Study On The Preparation And Radiation Resistance Of SiC Whiskers Toughened Al₂O₃ Matrix Composite Ceramics

Zirconia toughened alumina(ZTA)composites is considered as one of the candidate materials for nuclear energy devices due to its excellent mechanical properties.Although the toughness of ZTA composites is improved by phase transformation toughening,it still cannot meet the requirements of structural materials for nuclear energy devices.To be used in the nuclear energy field,composites need not only excellent mechanical properties,but also high thermal conductivity,strong corrosion resistance,good radiation resistance and thermal stability,among which the radiation resistance is crucial to the safety of nuclear energy system.Therefore,it is of great significance to further study the performance improvement and irradiation resistance of ZTA composites for the research and development of high-performance ZTA matrix composites for nuclear energy installations.In this thesis,ZTA/Al₂O₃-Si C_w composites were prepared by spark plasma sintering(SPS)method with zirconia toughened alumina ceramics as the matrix,Al₂O₃ceramics as the contrast and Si C whiskers(Si C_w)as the toughening phase.The amount of Si C whiskers was 3.0,5.0,7.0 and 10.0 vol%,respectively.The effect of adding small amount of whiskers on the microstructure and properties of ZTA/Al₂O₃-Si C_wcomposites were studied by testing the phase structure,microstructure,mechanical and thermal properties.The radiation resistance of ZTA/Al₂O₃-Si C_w composites was studied by He/Si ion irradiation technique,which provided experimental basis for nuclear energy application of Si C_w toughened alumina matrix composite ceramics.The innovative results of this paper are summarized as follows:1.ZTA-Si C_w composites:With the increase of the content of Si C whiskers,the density of the composite material first decreases and then increases,and the average grain size gradually decreases,which indicates that the addition of silicon carbide whiskers has the effect of refining grains.The flexural strength of composite ceramics increases with the increase of whisker content.But the Vickers hardness and fracture toughness first decrease and then increase with the increase of whisker content,which is consistent with the change trend of relative density.indicating that a small amount of Si C crystals is added to the ZTA matrix.It shows that adding a small amount of Si C whiskers in the ZTA matrix can strengthen the composites.The thermal diffusivity of ZTA-Si C_w composites improved with the increase of whisker content.With the increase of sintering temperature,the mechanical properties of ZTA-Si C_w composites with 10.0vol%whiskers basically maintained in the selected temperature range;while their thermal diffusivity and thermal conductivity continued to increase.The main toughening mechanisms of composites are transgranular fracture toughening,crack deflection,branching and bridging toughening,phase transformation toughening of zirconia,and whisker drawing and fracture toughening.The fracture mechanism of the composites is the mixed mechanism of transgranular and intergranular fractures.2.The Al₂O₃-Si C_w composites:The small amount of Zr O₂ phase was introduced during the preparation of composite ceramics.With the increase of Si C whisker content,the grain size of the composite ceramics decreased significantly,and the Vickers hardness and fracture toughness increased significantly.It indicates that the addition of Si C whiskers into the Al₂O₃ matrix can harden and toughen the composites.The thermal diffusivity and thermal conductivity of the composites decreased with increasing whiskers content.With the increase of sintering temperature,the grain size,fracture toughness,thermal diffusivity and thermal conductivity of Al₂O₃-Si C_w composites with whisker content of 10.0 vol%increased continuously in the selected sintering temperature range.While the relative density and Vickers hardness first increases and then decreases.3.He ion irradiation of Al₂O₃-Si C_w composites:Irradiation did not change the phase composition of the composites,but slightly degraded the crystallinity and phase structure of the composites.There are lots of helium bubbles in the multiphase ceramics,where mainly distributed in the?-Al₂O₃ grains,various grain boundaries and phase boundaries.There are no obvious helium bubbles in the t-Zr O₂ grains.The Nano-hardness and Young's modulus of the composite ceramics were slightly hardened after irradiation at room temperature,indicating that the Al₂O₃-Si C_w composites have good radiation hardening resistance.The size of the helium bubbles increased after high temperature irradiation,and the formation of microcracks was observed in the peak region,which reduces the degree of irradiation hardening of composites.4.Si ion irradiation of ZTA-Si C_w composites:After irradiation,the t-Zr O₂ phase in the composites undergoes lattice swelling,and the crystallinity and phase structure of?-Al₂O₃ and Si C phases degenerate.With irradiated at room temperature,at the irradiation dose reached 1.80×10¹⁷ ion/cm~2,an amorphous band was formed in the irradiation peak area,and its width in different grains was different.The hardness and modulus of the composite ceramics decreased significantly,which indicates that the irradiation causes the material to soften.When the irradiation temperature increased,the irradiation damage was recovered to extent,and the softening phenomenon was basically recovered,which indicates that the ZTA-Si C_w composites had good high-temperature radiation resistance.