Radiation resistance and mechanical properties of magnetron-sputtered Cr₂AlC thin films

Cr₂AlC MAX phases were deposited using magnetron sputtering. The synthesis was performed via layer-by-layer deposition from elemental targets onto Si wafer and polished Inconel® 718 superalloy substrates at 650 K and 853 K. Transmission Electron Microscopy (TEM) characterisation showed that the thin films had a thickness of about 0.8 and 1.2 m for Si and Inconel® substrates, respectively, and a MAX phase crystalline structure. Depositions onto Inconel substrate was performed in order to measure film mechanical properties. The films have hardness at around 15 GPa, reduced Young’s modulus at around 260 GPa, do not delaminate and showed characteristic ductile behaviour during nanoscratching. Ion irradiations with in situ TEM were performed with 320 keV Xe+ ions up to fluence 1×1016 ions·cm-2 at 300 K and 623 K. At 300 K the Cr₂AlC started to amorphise at around 0.3 dpa. At displacement levels above 3.3 dpa all crystalline structure was almost completely lost. Conversely, irradiations at 623 K showed no recordable amorphisation up to 90 dpa. It is discussed that the presence of many grain boundaries and low defect recombination energy barriers are responsible for high radiation hardness of Cr₂AlC MAX phase at 623 K. The thin film Cr₂AlC MAX phases have mechanical and radiation stability which makes them a candidate for fuel rod coating as Accident Tolerant Fuels (ATF) material for the next generation of nuclear reactors.