Microstructure And Mechanical Properties Of TiAl Alloy Brazed Joints Using Amorphous Alloy Filler

TiAl alloy has the advantages of low density,high modulus of elasticity,good strength,excellent oxidation resistance and creep resistance.Thus,TiAl alloy can perform excellent characters in aerospace and military industries based on the advantages mentioned above.The excellent properties of ZrB2-SiC composite ceramics at high temperatures can ensure reliability during service life.Therefore,the realization of the self-joining of TiAl alloy and the connection with ZrB2-SiC ceramics is of great significance to aerospace.In this paper,the TiAl alloy(Ti-48Al-2Cr-2Nb)itself was vacuum brazed under different processes conditions by using CuTiZrNi amorphous alloy filler.The connection was successfully realized in each process.The typical joint interface structure is:TiAl/Ti2Al/AlCuTi/(Ti,Zr)2(Cu,Ni)+a-Ti/TiAl.As the brazing temperature increases or the holding time increases,the width of the interface reaction layer increases,the width of the central reaction zone decreases.The a-Ti can be increased by increasing the brazing temperature and the a-Ti in the central reaction zone can be decreased by prolonging the holding time.The shear test shows that as the brazing temperature increased or the holding time prolonged,the joint shear strength first increased and then decreased.when the brazing temperature is 940 ? with the holding time of 20 min,the joint shear strength reached a maximum of 311 MPa.During the shearing process,the crack initiates in the brittle(Ti,Zr)2(Cu,Ni)phase.With the action of external stress,the crack extends to the interface reaction layer,and the fracture contains a large number of cleavage planes.There are more cleavage steps and the fracture mode of the joint is cleavage fracture.After the successful achievement of the TiAl alloy self-joining,the TiAl/ZrB2-SiC ceramics were continuously vacuum brazed by CuTiZrNi amorphous alloy filler.When the brazing temperature of 970 ? and the holding time of 10 min,the joints produced cracks due to excessive residual stress.The joints were well bonded under other processes conditions,and no defects such as holes and cracks were founded.The typical joint interface structure is:TiAl/Ti2Al/AlCuTi/(Ti,Zr)2(Cu,Ni)+TiB+TiB2+TiCu/Ti5Si3+TiC/ZrB2-Si C?The micro structure of the joint is greatly affected by the process.When the brazing temperature is low or when the holding time is short,the size of each precipitate phase in the joint is small.With the brazing temperature increasing or holding time prolonging,both the content of the precipitated phase and the size increase,but a new precipitate phase is not formed.The shear test shows that as the brazing temperature increased or the holding time prolonged,the joint shear strength first increased and then decreased.when the brazing temperature is 910 ? and the hoiding time is 20 min,the joint shear strength reached a maximum of 187 MPa.After analyzing the fractures of each process,it is found that the joints are all broken on the ceramic side,the crack initiates from the brazing seam and extend to the ceramic side while and the fracture mode is brittle fracture.