On the relationship between anisotropic yield strength and internal stresses in single crystal superalloys

The present work focuses on the cubic slip phenomenon in single crystal superalloys with a high fraction of γ′ precipitates at high temperature.The macroscopically apparent cubic slip mechanism is known to significantly reduce the tensile and creep strength of 〈1 1 1〉 oriented specimens. However, recent results obtained by 3D dislocation dynamics (Vattré et al., 2009) suggest a new interpretation of the so-called pseudo-cubic slip related to the nature of the dislocation network formation at the interfaces. These results are taken into account in a micromechanical model to improve the estimation of the strain hardening anisotropy. In accordance with the discrete simulations, it is shown that a key role is played by the combination of the activated octahedral slip systems as a function of the crystal orientation. In the 〈1 1 1〉 case, the contribution of the activated systems to kinematical hardening compensate, whereas strain hardening remains high for the 〈0 0 1〉 case. The experimental dependence of plastic flow on the orientation is also explained at the dislocation-scale mechanisms.Results are presented for the alloy CMSX-4 in several orientations.