Formation mechanism of titanium/steel brazing joints with thermally sprayed Ni layer

In the brazing joint of titanium alloy to stainless steel, a lot of Fe-Ti intermetallic compound can be easily formed to make joints cracking. To solve this problem, a procedure was developed that Ni coating was deposited as the lap joint face of titanium/steel in resistance brazing process. Meanwhile, the mechanical properties, the microstructure and the composition of the brazed joint with thermally sprayed layer with different thickness was studied. The formation mechanism of brazing joint with preplaced Ni layer was discussed. Experimental results showed, when a reasonable thickness of Ni layer acted as a part of the brazing joint, the concentration of diffused Fe, Cr, Ti and other atoms declineed due to the presence of Ni layer. Moreover, Ni atoms can combined with Fe, Cr, Ti and other atoms, making the number brittle Fe-Ti, Cr-Ti intermetallic compounds decreased obviously, therefore it improved the mechanical properties of the joint significantly. Under the combined effect of the coating and solder, a kind of microstructure induced by multiple reactions was formed, which played a transitional role in the joint, it is also the main reason for the mechanical properties improvement of joints.