Microstructure,mechanical Property And Joining Of Ti₃SiC₂ Based Composite Ceramics

Ti₃SiC₂ ceramic possesses a broad application prospects in self-lubricating materials,nuclear reactors and other fields due to their dual properties of metal and ceramics.As a structural and functional material,the hardness and mechanical properties of Ti₃SiC₂ ceramics need to be further improved.In addition,it is necessary to realize the preparation of complex shape parts through material connection in practical applications.Hence,it is of great value and significance to improve the comprehensive mechanical properties of Ti₃SiC₂ ceramics and develop reliable ceramic bonding technology.In this paper,Ti₃SiC₂-SiC-Ti B₂-Ti C composite ceramics were fabricated by in-situ reactions of B₄C and Si with Ti₃SiC₂.The second-phase Ti B₂,Ti C and SiC with high hardness and strength were introduced to refine the microstructure of the matrix.The effect of second-phase addition on the phase evolution,microstructure and mechanical properties of the composite ceramics were analyzed,the synergistic strengthening of Ti₃SiC₂ ceramics was realized.Ti₃SiC₂ based composite ceramics were brazed with Ag-Cu-Ti solder.Ag-Cu-Ti-x LAS composite filler metal was prepared by addingβ-eucryptite powder（LAS）with negative expansion coefficient to Ag-Cu-Ti filler metal.Ti₃SiC₂ based composite ceramics were joined by brazing technology with Ag-Cu-Ti-x LAS composite filler.The microstructure and mechanical properties of the joint were characterized and analyzed.High density Ti₃SiC₂ based composite ceramics were prepared via spark plasma sintering（SPS）at 1380℃and 50 MPa using Ti₃SiC₂,B₄C and Si as raw materials.Marvellous mechanical properties were obtained for the Ti₃SiC₂-10 wt.%B₄C-5wt.%Si composite ceramics,including the relative density and porosity were 99.3%and 0.12%respectively,the Vickers hardness was 13.5 GPa,the flexural strength at room temperature was 483.5 MPa,and the fracture toughness was 7.2 MPa·M^1/2.Compared with Ti₃SiC₂ ceramics,the hardness and flexural strength of Ti₃SiC₂ based composite ceramics were increased by 187.2%and 16.9%,respectively.In addition,the mechanical properties of Ti₃SiC₂ based composite ceramics are excellent at high temperature,the three-point bending strength of the composite ceramics at 600℃and800℃was 497.5 MPa and 488.1 MPa,respectively.Under the brazing temperature of 830～890℃,the reliable brazing connection of Ti₃SiC₂ composite ceramics were realized by using Ag-Cu-Ti solder.The interface reaction layer was mainly composed of Ti₅Si₃ and Ti C,which were formed by the reaction of Ti and SiC.The nano Ti C particles would diffuse into the liquid solder and acted as the nucleation particle to refine the microstructure of the solder.With the increase of brazing temperature,the reaction between Ti and SiC was more sufficient,and the serious aggregation of Ti C particles and other phases appeared in the intermediate layer of the solder,which made the microstructure of the joint connection layer unevenly distributed.The room temperature shear strength of the joint reached the maximum value of 81 MPa at 870℃.Under the brazing temperature of 870℃and holding time of 10 min,the wetting angle of Ag-Cu-Ti-x LAS on Ti₃SiC₂ composite ceramic increased with the increasing of LAS;Outstanding joint shear strength was obtained when the joint was used the Ag-Cu-Ti-3 wt.%LAS,reached 97 MPa,which was 20%higher than that of the brazed joint without LAS particles.The results shown that the addition of LAS reduced the thermal property difference between Ag-Cu-Ti-x LAS composite solder and Ti₃SiC₂ composite ceramic,and the residual stress of brazed joint was relieved.