| Silicon carbide(SiC)ceramic has great potential used in nuclear field because it possesses high strength,excellent oxidation resistance,good high temperature stability,good corrosion resistance and low thermal neutron absorption cross-section.It's one of the possible core structure materials for 4th generation reactor.By achieving the joining of SiC ceramic and zirconium alloy,on the one hand,the brittleness and poor machinability of ceramic materials can be overcome,and the application of SiC in reactor will also be promoted.On the other hand,the safety and efficiency of power plants can be enhanced without changing the current design specifications.Beased on this background,brazing was choosen as the join method to join SiC ceramic and Zr4 alloy,through the simulation of irradiation damage of possible phases in the joints brazed by TiZrNiCu filler,and combined with phase diagram analysis and caculation of Zr activity in Zr-Ni system,the Zr-24Ni(at.%)eutectic filler was designed.Then the Zr-24 Ni and TiZrNiCu filler were used to join SiC ceramic and Zr4 alloy,effect of brazing parameters on joints microstructure and mechanical properties was studied,and the formation mechanism of the joints was also explained.What's more,He+ irradiation experiment was performed,microstructure changes on SiC/brazing seam interface area and swelling coordination between different phases were analyzed.Through analysis of Zr-Ti-Ni and Zr-Ti-Cu ternary phase diagrams,the posible phases in the SiC-Zr4 joints brazed by TiZrNiCu filler was Zr2Ni,Ti2Ni,ZrNi,TiNi,ZrTiNi,Zr2Cu,Ti2Cu,ZrCu,TiCu,Cu2 ZrTi,the simulation results indicated that ZrNi compounds might have better irradiation resistance.Combined with Zr-Ni binary phase diagram and caculation of Zr activity in Zr-Ni system,the Zr-24 Ni filler was designed as the new filler system.For Zr-24 Ni filler,the filler fabricated by ball milling method had poor flowability,and could not well spread out on the surface of both two substrates.The filler manufactured by arc-melting method showed excellent flowability on both materials,the wetting angle on SiC was about 4°,while that on Zr4 was 0°.SiC-Zr4 joints without any defects were obtained brazed by arc-melted filler,and the brazing seam mainly consisted of ZrC,Zr2Ni and Zr(s,s).In the process of joining SiC ceramic to Zr4 alloy using TiZrNiCu amorphous filler,it was found that Zr4 substrate dissolved into liquid filler in large quantities,of Zr-based solid solutuion and compounds.The typical structure of joints could be expressed as: SiC/(Zr,Ti)C/Zr2Si+(Zr,Ti)2(Cu,Ni)+(Zr,Ti)2(Ni,Cu)+Zr(s,s)+?-Ti/Zr4 alloy.Brazing parameter in the brazing SiC ceramic and Zr4 alloy using ZrNi filler was studied.The amount of Zr2Ni phase reduced with raising temperature and holding time as a result of increasing amount of overflowing liquid filler,while interfacial reaction was promoted and reaction layer became thicker.Through optimization of joining parameters,the highest shear strength of the joints reached 110 MPa when brazing parameter was 1060°C/15 min.The results of study on brazing parameters in the joining of SiC ceramic and Zr4 alloy indicated that with the increase of brazing temperature and holding time,new phases were not found in the joints,but the amount of overflowing filler increased,which decreased the amount of intermatellic compounds.The Size of Zr2 Si phase increased.The amount of dissolved Zr4 alloy increased with raising temperature,but didn't change with extended holding time.Shear strength of the joints first increased then decreased with increasing temperature and holding time.The highest shear strength of the joints reached 95 MPa at room temperature when the joints were brazed at 930 °C holding for 15 min.The two joints were irradiated by He+ ions at room temperature,and the interfacial structure on SiC side was observed using TEM.For the joints brazed by ZrNi filler,when the ion influnce was 1×1016 ions/cm2,phases in the interfacial area had no obvious changes;When the ion influence was improved to 5×1016 ions/cm2,an amorphous band was found in SiC substrate,and a damage peak area with dark contrast could be observed in ZrC reaction layer,while Zr2Ni was totally amorphization in the ion projected range.There was no uncoordinated deformation caused by the differences of irradiation swelling rate between different phases;When ion influence was improved to 1×1017 ions/cm2,high density He bubbles with nano sizes could be observed in these phases.The distribution of He bubble dengsity and sizes were different in different phases.For the joints brazed by TiZrNiCu filler,changes of SiC substrate and(Zr,Ti)C reaction layer after He irradiation with different ion influences were almost the same as SiC and ZrC in the joints brazed by TiZrNiCu filler,respectively.However,the amorphization region of(Zr,Ti)2(Cu,Ni)was broader than that of Zr2Ni,but the swelling rate of(Zr,Ti)2(Cu,Ni)is smaller than that of Zr2Ni.As a consequence,obvious hight difference between different phases were found in the joints brazed by TiZrNiCu filler,indicating a more coordinated deformation in interfaicial area of the joints brazed using ZrNi filler. |
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