Numerical study of the flow responses and the geometric constraint effects in Ni-base two-phase single crystals using strain gradient plasticity

The [001] tensile flow of a single-crystal superalloy (CMSX-4) having a high volume fraction of regularly-arrayed cuboidal gamma' precipitates was simulated using a gradient-dependent plasticity model for the constitutive description of the gamma-matrix. The simulated flow curves showed flow softening in the early stage of straining. Flow softening was accompanied by the organized catastrophic plastic flow of the gamma-matrix, which resulted from the breakdown of the geometric (or kinematic) constraints imposed by the gamma/gamma' microstructure. The flow-softening behavior was influenced by the thickness of gamma-matrix channels (a volume fraction of the gamma' precipitates), the flow property of the gamma-matrix and the geometry of the gamma'-precipitate edge. In particular, changing the radius of the gamma'-precipitate edge resulted in a dramatic variations in the flow curves. The present unit-cell simulations exhibited good predictions for the gamma'-precipitate size dependence of the flow stress at moderate strains. (c) 2005 Elsevier B.V. All rights reserved.