Study On The Solid Phase Reaction Of SiC Ceramic/transition Metal(Ta,Cr,Nb,Zr) Interface

Owing to the high melting-point,high strength,hardness,excellent wear resistance,good corrosion resistance and low neutron cross-section,silicon carbide?Si C?are used as the components in the fields of engine,nuclear and bulletproof armors.The brittleness of Si C ceramics makes the machining difficult.By means of the joining process or formation of the composite,Si C component with the complex shape can be prepared.Whereas,the possible reactions between Si C and metal would affect the properties of the materials,providing the servicing environment or the processing conditions under high-temperature/pressure.By combining the microstructural analysis,thermodynamic analysis and the literature comparison,this study focused on the solid state reaction and diffusion mechanisms between Si C ceramics and transition metal elements?Me;Me=Ta,Cr,Nb and Zr?by using the brazing furnace and spark plasma sintering?SPS?.Ultra-high vacuum(10^-5Pa)and high processing temperature?1400?1800??were given by the brazing furnace;while,the external pressure?30MPa?,moderate temperature?1200?1400??and carbon-rich environment were provided by SPS.The main research content and conclusion are as below:The interfacial microstructure,elemental distribution and the diffusion depth of diffusion couple of Si C-Me under high temperature?1400?1800??and vacuum(10^-5Pa).It was found that only reaction region occurred on the surface of metal for the diffusion couples of Si C-Ta,Si C-Nb and Si C-Zr without any evidence of joining.On the other hand,as for the diffusion couple of Si C-Cr,the mutual diffusion and joining were observed.When lifting the temperature from 1400?to 1800?,the thickness of the reaction region on the surface of Me increased from 5.6?m and 8.1?m to 22.2?m and 41.0?m for Si C-Ta and Si C-Nb,respectively.Meanwhile,the thickness of Si C-Zr increased remarkably from 6.4?m at 1400?to 640.7?m at 1600?,where the layer separation was observable.As for Si C-Cr,the elements of Si and C diffused through Cr after processing at 1600?.The interfacial microstructure,elemental distribution,the diffusion thickness of Si C-Me under the temperatures of 1200-1400?and the uniaxial pressure of 30MPa were investigated using SPS furnace,which was feature with rich carbon/graphite environment.It was reveal that the reaction region was evidenced in the surface of metal side for all four diffusion couples of Si C-Me?Me=Ta?Nb?Zr?,of which Si C-Ta,Si C-Cr enabled the joining.The reaction region was relatively limited for Si C-Ta and Si C-Nb,when elevating the temperature from 1200?to 1400??7.0?m for Si C-Nb after heating at 1400??.Simultaneously,the thickness of the reaction region?on Me side?increased significantly for Si C-Cr and Si C-Zr,particularly Si C-Cr,as the temperature increasing.For Si C-Zr,it increased from 6.4?m to 70.0?m when temperature increased from 1300?to 1400?.For comparison,the elements of Si and C diffused through Cr part at 1300?,which promoted the reactions between Cr and graphite resulting from the co-effects of temperature and pressure.By combining the microstructural and elemental analysis,and literature report,the diffusion product of Si C-Me was analyzed and the difference of solid-state reaction between brazing furnace and SPS furnace was compared.Ta C and Ta Si₂was detected as the product on Ta surface for Si C-Ta.The initial product was Cr₅Si₃and Cr₂₃C₆for Si C-Cr,while,the diffusion path of Cr₅Si₃C_x/Cr₇C₃/Cr₅Si₃C_xwas observed as the reaction/diffusion completed.The diffusion path was found to be Nb Si₂/Nb₅Si₃C_xfor silicon and Nb C/Nb₂C for carbon,respectively.In contrast,the diffusion path of silicon and carbon from Si C towards Zr was Zr Si₂/Zr Si/Zr₅Si₃C_x/Zr₂Si and Zr C₄/Zr₅Si₃C_x/Zr C.When diffusion performed in the brazing furnace,the thickness of the reaction region of Si C-Ta and Si C-Nb increased slowly as the temperature elevating from 1400?to 1800?,indicative of the good thermal stability at high temperature.Nevertheless,the thickness of Si C-Cr and Si C-Zr increased significantly,which indicated the high reactivity.Due to the good stability at high temperature for Si C-Ta and Si C-Nb,no variation of the reaction region?in terms of the thickness?was observed after heat-treatment at the moderate temperature range?1200?1400??in SPS furnace,where the external pressure was applied.Because of the high reactivity of Cr and Zr with Si C,the thickness on the metal surface increased remarkably and quickly with the presence of the pressure even at relatively low temperature of 1200?1400?.