The stability of irradiation-induced defects in Zr₃AlC₂, Nb₄AlC₃ and (Zr_0.5,Ti_0.5)₃AlC₂ MAX phase-based ceramics

This work is a first assessment of the radiation tolerance of the nanolayered ternary carbides (MAX phases), Zr₃AlC₂, Nb₄AlC₃ and (Zr_0.5,Ti_0.5)₃AlC₂, using proton irradiation followed by post-irradiation examination based primarily on x-ray diffraction analysis. These specific MAX phase compounds are being evaluated as candidate coating materials for fuel cladding applications in advanced nuclear reactor systems. The aim of using a MAX phase coating is to protect the substrate fuel cladding material from corrosion damage during its exposure to the primary coolant. Proton irradiation was used in this study as a surrogate for neutron irradiation in order to introduce radiation damage into these ceramics at reactor-relevant temperatures. The post-irradiation examination of these materials revealed that the Zr-based 312-MAX phases, Zr₃AlC₂ and (Zr_0.5,Ti_0.5)₃AlC₂ have a superior ability for defect-recovery above 400 °C, whilst the Nb₄AlC₃ does not demonstrate any appreciable defect recovery below 600 °C. Density functional theory calculations have demonstrated that the structural differences between the 312 and 413-MAX phase structures govern the variation of the irradiation tolerance of these materials.