Preparation And Radiation Tolerance Of YSZ/Al₂O₃ Multilayered Nanofilms With Pre-existing Nanovoids And Nanochannel Al_0.1FeCoNiCr High-entropy Alloy Films

Nuclear materials for the future advanced nuclear reactor system will be subjected to higher temperatures and higher neutron doses well beyond those of current reactors.The interaction of fast neutron with materials not only leads to the formation of point defects,but also produces great amounts of transmuted gas atoms.These point defects and gas atoms can further combine into defect clusters and bubbles.The irradiation-induced microstructure evolution and mechanical property degradation of nuclear materials,as evidenced by void swelling,hardening and embrittlement,can be significant obvious,or even ultimately leads to the failure of materials.Thus,the development of novel materials with enhanced radiation tolerance is of great significance.Recently,the strategy of incorporating high-density grain boundaries or heterophase layer interfaces,such as nanocrystalline or nanolayer materials,as defect sinks to enhance radiation damage tolerance of materials has been investigated intensively.However,plenty of research show that although such grain boundaries or interfaces can significantly enhance the radiation damage resistance of materials,their radiation damage tolerance remain limited.At very high irradiation doses the main mechanism leading to failure in nanostructured materials are defects and transmuted gas atoms which may migrate to grain boundaries or interfaces and form cavities or bubbles.Therefore,lead to the formation of cracks.First,the utilization of high density small sinks to collect the defects and transmuted gas atoms away from interfaces and to prevent the formation of large cracks might be a potential strategy for designing of nanostructured materials with much higher resistance to radiation-induced embrittlement.Besides,intentionally incorporated free surface in nanostructured materials to annihilate defects and to release transmuted gas atoms also can suppress the formation of large cavities（voids and bubbles）and cracks.Therefore,the research and development of novel nanostructured materials with high radiation tolerance is an important task in the future advanced nuclear reactor system research.To preserve the physical properties,minimizing dimension of defects and reducing number of defects are particularly important in the thin film growth.However,intentionally incorporating defects in thin films can manipulate the properties of the films.In this work,we report YSZ/Al₂O₃ multilayered nanofilms with pre-existing nanovoids and nanochannel Al_0.1Co Cr Fe Ni high-entropy alloy films.The effect of He or Ke ion irradiation and the nanostructure on mechanical properties were studied respectively.Detailed contents include the following:1)By optimizing the magnetron sputtering deposition parameters,the YSZ/Al₂O₃ multilayered nanofilms with pre-existing nanovoids were successfully prepared.At room temperature,the nanofilms were irradiated by He⁺ions to different fluences at room temperature.The He bubble formation and evolution in the YSZ/Al₂O₃ multilayered nanofilms with pre-existing nanovoids were analysed by transmission electron microscope（TEM）and it was found that the He atoms can be captured and stored by the pre-existing nanovoids,and the growth of He bubbles was restricted inside the Al₂O₃ layers to avoid the formation of large bubbles.In addition,the hardness and Young’s modulus of the YSZ/Al₂O₃ multilayered nanofilms were analysed by nanoindentation.Radiation-induced softening and improved wear resistance were observed in the YSZ/Al₂O₃ multilayered nanofilms irradiated to high fluences of He⁺ions.The enhanced radiation tolerance and improved mechanical properties of the YSZ/Al₂O₃ multilayered nanofilms with pre-existing nanovoids were attributed to the interaction between interfaces and nanovoids through“loading-unloading”effect.2)Several nanochannel Al_0.1Co Cr Fe Ni high-entropy alloy films with different morphology were successfully prepared by magnetron sputtering deposition.The influence of various experimental parameters on the film morphology of these nanochannel Al_0.1Co Cr Fe Ni high-entropy alloy films were investigated,such as working pressure and substrate temperature.This work presents an investigation into the irradiation tolerance and the mechanical response of the Al_0.1Co Cr Fe Ni high-entropy alloy film irradiated by 800 ke V Kr²⁺ions to a fluence of 1×10¹⁶ ions/cm²（peak damage,22.5 dpa）or irradiated by 40 ke V He⁺ions to a fluence of 5×10¹⁷ ions/cm²（peak He concentration,41.2 at.%）.We found that the Al_0.1Co Cr Fe Ni high-entropy alloy film exhibits better radiation damage tolerance and He management ability than its dense counterpart.Furthermore,nanoindentation tests show that the irradiated Al_0.1Co Cr Fe Ni high-entropy alloy film also has an enhanced mechanical response compared with its dense counterpart:（1）for the Kr²⁺ion irradiation,the strain rate sensitivity（SRS）of the Al_0.1Co Cr Fe Ni high-entropy alloy film has only a slight decrease compared with a large decrease for the dense counterpart;and（2）the SRS exponent（m）of the Al_0.1Co Cr Fe Ni high-entropy alloy film doubles after He⁺ion irradiation,while that of the dense counterpart varied from positive to negative.These results highlight that nanochannel structures with enormous free surface can mitigate the deleterious effects of irradiation compared with its dense counterpart,and represents a promising new way for making radiation-tolerant materials for the advanced nuclear reactor systems.