The influence of crystal orientation on the high temperature fatigue crack growth of a Ni-based single crystal superalloy
- Oxford Univ. (United Kingdom). Dept. of Materials
Compact-type (CT) fatigue crack growth (FCG) specimens have been prepared from single crystals of SRR99. The macroscopic crack planes {l_brace}hkl{r_brace} and propagation directions were (110)[{bar 1}10], (110)[{bar 1}11], (110)[001], (111)[1{bar 1}0], and (001)[010]. FCG tests were conducted at 650 and 850C in air at 10 and 1 Hz at an R ratio of 0.1. At 650 C, (110) and (111) specimens showed a frequency-dependent FCG rate, not apparent for (001)[010], due to increased cuboidal cross-slip and reduced reversibility at lower frequency. Slip homogenization at 850 C prevented this effect. (001)[010] demonstrated a lower Paris regime FCG rate at 850 C than at 650 C due to crack bifurcation at the higher temperature. Conversely, a higher FCG rate occurred for (110) and (111) specimens at 850 C, as crack tortuosity decreased as it changed from propagation along the {gamma}/{gamma}{prime} interface at 650 C to precipitate cutting at 850 C. An orientation-dependent FCG rate and fracture path was found. At 650 C orientations able to accommodate crack tip shear on primary slip planes near-parallel with the crack front provided the best FCG resistance. At 850 C the best FCG response was found for the same orientations that now developed large scale ridges as a result of out-of-plane cuboidal slip.
- OSTI ID:
- 271697
- Journal Information:
- Acta Materialia, Journal Name: Acta Materialia Journal Issue: 1 Vol. 44; ISSN XZ504Y; ISSN 1359-6454
- Country of Publication:
- United States
- Language:
- English
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