First-principles study of the mixing effects of rare earth solute atoms on the physical properties of Al₂RE phases in Al-based alloys at finite temperatures

Abstract

The structural stability, mechanical properties, internal nucleation and growth mechanisms, and surface energies of Al2RE (RE=Sc, Y, La-Lu) second phases in Al alloys have been investigated by combining first-principles calculations with the Debye model. The results show that the lattice mismatch of Al2RE precipitates with Al matrix, which determines the strength of materials associated with dislocation slips, are closely related to the transferred electron et between Al and RE atoms. Furthermore, the methods of cluster expansion (CE) and special quasi-random structures (SQS) have been adopted to calculate the mixing enthalpy Hx of Al2RE11-xRE2x (RE1=La, Ce, Pr, Nd; RE2 is the rest RE atoms) for studying the possibility of replacing in the Al2RE (RE=La, Ce, Pr, Nd) compounds, which is explored in experiments, and it is found that the mixing enthalpy Hx increases with the substitute concentration. The calculated elastic constant Cij, bulk modulus B, shear modulus G, Young’s modulus E decrease with increasing atomic number from Sc to Y at first, and then increases to Lu; while the Cauchy pressure C12-C44 and pugh’s ratio B/G show the opposite trends. Moreover, the critical nucleation radius R* and coarsening rate KLSW of Al2RE are obtained from the classical nucleation theory (CNT) and LSW model, respectively. The results show that, the R* for all interfaces decreases from Y to La at first, and then increases linearly to Lu; whereas the KLSW of all models increases from Y to Ce firstly, and then changes very little. Finally, the calculated surface energy Esur of all Al2RE compounds is much higher than that of Al, and with the increase of atomic number, Esur of Al2RE intermetallic compounds decreases firstly from Sc to La, and then increases to Lu. The result is helpful for the further optimal designing high performance of Al alloys.