to the secondary rate, which is invariant with increasing creep strain, i.e. a steady state is reached. At higher temperatures where tertiary creep is prevalent, the misorientation dependence of creep deformation is less strong; its extent is rationalized on the basis of Schmid`s law. For the purposes of engineering design, it is suggested that the occurrence of {l_brace}111{r_brace}<11{bar 2}> and {l_brace}111{r_brace}<1{bar 1}0> deformation be associated with primary and tertiary creep; these should be modeled as two separate curves which are associated with hardening and softening, respectively.
- OSTI ID:
- 345102
- Journal Information:
- Acta Materialia, Journal Name: Acta Materialia Journal Issue: 5 Vol. 47; ISSN 1359-6454; ISSN ACMAFD
- Country of Publication:
- United States
- Language:
- English
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