Investigating the effects of phosphorus in a binary-phase TiAl-Ti₃Al alloy by first-principles: from site preference, interfacial energetics to mechanical properties

We investigate the site preference of phosphorus (P) and its effects on the mechanicalproperties of the binary phase TiAl-Ti₃Al alloy using a first-principles method in combinationwith empirical criterions. We show that P is energetically sitting at the substitutionalAl site in the Ti₃Al layer of the TiAl/Ti₃Al interface, which can beunderstood from the difference of electronegativity between P and Ti/Al. Both the cleavageenergy (γ_cl) and the unstablestacking fault energy (γ_us) decrease withthe presence of P, which indicates the strength of the TiAl/Ti₃Al interface will be weaker andthe mobility of the dislocation will be easier induced by P. Further, we demonstrate thatthe ratio of γ_cl/γ_usof TiAl/Ti₃Alinterface with P is 5.03, 0.19% lower than that of the clean TiAl/Ti₃Al interface, suggesting thatthe P impurity will slightly reduce the ductility of the TiAl/Ti₃Al interface.