Crystal Plasticity Study of Heterogeneous Deformation Behavior in γ Matrix Channels during High Temperature Low Stress Creep of Single Crystal Superalloys

TL;DR: In this paper, a sine-hyperbolic-based material creep model was used for the matrix, while the precipitates are assumed to be elastic and a softening model incorporating the evolution of mobile dislocation density was used to capture the transition from secondary to tertiary creep.

Abstract: Single crystal nickel-based superalloys have high temperature creep resistance due to particle strengthening by high volume fraction of coherent γ′ precipitates distributed within nickel-based solid solution γ matrix. In the high temperature low stress regime, published experimental studies reveal that the creep deformation mechanism during the secondary stage is predominantly by dislocation glide in the γ matrix only, and that there is a preferential motion of dislocations in the matrix, oriented in a direction perpendicular to the stress. In this work, the crystal plasticity finite element method is employed to perform creep simulations on a representative volume element in the high temperature and low stress regime. A sine-hyperbolic–based material creep model was used for the matrix, while the precipitates are assumed to be elastic. A softening model incorporating the evolution of mobile dislocation density was used to capture the transition from secondary to tertiary creep. The predicted creep curves agree well with the published experimental measurements on single crystal superalloy CMSX-4. The simulations predict a higher creep strain distribution in the horizontal channel of the matrix (perpendicular to the applied stress) as compared with the vertical channel (horizontal to the applied stress). Local creep strain distributions in the channels were found to be greater than twice their average creep strain. The results provide key insights into the distribution of macroscopic creep strain in the local channels of the γ matrix to further aid in the microstructural design of creep-resistant superalloys.