Microstructure And Mechanical Properties And Brazing Process Of TiBw/TC4Composite Joint

Due to the low density, excellent resistance to corrosion, abrasion and hightemperature, TiBw/TC4composite has been widely attracted and expected forapplications. It is critically important to investigate the bonding of TiBw/TC4inboth theory and practice. In this work, Ti-Zr-Cu-Ni alloy and Ti-Zr-Cu-Ni alloyincorporated with TiB₂particles composite filler were used to join the TiBw/TC4composite to itself to meet the different environmental applications. The effects ofbrazing parameters and the composition of the filler on the microstructure andmechanical properties of joints were investigated and the formation mechanism ofthe joint was analyzed.TiBw/TC4-TiBw/TC4joints brazed with Ti-Zr-Cu-Ni consist of titanium-based solid solution which contains small lamellar phase[（Ti,Zr）₂Cu（Ni）+Ti（S.S）],（α+β） Widmanstatten microstructure and TiBw/TC4matrix when bonded at1193Kfor10min. Bonding strength of joints depends on the morphology of both whitelamellar phase located in the centre of seam and Widmanstatten microstructure atthe edge of joint, which is influenced by the filler thickness, brazing temperatureand holding time. The seam could not be filled completely due to lacking of thefiller. On the contrast, amounts of intermetallic compounds formed and aggregatedin the seam, which deteriorated the bonding strength. The optimal thickness of filleris30μm in present experiment. The shear strength increased sharply with brazingtemperature increasing to1200K and tended to be stable up to1260K, which isaround520MPa, and then decreased with temperature further increasing. Theinfluence of holding time on the strength relies on temperatures. Under1223K, theshear strength increases with prolonging time to30min, and comes to be stable.The shear strength reached the maximum value when bonded at1253K for10min.The tensile strength of1067MPa can be reached when bonded at1223K for30min,and the joint failured in the matrix.The TiBw/TC4-TiBw/TC4joints brazed with Ti-Zr-Cu-Ni+10vol.%TiB₂consist of （TiBw+（Ti,Zr）₂Cu（Ni））/α-Ti composite located in the centre of joint,（α+β） Widmanstatten microstructure close to matrix and matrix. TiBw was formedin situ first and distributed uniformly in the joint when bonded at1253K for10min.The dimension of the TiBw varies from several micron to dozens of micron, andsome of them grow into the matrix. The microstructure of the brazing seam becamemore uniform and fine owing to the in-situ formation of TiBw. Meanwhile, theintermetallic compounds distributed uniformly in the joint and the content decreased correspondingly. Bonding strength is lower compared with joints brazed with thesingle Ti-Zr-Cu-Ni filler, because the plastic deformation of the brazing alloybecame weaker and more defects appeared in the joints gradually, but the shearelasticity is higher. Elevating temperature or prolonging time，the seam mainlyconsist of TiBw, which containes many defects and resulting in the lower bondingstrength. The shear strength of481MPa in room temperature was reached usingfiller with10vol.%TiB₂at1253K for10min. When tested at773K or873K, boththe bonding strength and shear elasticity are superior to that brazed with the singlefiller, and the shear strength is over400MPa. When tested at higher temperature, itpresented more obvious advantages using composite filler.