Deformation modes and yield strength anomaly in L12 compounds

Abstract

The synergy between various planar fault energies coupled with elastic anisotropy plays a major role in determining the deformation modes and thereby the yield strength anomaly in superalloys. The present work focuses on the feasibility of using planar fault energies and elastic moduli derived from density functional theory calculations and predicting thermodynamic viability of yield strength anomaly for elastically anisotropic compounds. Fault energies and elastic moduli in different binary (A₃B) and pseudo-binary Ni₃Al_(1−x)C_x (C=Ta, Ti, and Ni) systems were estimated. It was observed that the alloying has a non-monotonic effect on the trends in fault energies and elastic moduli in Ni₃Al_(1−x)C_x. The addition of Ta and Ti to Ni₃Al reduced the activation energy for cross-slip while Ni has the opposite effect. These predictions corroborate with the experimental results from literature that the peak shifts to lower temperatures in flow stress vs temperature curve. It was concluded that alloying elements that primarily affect fault energies influence yield anomaly in Ni₃Al_(1−x)C_x. Maps depicting the criteria for yield strength anomaly were developed for various combinations of critical fault energy ratios and elastic anisotropy. These results were discussed in the purview of alloy design and guidelines for screening complex precipitates compositions were proposed.