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Aniobium alloy is one in which the most common element is niobium.
The most common commercial niobium alloys are ferroniobium and nickel-niobium, produced by thermite reduction of appropriate mixtures of the oxides; these are not usable as engineering materials, but are used as convenient sources of niobium for specialist steels and nickel-based superalloys. Going via an iron-niobium or nickel-niobium alloy avoids problems associated with the high melting point of niobium.
Niobium-tin and Niobium-titanium are essential alloys for the industrial use of superconductors, since they remain superconducting in high magnetic fields (30T for Nb3Sn, 15T for NbTi); there are 1200 tons of NbTi in the magnets of the Large Hadron Collider, whilst Nb3Sn is used in the windings of almost all hospital MRI machines.
Niobium-titanium alloy, of the same composition as the superconducting one, is used for rivets in the aerospace industry; it is easier to form than CP titanium, and stronger at elevated (> 300 C) temperatures.
Niobium-1% zirconium is used in rocketry and in the nuclear industry; the space nuclear reactor presented in http://www.ornl.gov/~webworks/cppr/y2001/rpt/121399.pdf is predominantly made of this alloy. It is regarded as a low-strength alloy.
C-103, which is 89% Nb, 10% Hf and 1% Ti, was used for the rocket nozzle of the Apollo service module; it is regarded as a medium-strength alloy.
High-strength alloys include C-129Y (10% tungsten, 10% hafnium, 0.1% yttrium, balance niobium), Cb-752 (10% tungsten, 2.5% zirconium, and the even higher strength C-3009 (61% niobium, 30% tungsten, 9% hafnium); these can be used at temperatures up to 1650C with acceptable strength, though are expensive and hard to form.
Niobium alloys in general are inconvenient to weld: both sides of the weld need to be protected with a stream of pure inert gas, since hot niobium reacts with oxygen and nitrogen in the air. It is also necessary to take care (eg hard chrome-plating of all copper tooling) to avoid copper contamination.
http://www.wahchang.com/pages/products/data/niobium/Niobium.pdf
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