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

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

Niobium Alloys Atomic diameters Nb = 2.859 Å Ta = 2.859 Å - identical diameters! Mo = 2.745 Å W = 2.734 Å Ti = 2.894 Å Zr = 3.179 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

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

Preparation of Nb Alloys Oxygen, nitrogen and hydrogen dissolve in Nb at temperatures above 250-300 oC – so greatly reduce its room temperature ductility These gases can be removed by heating in vacuum at 1600-1700 oC

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

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