Screening of the mechanical stability of M₂AX phases for nuclear applications

In the present work, we apply a high-throughput density functional theory (DFT) screening of interesting M₂AX phase compounds for nuclear applications by assessing their mechanical stability. Evaluation of mechanical stability allows to assess thermodynamically unstable phases and does not require the assessment of competing MX and intermetallic phases. We consider all possible combinations with M = {Ti, Cr, Zr, Nb}, A = {Al, Si, Sn, Pb, Bi} and X = {C}, including “out-of-plane” ordering that is so far unobserved in M₂AX phases. For all fifty possible combinations, we determine the elastic constants and verify their mechanical stability. In addition, for each combination, the free surface energy is computed and the fracture toughness, K_ic , is determined. The results are discussed in terms of combinations with high mechanical stability and high K_ic. Apart from suggestions of interesting new combinations, the results also form the basis for any plasticity or fracture mechanics model for these MAX phases.