Structure and properties of gas-atomised nanocrystalline high-coercive FeNdB powders

Rare-earth-transition-metal permanent magnets are a major class of high-technology materials.. The demand of FeNdB permanent magnets is driven by the new or continuously-optimised applications, and this one requires the permanent improvements of their characteristics. Correlations between fabrication process of FeNdB materials with Co, Dy, Th, Ti, Mo additions and, microstructure, phase composition, magnetic and corrosion properties are revealed. The starting materials were prepared by the gas atomisation and powder-metallurgy processing. Magnetic measurements are performed on powders and sintered specimens.. As revealed, gas-atomised powders have amorphous or crystalline. structure depending on chemical composition and cooling rate. The corrosion resistance of gas-atomised,powders is two-times' higher in comparison with ordinary specimens. Coercivity of magnets fabricated from gas-atomised powders is 1.5 time larger than coercivity of sintered magnets. Gas-atomised: powders with a particle diameter. smaller than 30 mum exhibit very fine microstructure with amorphous component. For these fine-particle nanopowders, the coercivity up to 800 kA/m (10 kOe) is achieved. Thus the gas-atomisation method by sputtering, appears to be a promising technique for high coercivity powders' fabrication. Such powders are magnetically isotropic and are perspective materials for polymer-bounded and hot-pressed magnets' fabrication.