Brazing Process And Joining Mechanism Of SiC Ceramic Joint Brazed With Silicon-based Composite Filler

Silicon carbide（SiC）ceramic has excellent mechanical properties at room temperature,such as high bending strength,excellent oxidation resistance,good corrosion resistance,high abrasion resistance and low friction coefficient.Also,the high temperature mechanical properties（strength,creep resistance,etc.）are the best among known ceramic materials and has very low radioactivity.SiC ceramic can be used in key components such as turbine blades of aviation engines and cladding structural materials of nuclear fusion reactors.It is considered to be an ideal structural material in relatively harsh environments,and has wide industrial application prospects.However,due to the very high hardness and brittleness of ceramics,the requirements on equipment and preparation process are relatively high,which also increases the processing difficulty of ceramics.Therefore,the joining is the best way to obtain large-sized and complex-shaped components.Brazing is widely used because of its convenience,low cost and high quality.In this paper,high temperature brazing filler metals Si and Si-Al eutectic alloy are used to braze SiC ceramics.At the same time,adding the second phase can reduce the thermal expansion coefficient of the joint and improve the microstructure of the joint.Thus,phenolic resin（PF）and TiC particles are added to Si,B₄C and Ti particles are added to Si-50Al eutectic alloy to form composite brazing filler metals to braze.It is feasible to braze SiC by Si and PF brazing filler metals,and the joint is well-brazed.Adding PF can effectively improve the microstructure of the brazing seam.With the increase mass fraction of PF,the volume fraction of SiC ceramic phase increased gradually.However,when excessive PF was added,holes will appear in the joint.When 6 wt.%PF is added,the shear strength of the joint reaches a maximum of97.84 MPa,which is 80.8%higher than that of the joint with Si.The joint was basically broken at the joint interface between SiC ceramic and brazing filler.It is feasible to braze SiC by Si and TiC brazing filler metals,and the joint is well-brazed.In the brazing process,Si reacted with TiC and formed SiC and Ti₃SiC₂ceramic phases.With the increase mass fraction of TiC,the volume fraction of SiC and Ti₃SiC₂phases increased gradually.When 7 wt.%TiC was added,holes appeared in the brazing seam.When 3 wt.%TiC is added,the shear strength of the joint reaches the maximum value of 101.98 MPa,which is 88.5%higher than that of the joint with Si.The joints brazed with TiC and Si were mainly broken at the brazing filler metal.It is feasible to braze SiC by Si-50Al,B₄C and Ti brazing filler metals,and the joint is well-brazed.Si-Al reacted with B₄C and Ti formed SiC and Ti B₂ceramic phases.With the increase mass fraction of filler metals,the volume fraction of SiC and Ti B₂phases increased gradually.When 3 wt.%B₄C and Ti are added,the shear strength of the joint reaches the maximum value of 114.32 MPa,which is 61.8%higher than that of Si-50Al joint.The joints brazed with B₄C and Ti particles addition were mainly broken at the brazing filler metal.