The Microstructure And Properties Of V₂ALC Coating Prepared By Magnetron Sputtering

The accidents at the Fukushima Daiichi Nuclear Power Plant at the beginning of this century have led to a reappraisal of the traditional Zr-based alloy cladding system for current light water reactors.Considering the large numbers of operating Zr-UO₂fuel system and the lack of practical operating experience of alternative fuel claddings and fuel pellets,the modification of current Zr-based alloy claddings through surface modification by coating is a more reliable and cost-efficient way to improve the safety of ATF systems,M_n+1AX_n phases,where M is an early transition metal?mostly groups 13 and 14?,A is an A-group element and X is either C and/or N,is desired for technological nuclear applications due to their high-temperature resistance to corrosion and unusual irradiation damage-tolerance.However,as previous studies,most of the MAX-phase coating were prepared on single-crystal substrates in high temperature.For coating application of crystalline MAX phases onto suitable nuclear cladding materials?such as Zr alloys?,the non-epitaxial vapor deposition of crystalline MAX coatings on amorphous substrates?for example glass or SiO₂?is necessary.The evaluation to the irradiation damage-tolerance and mechanical properties also have a great significance to MAX-phase coating for the nuclear application.In this study,V₂AlC was chosen as the coating material,the main findings and conclusion are as follows:i.Preparation:the one step synthesis of crystalline V₂AlC on amorphous substrates.we prepared films on different substrates by sputter-deposition at a relatively low temperature.the?110?texture V₂AlC coatings were achieved with microstructural optimization after the detail research on the preparation parameters.Characterized by Rutherford backscattering spectrometry,X-ray diffraction,Raman spectroscopy,and transmission electron microscopy,etc.we found the near-stoichiometric films were mainly composed of the V₂AlC crystalline phase.ii.Growth microstructure:we observed the initial nucleation process of randomly oriented V₂AlC grain occurred at the amorphous-substrate/film interface.Accordingly,the competitive growth evolution of?110?plane characterized by Rutherford backscattering spectrometry,X-ray diffraction,Raman spectroscopy,and transmission electron microscopy.High content of crystalline V₂AlC phase was obtained in films with nearly stoichiometric composition.The microstructural evolution includes random nucleation at the film/substrate interface and competitive growth which results in a?110?preferred orientation with increasing thickness.iii.Irradiation resistance:the irradiation damage-tolerance evaluation to V₂AlC-Zr systems.The as deposited V₂AlC-Zr systems were irradiated with different doses of He ions at room temperature,and annealing was performed after the irradiation.The irradiated V₂AlC-Zr systems was characterized by TEM to analyze the behavior of He atoms and the formation of He bubbles.The He bubbles along the interface were larger and denser than the bubbles on the Zr substrate and coating.It further demonstrated that the interface between the substrate and coating were the preferential nucleation sites for the He bubbles.iv.Mechanical properties:the relationship of the adhesion of V₂AlC coatings ith He ions doses are studied with the scratch tests.The adhesion of the coating decreased under irradiation conditions and with increasing irradiation dose.In conclusion,we have demonstrated that the fully crystalline V₂AlC could be directly achieved on amorphous substrates by magnetron co-sputtering.The mechanical behavior of the V₂AlC coatings changes with the irradiation doses.The results contribute to the MAX phases coatings in low-temperature preparation and nuclear applications on cladding material for ATFs.Based on this study,the further research could be conducted on the corrosion behavior in steam at high temperature,physical?optical and electrical?properties,and the preparation of related MXenes materials.