Exposing the secrets of brazing titanium, a common activity for a not so common metal
Brazing titanium related issues appeared as the complexity level of applications of the glamour metal gradually increased over its initial development stage.
What is brazing anyway? Well, brazing is a metal-working procedure that is used for joining two materials together with the use of a third component. As opposed to
, brazing process does not imply the melting of the components that are to be joined. Brazing is often mistaken to soldering, as soldering is also based on the same primary concept, but in brazing the filler metal has a melting point greater than 800°F (430°C), but less than that of the materials to be joined.
Brazing titanium is usually accomplished in a closed furnace and implies some specific precautions, due to the properties of the metal. In the first instance, titanium is known to become embrittled by the absorption of hydrogen, nitrogen an oxygen gases. That’s why titanium brazing is done in a vacuum or in an inert gaseous atmosphere. Further verification of the existence of contaminants from previous brazing operations is also recommended.
The choice of the filler metal is again a critical decision. Nickel and materials containing nickel in large quantities are generally avoided as nickel and titanium tend to alloy at a low temperature. The most common filler materials used in brazing titanium is silver, alloyed by lithium, copper, aluminum or tin. The use of silver has been lately reduced to some limitations of a certain range of products, coming mostly from military products, and the replacement was class of special
, containing cooper, zirconium or beryllium that were more adequate to the increasing industry requirements.
In addition of furnace brazing a laser titanium brazing process was developed to use in those parts that are not suitable for furnace processing, such as titanium sheets. The laser brazing technology, by selectively heating brazing spots, substantially reduces the heat impact, reducing the potential changes of titanium structure due to thermal exposure. The process must be thoroughly controlled though as there is a higher risk of material oxidation.
Normally, the brazing or soldering of titanium to itself, or to other materials is not possible within domestic or small industry possibilities. Theoretically, a hand torch a sufficient low melting point filler metal could be used to make low strength joints, but practical results are heavily influenced by operator’s skill and with common error leading to complete failure, it’s not feasible. And what would be the point of choosing titanium for its strength and needing a low yield bond to make ends meet?
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