Vacuum Brazing Of Dissimilar Metals Between Titanium Alloy And Steel

Titanium and its alloys possess many excellent properties such as high specific strength and good oxidation resistance, making them widely used in modern industry especially in aerospace and chemical industry. However, the extensive applications of titanium and its alloys are restricted by their high cost and complex manufacturing process. Joining titanium and its alloys to other materials such as structural steel or stainless steel is an important approach to reduce cost and a necessary way to manufacture complicated components. However, there are many difficulties when jointing titanium and its alloys to steel. In this paper, y-TiAl alloy/40Cr steel and TC4titanium alloys/304stainless steel dissimilar metals combinations were vacuum brazed using new Ti-Cu based amorphous alloy foils. The microstructure, element distribution and phase composition, mechanical properties and fracture analysis of the brazed joints were investigated.Sound joints without pore and crack were obtained when vacuum brazing y-TiA1alloy to40Cr steel with Ti-Cu-Ni-Zr-Sn, Ti-Cu-Ni-Zr, Cu-Ti-Ni-Zr-V amorphous alloy foils and pure Cu foils and vacuum brazing TC4to304stainless steel with Cu-Ti-Ni-Zr-V amorphous alloy foils.The brazed seam of y-TiAl/40Cr joint with Ti-Cu-Ni-Zr-Sn amorphous alloy foil can be divided into two regions:a layer mixed Ti(Ni, Cu)Al with Ti-A1compounds, filler metal and Ti-Sn and Ti(Cu, Ni) compounds mixture distrtbuted in the filler metal region. In the joint brazed with pure Cu, the diffusion of Ti can’t be restrainted by the Cu foil, and Ti-Fe intermetallic compound would be produced because of the enrichment of Ti in the steel side.The highest shear strength of the y-TiA1/40Cr joint brazed with Ti60Cu10Ni22Zrs (at.%) was32MPa. Three kinds of joints with different holding time all fractured through the interface between40Cr base metal and filler metal where more Ti and A1were detected. The formation of Ti-Al intermetallic was thought to make this region the weakest part of the joint.The y-TiA1/40Cr joint brazed with Cu37.5Ti25Ni12.5Zr12.5V12.5(at.%) possessed a shear shength of136MPa. Fracture of the joint happened through the gray lay, consisting of intermetallic phases, because of the enhancement of the bonding strength between40Cr and filler metal by the irregular protuberant Ti-based solid solution. The shear strength of the y-TiAl/40Cr joint brazed with Cu43.75Ti37.5Ni6.25Zr6.25V6.25(at.%) was38MPa. Fracture of the joint happened through the diffusion layer, due to the production of Ti19A16and Ti2Cu in the flat diffusion layer. These results prove the appropriateness of designing amorphous alloy with less Ti and more V for brazing y-TiAl alloy to steelBy comparing the brazing results of TC4/304ss with y-TiA1/40Cr, it can be found that Cu-Ti-Ni-Zr-V amorphous alloy and304stainless steel showed better compatibility than Cu-Ti-Ni-Zr-V amorphous alloy and40Cr steel. The shear strength of the TC4/304ss joint brazed with Cu43.75Ti37.5Ni6.25Zr6.25V6.25(at.%) was105MPa, and the shear strength of the TC4/304ss joint brazed with Cu37.5Ti25Nii2.5Zri2.5Vi2.5(at.%) was116MPa. All the joints fractured through the gray phase in the filler metal layer. The generation of Cr-Ti, Fe-Ti, Cu-Fe-Ti and Fe-Ti-Zr intermetallic compounds resulted in the initial fracture of the joint.