Diffusion Bonding and Electron Beam Diffusion Bonding of Titanium and Titanium Alloys

Advantages of Diffusion Bonding

· Limited microstructural changes

· Can join dissimilar titanium alloys

· No filler required

· Can fabricate very complex shapes, especially using superplastic forming

Disadvantages of Diffusion Bonding

· Slow

· High vacuum required

· Expansive equipment

Conventional Diffusion Bonding

Titanium is the easiest of al common engineering materials to join by diffusion bonding, due to its ability to dissolve its own oxide at bonding temperatures. Conventional diffusion boding is a slow process and requires careful control of temperature, and joint face alignment. The process also needs to be undertaken in a vacuum. Under ideal conditions a bond of very high quality can be made with no flash formation. However, the process is slow, and requires considerable precision, making it unattractive for field use, although it has been used in the aerospace industry, in particular with superplastic forming. The process, including superplastic forming, is also used in the successful development of titanium compact heat exchangers.

Electron Beam Diffusion Bonding

This process is a variant of diffusion bonding in which only the interface region is heated, resulting in a considerable energy saving. The heating source is an electron beam which is swept over the area of the joint at such a speed that fusion of the titanium alloy is prevented. A force is applied across the joint. As the heated area is very limited, higher forces can be used can be used without the risk of plastic collapse of the components being welded, resulting in a significant reduction of welding time, typically by an order of magnitude. The process has been investigated for joining several titanium aluminide alloys to themselves and other titanium alloys, and for joining titanium alloys. Very good results have been reported from these trials, but to date the process has not been used commercially.