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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?

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  • $\begingroup$ You need to provide more detail and context to get decent answers. What, specifically, are you trying to achieve ? $\endgroup$ – Chris Johns Apr 20 '16 at 8:28
  • $\begingroup$ Technically, joining metal parts by using a different metal is called "brazing" or "soldering". "Welding" means melting and fusing the base metal directly. $\endgroup$ – Dave Tweed Apr 20 '16 at 10:53
  • $\begingroup$ At a glance at the phase diagrams, there are a lot of high-temperature intermetallic compounds with Ti-Cu and Ti-Ag. It isn't clear they would form welds with the same properties as the base material. As @ChrisJohns mentioned, it would be helpful to know what you are trying to achieve. Why do you want Cu and Ag? What is wrong with just using Ti as a base metal? As I understand some Ti alloys are weldable as is. $\endgroup$ – wwarriner Apr 20 '16 at 14:44
  • $\begingroup$ I wanted to attach muscle wire to it, in which case silver or copper would be conductive materials that would be able to attach to where the wire would be attached. That way the electricity would be able to complete a circuit from a power source (a microcontroller in this case), through one bundle of wire and back to the controller. $\endgroup$ – Tom Apr 21 '16 at 17:39
  • $\begingroup$ @Tom Do you need this to joint to be bio compatible? In general you should mill, drill, saw and cut Ti but not weld it or braze it. Ti can catch fire at (as far as I remember) temperatures as low as 400°C. This can occur if you use a worn off driller and much pressure for example. $\endgroup$ – MaestroGlanz Apr 23 '16 at 20:52
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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.

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  • $\begingroup$ You're right about being reactive to oxygen being a possible problem for me. Mechanical options aside, I suppose that steel, although heavier would be simpler to work with, because it doesn't react with air like titanium at high temperatures. Would silver still be an attractive option for brazing to steel? $\endgroup$ – Tom Apr 21 '16 at 18:40
  • $\begingroup$ What is it that you are trying to achieve ? $\endgroup$ – Chris Johns Apr 21 '16 at 18:50
  • $\begingroup$ I'm trying to attach nickel titanium wire to near a joint as artificial muscle. $\endgroup$ – Tom Apr 22 '16 at 2:50
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    $\begingroup$ Extra information: You can't extinguish Titanium with CO2, N2 or H2O. It will burn no matter what. A common extinguishing agent is sand. I'm not sure if SF6 is suitable for extinguishing. But could be. At least it is used for Mg. $\endgroup$ – MaestroGlanz Apr 23 '16 at 20:42

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