Homogenisation behaviour of Nd/sub 2/(Fe/sub 0.98/Nb/sub 0.02/)/sub 14/B alloy

The effects of the homogenisation conditions on the microstructure of a Nd/sub 2/(Fe/sub 0.98/Nb/sub 0.02/)/sub 14/B alloy have been investigated. In the as cast condition the microstructure of the alloy contains four phases, the Nd/sub 2/Fe/sub 14/B matrix phase, a Nb-containing ternary phase (Nb/sub 26/Fe/sub 32/B/sub 42/), Nd-rich regions and free iron. In contrast, the homogenised alloy contains only the first two phases and very small amounts of the Nd-rich phase. The Nb/sub 26/Fe/sub 32/B/sub 42/ ternary phase was found to originate (nucleate) in the heart of the free iron phase which provides strong evidence for the role of Nb in the removal of free iron from the microstructure. The electrical resistivity of the alloy was measured at regular intervals during the homogenisation process at 1000/spl deg/C and these studies revealed that, after 40 hours, the alloy was completely homogenised and this was in a good agreement with the microstructural studies. The resistance measurements also indicated a degree of anisotropy in the as-cast material and there was a maximum in resistance at an intermediate stage which could indicate an age hardening process. The resistance was found to correspond to a microhardness value.<
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