Dynamic recrystallization of grains during creep deformation of alloy 690 at 800–1000 °C

Abstract

This study reports the dynamic recrystallization behaviour of alloy 690 during creep at 800 to 1000 °C. Creep tests were conducted at stresses ranging from 25 to 105 MPa, which corresponded to about 0.4 to 0.7 of the yield strengths at respective temperatures. Crept samples failed by necking or cavitation depending upon the creep test conditions. The necking dominated at lower temperatures and lower stress levels, whereas the cavitation dominated at higher temperatures and high stress levels. Extensive dynamic recrystallization of grains was observed in samples dominated by necking as the failure involved deformation of grains. In contrast, cavitation dominated samples exhibited limited dynamic recrystallization of grains. At intermediate temperatures and stresses, the dynamic recrystallization of grains was less significant as the failure was due to the co-existence of necking and cavitation type fracture. The size of the recrystallized grains was inversely related to the applied stress, in agreement with the literature. Discontinuous dynamic recrystallization of grains was found to be the mechanism responsible for the formation of dynamically recrystallized grains in the present study. • Dynamic recrystallization of grains has been observed during creep deformation of Alloy 690. • The alloy fails by (i) necking (at low-temperature and low-stress) or (ii) cavitation (high-temperatures and high-stresses) during creep at 800–1000 °C. • Only samples that failed by necking exhibited dynamic recrystallization of grains, whereas samples that failed by cavitation exhibited negligible dynamic recrystallization. • Discontinuous dynamic recrystallization was found to be the dominant dynamic recrystallization mechanism in the present study.