Study On Process And Mechanism Of Bonding Irradiated Resistance SiC Ceramic Using YAS Glass-Ceramic

Nuclear power is a clean,reliabile and economical new green energy.With the gradual consumption of fossil energy,nuclear power plays an increasingly important role in power supply.The development of nuclear power is based on the safety of nuclear energy.Nuclear fuel cladding is a key component to ensure no leakage of nuclear fuel.Silicon carbide?SiC?ceramics has great potential in the application of nuclear reactor structural materials in the future,due to their high strength,excellent resistance of oxidation,stability of high temperature and low neutron absorption cross-section.Because of the inherent brittleness of SiC,it is difficult to produce large and complex shape components by machining operation methods.So they need to adopt appropriate joining technology to ensure the airtightness of the joint.Based on this background,the paper adopted YAS based glass-ceramic solder with good irradiation resistance to realize the joining of SiC ceramics.Combined with the phase diagram,the solder with a mass ratio of 36Y₂O₃-21Al₂O₃-43 SiO₂ was designed by simulating the radiation damage of the possible products generated in the SiC ceramic joint bonded by YAS glass solder.The effect of joining parameters on joints microstructure and mechanical strength was systematically studied,and the formation mechanism of joints was also explained.Through analysis of Y₂O₃-Al₂O₃-SiO₂ ternary phase diagrams,the possible phases in the SiC/SiC joints bonded by the YAS solder was Y2Si2O7?Al6Si2O13 and SiO₂,the simulation results indicated that the peak value of irradiation damang and He concentration of the glassy phases in the joints were significantly different from that of SiC ceramic,and the crystallization of glass can make the irradiation damage and He concentration distribution of the weld closer to SiC parent material.The designed glass solder melts completely at around 1400 oC and can transform into glass-ceramic by precipitation of yttrium silicate crystals.Glass-ceramic and SiC have good thermal matching,and the difference of thermal expansion coefficient between them was only 13.3%.The glass-ceramic was irradiated at 400 oC with 320 ke V He+ to 3×1016ions/cm2? 1×1017ions/cm2? 3×1017ions/cm2,respectively.There was no serious amorphous phenmennon generating in the glass-ceramic of the joints,and the type of crystal phase did not change.Joining of SiC ceramic was by two different kind of methods,one was direct joining method,the other was two-step joining method.The results showed that the wetting angle of YAS Glass solder on SiC ceramic surface is 40o,and the precipitated crystalline phases in joints fabricated by direct joining method were Y2Si2O7 ?Al6Si2O13 and SiO₂.The typical structure of joint can be expressed as: SiC ceramics/Y2Si2O7+ Al6Si2O13 + SiO₂+Glass/SiC ceramics.With the joining temperature elevating,silicon dioxide was only persisted in a stable coesite form and the crystalline products gradually tended to be amorphous.Through optimization of joining process parameters,the shera strength of joints reached to 46 MPa when joining parameter were 1420 oC/10 min.In order to enhance the bonding strength of the interface in the joint,a two-step joining method was proposed for joining SiC ceramic on the basis of direct joining method.The silica film was formed on the surface of SiC through a pre-oxidation treatment,which incent to the wetting angle of YAS solder to the SiC ceramic drop from 40o to 20o.Two-step joining method improved the interface combination between joining seam and SiC base,and the shear strength of joints reachend to 48 Mpa at 1420 oC for 10 min.The crack propagated along on the side of SiC ceramic.