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Carbides for Future Fission Environments (MAX Phases)

P. D. Bristowe, S. H. Shah and S. Azadi

Sponsors: EPSRC

  • First principles modelling of the phase stability of MAX phases, Zrn+1ACn, (A = S, Al, Sn, Pb; n = 1, 2)
  • Irradiation tolerance of MAX phases and their resistance to amorphization
  • Strength of grain boundaries and other interfaces in MAX-phase systems
  • Collaboration between Cambridge, Imperial College and Manchester University involving support from Westinghouse, National Nuclear Laboratory and Rolls-Royce plc.

Research Highlight

Point defect formation in M2AlC (M = Zr, Cr) MAX phases and their tendency to disorder and amorphize

S. H. Shah and P. D. Bristowe, Sci. Rep. 7, 9667 (2017)

First principles calculations are performed on Zr2AlC and Cr2AlC MAX phases to compare their ability to accommodate point defects under irradiation. Interatomic bonding is stronger in Cr2AlC than Zr2AlC but contrary to expectation Zr2AlC exhibits higher vacancy and antisite pair formation energies. However, interstitials and Frenkel defects are generally more difficult to form in Cr2AlC. The results are attributed to the mixed covalent/ionic/metallic nature of the bonding. Detailed comparison of all the energies suggests that the preferred defects in Zr2AlC and Cr2AlC are the VAl+Ali Frenkel and CrAl+AlCr antisite respectively. Thus the potential response of the two phases to irradiation is different and taking account of other competing defects it is suggested that Zr2AlC is less susceptible to amorphization. 

MAX phase image

 

Formation energies (Edefect) of different point defects in Zr2AlC and Cr2AlC. Here M is Zr/Cr. (a) vacancy defects, (b) antisite pair defects, (c) different interstitial configurations (I), (d) interstitial defects. For the vacancies and interstitials the chemical potentials of the pure constituent elements are used.