Titanium and titanium alloy are good materials for diffusion welding, because its surface oxide film is easy to dissolve at diffusion temperature. When liquid diffusion bonding is applied, a layer of other metals must be placed on the interface between the titanium surface. Generally, the metal can form a eutectic with low melting point with titanium. During the brazing heating stage, the liquid metal flow is irregular to the matching place. At a later stage, the liquid layer diffuses into the matrix metal, making the weld completely solidified before the end of the heat cycle.
In recent years, the application of diffusion welding as a method to connect titanium and its alloys has attracted people's interest. Solid state welding has the following limitations: the surface must be the actual optical plane; in order not to affect the performance of the alloy, the diffusion must be carried out at a low enough temperature, so the diffusion is very slow. Liquid diffusion welding can reduce the precision of matching by forming unstable liquid film on the interface, and also accelerates the diffusion process.
Because higher interfacial pressure and plastic deformation at high temperature are conducive to solid state connection, it can sometimes connect the sequence with the hot working procedure that reduces the cross-sectional area of the material. Rolling diffusion bonding is an example. In this process, titanium alloy parts are fixed in a titanium shell, and the titanium shell is evacuated and sealed to die. The characteristics of such welded joints are good strength, plasticity and corrosion resistance, but the difficulty is that the surface quality and technological parameters are difficult to control, which may affect the dimensional accuracy of products. Another difficulty is that the solid-state static diffusion connection must be carried out in argon or vacuum.
(1) the contact spot welding, seam welding, argon arc welding, plasma welding and electron beam welding technology can be used for welding of titanium.
(2) it is generally believed that commercially pure titanium and some low strength titanium alloys are weldable, but the welding performance of titanium alloys with higher strength is not satisfactory due to the decrease of plasticity after welding.
(3) titanium can not be welded to other metals by general fusion welding, because this will form a metal compound to form a very brittle weld.