Investigation On Brazing Process And Connection Mwchanism Of SiC Ceramic Matrix Composites With Invar Allor

SiC ceramics have excellent mechanical properties, good thermal conductivity, low coefficient of linear expansion and good thermal stability, wear resistance, corrosion resistance and creep resistance, it is an ideal high-temperature corrosion-resistant material, and therefore it was elected to do alternative materials ethylene cracking furnace interior cavity pyrolysis tube cracking tube improved high temperature capability to improve lysis efficiency and yield of ethylene cracking furnace. In practice, SiC ceramics and metals require connection, Invar alloy is a typical low expansion alloys, easier to implement effective ceramic-metal connection, so often used to connect with the ceramic. Firstly, by NiCrSiTi solder for SiC ceramic and Invar alloy connection through experiments to explore the cooling rate, the brazing temperature, holding time and other process parameters on the brazed joint microstructure and properties of the obtained brazing SiC ceramic and Invar alloy most good process parameters. Based NiCrSiTi solder connection mechanism of the base material, to design composite solder joints relieve residual stress and improve the mechanical properties of the joint, and ultimately SiC ceramic and Invar alloy valid connection.When using NiCrSi-0Ti brazing filler SiC ceramic and Invar alloy solder joint experiments, typical joint structure of the brazing material is SiC ceramic / Ni + Fe3 Si + CrSi2 / CrSi2 + [Fe, Ni] + Ni3Si2 + Ni3 Fe / Cr3Ni5Si2 + Fe2 Si + FeNi / Invar alloy. Brazing process parameters have a major impact on the organization and performance of the brazing material is found through experiments. First, the cooling rate is faster when the joint is large residual residual stress, poor joint performance, when the cooling rate is slow, the joint performance is improved; secondly with the brazing temperature increases so brazed joint organization changed significantly, the joint organization first loose change by the dense, then due to higher temperature lead to thickening of the ceramic side of the reaction zone, the residual stress increases, reduced performance; similar joint organization and holding time on the properties of the brazing temperature, with the holding time, the joint shear after the first increase shear strength decrease. Clearance Experimental Inquiry found that when using NiCrSi-0Ti solder brazing experiments, the optimum parameters are: brazing temperature 1180 ℃, holding time of 15 min, the joint shear properties obtained at this time is 36 MPa.Based on the previous experiments to further explore the impact of Ti content on the microstructure and property, and found that when the brazing filler added Ti, soldered joints of the first increase after a decrease, when brazing alloy Ti content of 5wt%, the maximum strength of the joint the value of 46.7MPa, ceramic side after Ti added 2Fe+Ti = Fe2 Ti, avoiding brittle phase Fe2 Si presence slows the stress probability of microcracks ceramic layer and measured response by analysis.To weld the resulting product(Fe3Si, CrSi2, Fe2 Ti, [Fe, Ni], Ni3Si2 etc.) thermodynamics and kinetics analysis, found that these products can be formed. In the experiment proved the existence of these substances by XRD, EDS, SEM and other testing methods. Mechanism NiCrSiTi solder connection SiC ceramic and Invar alloy adopted as: With the brazing temperature, the solder melts gradually, beginning in the molten solder contacts SiC ceramics react brazing alloy elements Ni and ceramics the Si produced by the reaction Ni3 Si, while the side of the molten metal into the Invar alloy solder and brazing filler metal elements produced by the reaction Fe2 Si phase, FeNi phase, intermediate reaction zone contains a variety of elements to undergo complex reactions generated [Ni, Si ], [Fe, Ni], and other compounds, and ultimately the connection joint.To further improve the performance of the connector, designed composite solder containing SiC particles NiCrSiTi(SiC), through experiments found that the addition of SiC particles composite solder can reduce the thickness of the ceramic side of the reaction layer, slowing the residual stress at the joint, improve solder shear strength of welded components. Experimental analysis found brazing alloy SiC priority in response to alleviate the erosion of SiC ceramics, ceramic-side reaction layer thinner, relieve residual stress joints, improve joint performance by.