Mesoscale cyclic crystal plasticity with dislocation substructures

An advanced constitutive model incorporating two specific aspects of Ni-base superalloy deformation behaviour is proposed. Several deformation mechanisms are active in these two-phase materials. In the matrix phase, cube slip plays an important role in the orientation dependence of the material. Moreover, inelastic deformation of the precipitate phase leads to non-Schmid effects in the material response. Macroscopic cube slip is modelled here by incorporating a zig-zag cross slip mechanism into the constitutive relations for the matrix phase. A cross slip factor is proposed that quantifies the amount of cross slip and consequently represents the orientation dependence of the cube slip. Further, a detailed precipitate phase constitutive model is proposed, which enables the simulation of non-Schmid effects, like the tension–compression asymmetry. The cross slip mechanism and the associated splitting of partial dislocations in the γ'-phase, which are responsible for the anomalous yield behaviour, are incorporated in the model. The proposed formulations are implemented in a recently developed crystal plasticity framework for single crystal Ni-base superalloys and a consistent set of model parameters for the commercial alloy CMSX-4 is determined. The model is shown to reasonably predict the material tensile response and creep behaviour for a range of temperatures and stress or strain rate levels. The incorporation of the cross slip mechanisms in the matrix and precipitate results in an adequate simulation of the material orientation dependence and the experimentally determined tension–compression asymmetry.

https://iopscience.iop.org/article/10.1088/0965-0393/18/1/015005/pdf

Cube slip and non-Schmid effects in single crystal Ni-base superalloys

A multiscale model for the elastoviscoplastic behavior of Directionally Solidified alloys: Application to FE structural computations

The influences of applied stress (120–760 MPa) and temperature (700–1000 °C) on the creep deformation mechanisms of the newly developed nickel-base superalloy M951G have been studied. The dominant deformation mechanisms of M951G alloy after different creep tests were systematically investigated and the reasons for their transition were well discussed. A creep mechanism map at various creep conditions was summarized and the theoretical critical resolved shear stresses (CRSSs) of various creep mechanisms under different temperatures were also calculated. Results show that the CRSSs of different creep mechanisms display different dependencies of temperature and the favorable deformation mechanisms at different creep conditions are different. τ APB , τ OB and τ CL are decreased to varying degrees with the temperature increasing; on the contrary, there is a positive correlation between τ SF and temperature. At low temperature region, the favorable deformation mechanism is shearing of γ′ precipitates by stacking faults. However, it changes to antiphase boundaries (APBs) coupled dislocation pairs shearing in the γ′ precipitates and dislocation climbing in the γ matrix channel at high temperatures. At intermediate temperatures, both stacking faults and APBs are observed owing to the alternate leading of the CRSSs for APBs and stacking faults shearing in γ′ precipitates.

H.C Yang

Papers

Deformation mechanism for high temperature creep of a directionally solidified nickel-base superalloy