Influence of the crystallographic orientation of FCC single crystals on plastic strain under uniaxial monotonic and cyclic thermomechanical loading

Single-crystal superalloys, used in production of gas turbine blades, have a pronounced anisotropy of mechanical properties and high short-term, long-term and thermal fatigue strength. Based on a microstructural model of elastoplastic deformation, which takes into account the presence of octahedral and cubic slip systems, a study was carried out of the influence of the crystallographic orientation of single-crystal samples on the level of plastic strain under uniaxial tension and on the range of plastic strain under intense thermal cycling. Anisotropy of the plastic properties of single crystals manifests itself in the dependence of the level of plastic strain on the direction of loading. The contribution of octahedral and cubic slip systems under uniaxial loading in different directions with respect to the crystal lattice has been evaluated. The evolution of the spatial orientation of plastic strain with a monotonic increasing of loading has been studied; the initiation and competing growth of local maxima have been analyzed. The angular coordinates of all possible 7 local maxima within the stereographic triangle are found and the load ranges of their dominance are indicated. The results of studying the influence of temperature and hardening on the orientation distribution of plastic strain are presented. The influence of the sample crystallographic orientation on the plastic strain level under symmetric and nonsymmetric cyclic loading has been studied. The results of modeling the cycle-by-cycle kinetics of plastic strains and their orientation distribution are presented. The results of the computational experiments for corset samples for thermal fatigue tests showed a significant sensitivity of the plastic strain range to the deviation of the sample axis from the [001] orientation even by a few degrees, which indicates the need to revise the accepted tolerance of 10 degrees.