Crystallization, morphology and magnetic properties of melt-spun (Nd,Pr,Dy)/sub 2/(Fe,Co,Mo)/sub 14/B//spl alpha/-Fe nanocomposites
Crystallization, phase evolution, nanostructure, exchange coupling, and hard magnetic properties of melt-spun Nd/sub 2.4/Pr/sub 5.6/Dy/sub 1/Fe/sub 85/B/sub 6/ and Nd/sub 2.4/Pr/sub 5.6/Dy/sub 1/Fe/sub 78/Co/sub 6/Mo/sub 1/B/sub 6/ nanocomposites have been studied. All the Nd/sub 2.4/Pr/sub 5.6/Dy/sub 1/Fe/sub 85/B/sub 6/ alloys annealed for 30 s at 565/spl deg/C or above contain nanostructured /spl alpha/-Fe and Nd/sub 2/Fe/sub 14/B-type (2:14:1) phases, whereas Nd/sub 2.4/Pr/sub 5.6/Dy/sub 1/Fe/sub 78/Co/sub 6/Mo/sub 1/B/sub 6/ alloys annealed at 600/spl deg/C or below are mainly composed of /spl alpha/-Fe and a metastable 1:7 phase. A small amount of 2:14:1 phase forms after annealing at 600/spl deg/C. When annealed at 640/spl deg/C or above, the hard phase in Nd/sub 2.4/Pr/sub 5.6/Dy/sub 1/Fe/sub 78/Co/sub 6/Mo/sub 1/B/sub 6/ alloys is the 2:14:1 phase rather than the 1:7 phase. The differences in magnetic properties of the Nd/sub 2.4/Pr/sub 5.6/Dy/sub 1/Fe/sub 85/B/sub 6/ and Nd/sub 2.4/Pr/sub 5.6/Dy/sub 1/Fe/sub 78/Co/sub 6/Mo/sub 1/B/sub 6/ nanocomposites at different anneal temperatures result from the different nanostructures, exchange coupling and phase components present in the alloys, in particular from the different amount of the 1:7 phase.
Nucleation and growth of γ-Fe precipitate in Cu-2%Fe alloy aged under high magnetic field
Abstract Cu-2wt%Fe alloy, an inexpensive candidate for a high strength conductor, depends for its conductivity on the precipitation of Fe. We applied an external 12 T high magnetic field (HMF) during ageing treatment of this alloy in order to study the resulting γ-Fe precipitation on the electrical conductivity. When the alloy was aged at 450 °C for up to 16 h, coherent γ-Fe precipitates formed within the Cu matrix. Between the γ-Fe precipitates and the Cu matrix, the lattice misfit was 1.4% ± 0.7% and the angle between closed packed planes was about 0.3°. These γ-Fe precipitates became semi-coherent with the surrounding Cu matrix in samples aged at 700 °C for over 0.5 h. HMF made insignificant contributions to both the morphology and the volume fraction of γ-Fe at 450 °C. At 700 °C, however, HMF promoted a transformation from coherent to semi-coherent γ-Fe precipitates. Applying HMF during ageing at 700 °C increased electrical conductivity. HMF had little influence on the nucleation of γ-Fe precipitation. We applied the Lifshitz-Slyozov-Wagner (LSW) formula to the coarsening data of the precipitates and determined that HMF increased the diffusion coefficient of Fe in Cu and promoted the growth of γ-Fe precipitation out of the Cu matrix.
Effect of roll speed on the magnetic properties of nanocomposite PrFeB magnets prepared by melt-spinning
Abstract Rapid solidified Pr x Fe 94− x B 6 alloys, with x ranging from 6 to 10 at%, were prepared by melt-spinning at several roll speeds to obtain nanocomposite PrFeB magnets with enhanced properties. Magnetic properties and grain-size measurements were performed on as-cast ribbons and were correlated to roll speed. It was found that the greatest J r enhancement occurred at roll speeds that led to grain sizes below ∼30 nm. Deviations from this optimum value, caused either by partial amorphisation or grain coarsening, greatly affected the values of J r , j H c and ( BH ) max .