Prediction of yield strength anomaly by improved semi-discrete variation Peierls-Nabarro model for L12-ordered alloys Ni3X and Co3X

Nickel-based and Cobalt-based superalloys (NBSA and CBSA) are widely used in hot-end components of aero engines for their excellent mechanical properties and special microstructures with both γ and γ’ phases. The γ’ phase exhibits a yield strength anomaly (YSA, i.e., the yield strength increases with the increase of temperature), which can significantly affect the overall mechanical behavior of superalloys. To investigate the necessary conditions for the generation of YSA in these L1₂-ordered NBSAs and CBSAs, the commonly used PPV model is improved with special consideration of the potential type I’ superdislocation core structure, and the related parameters and physical properties of superdislocations are achieved by the enhanced SVPN model including the lattice discreteness effect and by the DFT calculations. It is found that there are three possible superdislocation core structures (i.e., type I, type I’ and type II), but the type I’ core structure has the lowest total energy, and thus the formation of type I’ superdislocation configuration is the most energetically favorable at least when external loading is applied. For this, the influence of type I’ superdislocation on the generation of YSA behavior should be given special consideration. In addition, the energetically favorable type I’ configuration also exhibits the lowest predicted Peierls stress. Further, if the classical PPV model without considering the type I’ configuration is employed, it may give a wrong prediction for the YSA behavior of Ni₃Al, Ni₃Ga, Ni₃Si, Ni₃Ge and Co₃Al_0.5W_0.5. However, by the present improved PPV model, predictions consistent with the experimental observation can be obtained. Consequently, the consideration of type I’ configuration in the present improved PPV model and the employment of enhanced SVPN model with lattice discreteness effect are necessary and appropriate.