Atomic-scale unveiling of strengthening in interstitial solid soluted Nb-rich TiAl alloys

Understanding interaction between interstitial elements and matrix at the bulk phases and phase interfaces is crucial in alloy design. In this study, using first-principles density functional theory, we investigate the effect of interstitial elements (B, N, and C) on electronic structures and elastic properties for the primary γ-TiAl and α₂-Ti₃Al phases of TiAl alloys. It shows that N has the highest solid solubility than B and C based on the calculation of energy and corresponding experimental results, implying that it has the strongest interaction with the matrix simultaneously. The Cottrell atmosphere induced by interstitial elements can be intensified by increasing the bonding strength as it would significantly improve the strength of the alloys. The N element would increase the interfacial separation energy, strengthen the interfaces, facilitate dislocation pile-ups, and finally strengthen the interfaces of TiAl alloys. Moreover, the N element also enhances the toughness of the phase to the highest degree according to B/G. For Nb-rich TiAl alloys, Nb promoting the formation of Ti anti-site sites can facilitate solid solubility of interstitial elements and strengthen their bond with the nearest adjacent atoms in the matrix. The theoretical results were further confirmed by experiments.