Tension-compression asymmetry of the (001) single crystal nickel base superalloy SC16 under cyclic loading at elevated temperatures
- Bundesanstalt fuer Materialforschung und -pruefung, Berlin (Germany). Laboratorium V.13-Elektronenmikroskopie
Fully reversed low cycle fatigue tests were conducted on <001> oriented single crystals of the nickel base superalloy SC16 at a constant total strain range of 2.0%. The strain rates were varied from 10{sup {minus}2} to 10{sup {minus}5} s{sup {minus}1} at 750 C and the temperatures were changed from 650 to 950 C under the strain rate 10{sup {minus}3} s{sup {minus}1}. During cycling under the high strain rates 10{sup {minus}2} and 10{sup {minus}3} s{sup {minus}1} at 750 C or under the strain rate 10{sup {minus}3} s{sup {minus}1} at 650 C, the SC6 single crystals show that the tensile stress (T) is higher than the compressive stress (C). During cycling under the low strain rates 10{sup {minus}4} and 10{sup {minus}5} s{sup {minus}1} at 750 C or under the strain rate 10{sup {minus}3} s{sup {minus}1} at 850 C, the cyclic tension-compression asymmetry of C > T was observed. At 950 C under the strain rate 10{sup {minus}3} s{sup {minus}1}, no tension-compression asymmetry (T = C) was present during fatigue testing. The deformation mechanism corresponding to T > C determined by transmission electron microscopy (TEM) is that the {gamma}{prime} precipitates are sheared by pairs of a/2<110> matrix dislocations coupled by antiphase boundaries (APB) within {gamma}{prime} phase. The reversed asymmetry behavior (C > T) was found to be associated with the (111)<112> viscous slip producing superlattice intrinsic/extrinsic stacking faults (SISF/SESF) in {gamma}{prime} precipitates. At 950 C (T = C) dislocation climbing over the {gamma}{prime} precipitates becomes the dominant deformation mechanism. Models which can explain the tension-compression asymmetry behavior were discussed.
- OSTI ID:
- 415393
- Journal Information:
- Acta Materialia, Vol. 44, Issue 10; Other Information: PBD: Oct 1996
- Country of Publication:
- United States
- Language:
- English
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