An analysis of yield phenomena in Rene N4+ single crystals with respect to orientation and temperature.

摘要

Tensile, double-tensile, and low cycle fatigue mechanical testing was done on single crystals of the nickel-base superalloy Rene N4+. The crystals were of five different nominal orientations: (001), (011), (012), (;The tests above the peak temperature showed a strain rate sensitivity for the yield stress, as expected from previous research. The tests below the peak temperature, however, were dramatically different, with the general shape of the stress-strain curve quite different for the different orientations. Some orientations exhibited serrated yielding, some had substantial strain relaxation during the hold time of double-tensile tests, some strain hardened, and some had combinations of the previous behaviors.;The dislocation structures observed for the different orientations corresponded well with the observed yield phenomena. Cube cross-slip was present when there was serrated yielding. Multiple primary octahedral slip or very difficult dube cross-slip was present when there was strain relaxation. Primary cube slip or very difficult cube cross-slip was present when there was strain hardening. For tests above the peak temperature there were stacking faults in all samples with primary octahedral slip.