L12-type Ni3Al-based high-entropy aluminides with superior strength-ductility: From design to criteria

L1₂-type Ni₃Al-based high-entropy aluminides (HEAs) with superior strength-ductility synergy exhibit great potential as advanced structural materials. Nevertheless, effective design method and phase formation criteria applicable to L1₂-type Ni₃Al-based HEAs remain elusive. In this study, the design method of L1₂-type Ni₃Al-based HEAs was systematically discussed from site preference of atoms, selection of multi-principal elements to determination of stoichiometric ratio. A series of L1₂-type Ni₃Al-based HEAs with excellent mechanical properties were successfully developed using this design strategy, and corresponding phase formation criteria were proposed. The designed alloys exhibited a high volume fraction of ordered L1₂ phase (>75 %) and a small amount of disordered FCC phase. The as-cast HEAs-1 alloy showed excellent high yield strength (>600 MPa) and ultimate tensile strength (>1200 MPa) with large tensile elongation (>35 %). Moreover, a new thermodynamic parameter, enthalpy-entropy ratio $\eta$, was established based on the pseudo-binary sublattice model. The formation of L1₂-type Ni₃Al-based HEAs is conducive within the ranges of $\eta \ge 1.1$, ${\delta }_r^{\ast }<3\%$, $4.5\%<{\delta }_r^{A-B}<6.5\%$, $\Delta {\chi }^{\ast }<5.5\%$, $6\%<\Delta {\chi }^{A-B}<9.5\%$, ${\sigma }_{VEC}^{\ast }<1.1$, $2<{\sigma }_{VEC}^{A-B}<3$, and $8<VE{C}_{tot}<8.5$. The correctness and validity of the phase formation criteria were verified through the designed experiments. The criteria are simple and reliable, and can provide method and guidance for designing and developing advanced structural materials with superior mechanical properties.