Cyclic softening and hardening behavior of a nickel-base superalloy

The cyclic stress response of directionally solidified Mar-M247LC superalloy is investigated as a function of test temperature and gamma-prime particle size. The role of dislocation behavior in the cyclic hardening and softening of this alloy is also discussed. In the gamma-prime specimen cyclic softening occurs at 760 C and cyclic hardening is observed at 871 and 982 C. On the other hand, cyclic hardening is observed in the 1.0 mm gamma-prime specimen at 760 C. Cyclic softening is associated with the shearing of gamma-prime particles by dislocations and cyclic hardening is associated with the Orowan looping of dislocations around the gamma-prime particles. (AIAA)