Size effects of γ′ precipitate on the creep properties of directionally solidified nickel-base super-alloys at middle temperature

Nickel-base super-alloys consist of two phases named γ-phase of nickel matrix and γ′-phase of precipitates, which are dispersed uniformly in the matrix. The morphologies and sizes of γ′ precipitates have strong effects on the creep properties of the alloys. At the middle temperature (850 °C), the rafting effect of the precipitate is not obvious, and the size effects of precipitates are dominant. In this paper, a crystal plasticity constitutive model is developed, which considers damage and strain gradient to reflect the size effect of the creep property. This model is implemented into ABAQUS as an interface of user material (UMAT). Two different precipitate sizes are studied using a unit-cell model of alloys with the same volume fraction. By Comparison with the experiment data, the simulation results are reasonable to demonstrate the significant size effect of precipitates on the creep properties of nickel-base super-alloys, which indicates that the creep rates are lower and the rupture lives are longer when the precipitate sizes are smaller with constant fraction.