2. Niobium Alloys
Niobium forms bcc structure over its entire temperature range.
Elements are added to Nb to improve:
1. creep rupture strength
2. resistance to high temperature oxidation
3. resistance to oxygen penetration
As no single alloy addition will accomplish all of these requirements – so multiple elements are often added

3. Ni-Alloy Compositions and Strengths
Niobium Alloys
Ni-Alloy Compositions and Strengths

4. Niobium Alloys Atomic diameters
Nb = Å Ta = Å - identical diameters!
Mo = Å W = Å Ti = Å
Zr = Å (strong hardening)
Ta is added to improve corrosion resistance – rather than strength
The addition of 1.0% Zr – or 10% Mo, W or Ti – increases the high temperature strength of Nb by a factor of two (2)
Dispersed phases of ZrO2 ThO2 ZrC and HfC – which strengthen by preventing recrystallization and grain boundary sliding – increase the high temperature strength of Nb by factors of 3-7 times

5. Preparation of Nb Alloys
Small quantities of pure Nb and Ta are prepared by electron beam melting under vacuum – while bulk quantities are prepared by powder metallurgy
In the later process – fine powders are pressed together to form a billet – which is densified (sintered) by heating (similar to ceramics)
This process is used to prepare alloys with dispersed oxides and carbides
The cast – or sintered – billets are cold formed at room temperature – by rolling, forging, drawing, etc – to form sheet, rod or wire

6. Preparation of Nb Alloys
Oxygen, nitrogen and hydrogen dissolve in Nb at temperatures above oC – so greatly reduce its room temperature ductility
These gases can be removed by heating in vacuum at oC

7. Preparation of Nb Alloys
Top: Nb sheet rolled 90% at room temperature – from 0.50 to 0.05 mm
Bottom: Same sheet after annealing for 1 h in vacuum at 1150 oC

8. The End Any questions or comments?