Strongest brazing materials for titanium?

Question

What are the strongest brazing materials for titanium?

The main materials I would like to use would be copper or silver, in which case I would like to ask which would form a stronger bond with titanium. Otherwise what are the strongest bond forming materials for brazing nickel titanium wire to titanium?

Answer 1

To give at least some context to this. Titanium is generally considered 'exotic' for welding purposes as it is quite sensitive to both temperature change and contamination by atmospheric gasses, even at temperatures significantly below its melting point.

Like aluminium, titanium is quite reactive but protects itself from corrosion by formation of a stable oxide surface and any welding, brazing or soldering process will inevitably involve removing this layer.

Titanium can be TIG welded to itself without too much difficulty but this definitely comes under the category of 'advanced' welding in terms of both operator skill and equipment needed. In particular it needs good shielding on both sides of the weld. Indeed in some cases it may be preferable to weld it under an entirely inert atmosphere. The weldability also depends on the alloy with high alloy multi-phase alloys being more difficult.

Titanium can be brazed with the right filler and flux. Because of its reactivity vacuum brazing is an attractive option.

You might get away with using a low temperature silver solder with a fairly active flux but in general high strength brazed joints will need to be done under vacuum or an inert atmosphere.

Bear in mind though that titanium will burn in air if it gets hot enough.

Depending on your application you might want to to consider mechanical methods such as rivets or screws or look at adhesive joints.

Edit : brazing wires.

On one hand brazing can be a good way to attach wires to much larger metal parts because there is much less chance of melting the wire and it can form a neat and convenient joint. However it is less suitable for highly stressed applications for a couple of reasons.

• The brazing filler usually has a significantly lower strength than the base metal. This may not matter in certain types of joints (eg bicycle frames) where the joint is designed so that the contact area is much larger than the section of the members being joined but joining wire to a flat surface is not so good.
• Brazed joints are strongest when there is a relatively small and consistent gap between the surfaces being joined. This is hard to achieve with wire.
• Wire derives much of its strength from the drawing process (ie work hardening) so heating to brazing temperatures may well significantly reduce its strength.

Certainly brazing load bearing wires is not something that is seen very often. It is much more common to see some sort of mechanical (eg pressed, crimped or spliced) terminator....think bike brake cables and guitar strings. I'm not saying that it won't work but it doesn't sound like the best way to proceed to me.

One possibility would be to put an eye or ferrule on the end of the wire and TIG weld an attachment point to the joint, this is actually not that far off how biological tendon-bone attachments work.

In terms of steel vs titanium, you will certainly find steel a lot easier to work with, especially in the proof of concept stage of development where it is likely that you will be making a lot of changes to the prototypes. There is also a certain amount of middle ground between mild steel and titanium in the shape of high strength steels like chrome-moly alloys. It is certainly safe to say that there are a lot of difficulties associated in manufacturing in titanium.