Homogenisation behaviour of Nd2(Fe0.98Nb0.02)14B alloy

The effects of the homogenisation conditions on the microstructure of a Nd₂(Fe_0.98Nb_0.02)₁₄B alloy have been investigated. In the as cast condition the microstructure of the alloy contains four phases, the Nd₂Fe ₁₄B matrix phase, a Nb-containing ternary phase (Nb₂₆ Fe₃₂B₄₂), 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 Nb₂₆Fe₃₂ B₄₂ 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°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